Temani Afif – CSS-Tricks https://css-tricks.com Tips, Tricks, and Techniques on using Cascading Style Sheets. Mon, 19 Jun 2023 23:15:06 +0000 en-US hourly 1 https://wordpress.org/?v=6.2.2 https://i0.wp.com/css-tricks.com/wp-content/uploads/2021/07/star.png?fit=32%2C32&ssl=1 Temani Afif – CSS-Tricks https://css-tricks.com 32 32 45537868 Different Ways to Get CSS Gradient Shadows https://css-tricks.com/different-ways-to-get-css-gradient-shadows/ https://css-tricks.com/different-ways-to-get-css-gradient-shadows/#respond Fri, 10 Feb 2023 15:13:42 +0000 https://css-tricks.com/?p=376764 It’s a question I hear asked quite often: Is it possible to create shadows from gradients instead of solid colors? There is no specific CSS property that does this (believe me, I’ve looked) and any blog post you find about …


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It’s a question I hear asked quite often: Is it possible to create shadows from gradients instead of solid colors? There is no specific CSS property that does this (believe me, I’ve looked) and any blog post you find about it is basically a lot of CSS tricks to approximate a gradient. We’ll actually cover some of those as we go.

But first… another article about gradient shadows? Really?

Yes, this is yet another post on the topic, but it is different. Together, we’re going to push the limits to get a solution that covers something I haven’t seen anywhere else: transparency. Most of the tricks work if the element has a non-transparent background but what if we have a transparent background? We will explore this case here!

Before we start, let me introduce my gradient shadows generator. All you have to do is to adjust the configuration, and get the code. But follow along because I’m going to help you understand all the logic behind the generated code.

Non-transparent solution

Let’s start with the solution that’ll work for 80% of most cases. The most typical case: you are using an element with a background, and you need to add a gradient shadow to it. No transparency issues to consider there.

The solution is to rely on a pseudo-element where the gradient is defined. You place it behind the actual element and apply a blur filter to it.

.box {
  position: relative;
}
.box::before {
  content: "";
  position: absolute;
  inset: -5px; /* control the spread */
  transform: translate(10px, 8px); /* control the offsets */
  z-index: -1; /* place the element behind */
  background: /* your gradient here */;
  filter: blur(10px); /* control the blur */
}

It looks like a lot of code, and that’s because it is. Here’s how we could have done it with a box-shadow instead if we were using a solid color instead of a gradient.

box-shadow: 10px 8px 10px 5px orange;

That should give you a good idea of what the values in the first snippet are doing. We have X and Y offsets, the blur radius, and the spread distance. Note that we need a negative value for the spread distance that comes from the inset property.

Here’s a demo showing the gradient shadow next to a classic box-shadow:

If you look closely you will notice that both shadows are a little different, especially the blur part. It’s not a surprise because I am pretty sure the filter property’s algorithm works differently than the one for box-shadow. That’s not a big deal since the result is, in the end, quite similar.

This solution is good, but still has a few drawbacks related to the z-index: -1 declaration. Yes, there is “stacking context” happening there!

I applied a transform to the main element, and boom! The shadow is no longer below the element. This is not a bug but the logical result of a stacking context. Don’t worry, I will not start a boring explanation about stacking context (I already did that in a Stack Overflow thread), but I’ll still show you how to work around it.

The first solution that I recommend is to use a 3D transform:

.box {
  position: relative;
  transform-style: preserve-3d;
}
.box::before {
  content: "";
  position: absolute;
  inset: -5px;
  transform: translate3d(10px, 8px, -1px); /* (X, Y, Z) */
  background: /* .. */;
  filter: blur(10px);
}

Instead of using z-index: -1, we will use a negative translation along the Z-axis. We will put everything inside translate3d(). Don’t forget to use transform-style: preserve-3d on the main element; otherwise, the 3D transform won’t take effect.

As far as I know, there is no side effect to this solution… but maybe you see one. If that’s the case, share it in the comment section, and let’s try to find a fix for it!

If for some reason you are unable to use a 3D transform, the other solution is to rely on two pseudo-elements — ::before and ::after. One creates the gradient shadow, and the other reproduces the main background (and other styles you might need). That way, we can easily control the stacking order of both pseudo-elements.

.box {
  position: relative;
  z-index: 0; /* We force a stacking context */
}
/* Creates the shadow */
.box::before {
  content: "";
  position: absolute;
  z-index: -2;
  inset: -5px;
  transform: translate(10px, 8px);
  background: /* .. */;
  filter: blur(10px);
}
/* Reproduces the main element styles */
.box::after {
  content: """;
  position: absolute;
  z-index: -1;
  inset: 0;
  /* Inherit all the decorations defined on the main element */
  background: inherit;
  border: inherit;
  box-shadow: inherit;
}

It’s important to note that we are forcing the main element to create a stacking context by declaring z-index: 0, or any other property that do the same, on it. Also, don’t forget that pseudo-elements consider the padding box of the main element as a reference. So, if the main element has a border, you need to take that into account when defining the pseudo-element styles. You will notice that I am using inset: -2px on ::after to account for the border defined on the main element.

As I said, this solution is probably good enough in a majority of cases where you want a gradient shadow, as long as you don’t need to support transparency. But we are here for the challenge and to push the limits, so even if you don’t need what is coming next, stay with me. You will probably learn new CSS tricks that you can use elsewhere.

Transparent solution

Let’s pick up where we left off on the 3D transform and remove the background from the main element. I will start with a shadow that has both offsets and spread distance equal to 0.

The idea is to find a way to cut or hide everything inside the area of the element (inside the green border) while keeping what is outside. We are going to use clip-path for that. But you might wonder how clip-path can make a cut inside an element.

Indeed, there’s no way to do that, but we can simulate it using a particular polygon pattern:

clip-path: polygon(-100vmax -100vmax,100vmax -100vmax,100vmax 100vmax,-100vmax 100vmax,-100vmax -100vmax,0 0,0 100%,100% 100%,100% 0,0 0)

Tada! We have a gradient shadow that supports transparency. All we did is add a clip-path to the previous code. Here is a figure to illustrate the polygon part.

Showing the clip-path coordinates for the element.

The blue area is the visible part after applying the clip-path. I am only using the blue color to illustrate the concept, but in reality, we will only see the shadow inside that area. As you can see, we have four points defined with a big value (B). My big value is 100vmax, but it can be any big value you want. The idea is to ensure we have enough space for the shadow. We also have four points that are the corners of the pseudo-element.

The arrows illustrate the path that defines the polygon. We start from (-B, -B) until we reach (0,0). In total, we need 10 points. Not eight points because two points are repeated twice in the path ((-B,-B) and (0,0)).

There’s still one more thing left for us to do, and it’s to account for the spread distance and the offsets. The only reason the demo above works is because it is a particular case where the offsets and spread distance are equal to 0.

Let’s define the spread and see what happens. Remember that we use inset with a negative value to do this:

The pseudo-element is now bigger than the main element, so the clip-path cuts more than we need it to. Remember, we always need to cut the part inside the main element (the area inside the green border of the example). We need to adjust the position of the four points inside of clip-path.

.box {
  --s: 10px; /* the spread  */
  position: relative;
}
.box::before {
  inset: calc(-1 * var(--s));
  clip-path: polygon(
    -100vmax -100vmax,
     100vmax -100vmax,
     100vmax 100vmax,
    -100vmax 100vmax,
    -100vmax -100vmax,
    calc(0px  + var(--s)) calc(0px  + var(--s)),
    calc(0px  + var(--s)) calc(100% - var(--s)),
    calc(100% - var(--s)) calc(100% - var(--s)),
    calc(100% - var(--s)) calc(0px  + var(--s)),
    calc(0px  + var(--s)) calc(0px  + var(--s))
  );
}

We’ve defined a CSS variable, --s, for the spread distance and updated the polygon points. I didn’t touch the points where I am using the big value. I only update the points that define the corners of the pseudo-element. I increase all the zero values by --s and decrease the 100% values by --s.

It’s the same logic with the offsets. When we translate the pseudo-element, the shadow is out of alignment, and we need to rectify the polygon again and move the points in the opposite direction.

.box {
  --s: 10px; /* the spread */
  --x: 10px; /* X offset */
  --y: 8px;  /* Y offset */
  position: relative;
}
.box::before {
  inset: calc(-1 * var(--s));
  transform: translate3d(var(--x), var(--y), -1px);
  clip-path: polygon(
    -100vmax -100vmax,
     100vmax -100vmax,
     100vmax 100vmax,
    -100vmax 100vmax,
    -100vmax -100vmax,
    calc(0px  + var(--s) - var(--x)) calc(0px  + var(--s) - var(--y)),
    calc(0px  + var(--s) - var(--x)) calc(100% - var(--s) - var(--y)),
    calc(100% - var(--s) - var(--x)) calc(100% - var(--s) - var(--y)),
    calc(100% - var(--s) - var(--x)) calc(0px  + var(--s) - var(--y)),
    calc(0px  + var(--s) - var(--x)) calc(0px  + var(--s) - var(--y))
  );
}

There are two more variables for the offsets: --x and --y. We use them inside of transform and we also update the clip-path values. We still don’t touch the polygon points with big values, but we offset all the others — we reduce --x from the X coordinates, and --y from the Y coordinates.

Now all we have to do is to update a few variables to control the gradient shadow. And while we are at it, let’s also make the blur radius a variable as well:

Do we still need the 3D transform trick?

It all depends on the border. Don’t forget that the reference for a pseudo-element is the padding box, so if you apply a border to your main element, you will have an overlap. You either keep the 3D transform trick or update the inset value to account for the border.

Here is the previous demo with an updated inset value in place of the 3D transform:

I‘d say this is a more suitable way to go because the spread distance will be more accurate, as it starts from the border-box instead of the padding-box. But you will need to adjust the inset value according to the main element’s border. Sometimes, the border of the element is unknown and you have to use the previous solution.

With the earlier non-transparent solution, it’s possible you will face a stacking context issue. And with the transparent solution, it’s possible you face a border issue instead. Now you have options and ways to work around those issues. The 3D transform trick is my favorite solution because it fixes all the issues (The online generator will consider it as well)

Adding a border radius

If you try adding border-radius to the element when using the non-transparent solution we started with, it is a fairly trivial task. All you need to do is to inherit the same value from the main element, and you are done.

Even if you don’t have a border radius, it’s a good idea to define border-radius: inherit. That accounts for any potential border-radius you might want to add later or a border radius that comes from somewhere else.

It’s a different story when dealing with the transparent solution. Unfortunately, it means finding another solution because clip-path cannot deal with curvatures. That means we won’t be able to cut the area inside the main element.

We will introduce the mask property to the mix.

This part was very tedious, and I struggled to find a general solution that doesn’t rely on magic numbers. I ended up with a very complex solution that uses only one pseudo-element, but the code was a lump of spaghetti that covers only a few particular cases. I don’t think it is worth exploring that route.

I decided to insert an extra element for the sake of simpler code. Here’s the markup:

<div class="box">
  <sh></sh>
</div>

I am using a custom element, <sh>, to avoid any potential conflict with external CSS. I could have used a <div>, but since it’s a common element, it can easily be targeted by another CSS rule coming from somewhere else that can break our code.

The first step is to position the <sh> element and purposely create an overflow:

.box {
  --r: 50px;
  position: relative;
  border-radius: var(--r);
}
.box sh {
  position: absolute;
  inset: -150px;
  border: 150px solid #0000;
  border-radius: calc(150px + var(--r));
}

The code may look a bit strange, but we’ll get to the logic behind it as we go. Next, we create the gradient shadow using a pseudo-element of <sh>.

.box {
  --r: 50px;
  position: relative;
  border-radius: var(--r);
  transform-style: preserve-3d;
}
.box sh {
  position: absolute;
  inset: -150px;
  border: 150px solid #0000;
  border-radius: calc(150px + var(--r));
  transform: translateZ(-1px)
}
.box sh::before {
  content: "";
  position: absolute;
  inset: -5px;
  border-radius: var(--r);
  background: /* Your gradient */;
  filter: blur(10px);
  transform: translate(10px,8px);
}

As you can see, the pseudo-element uses the same code as all the previous examples. The only difference is the 3D transform defined on the <sh> element instead of the pseudo-element. For the moment, we have a gradient shadow without the transparency feature:

Note that the area of the <sh> element is defined with the black outline. Why I am doing this? Because that way, I am able to apply a mask on it to hide the part inside the green area and keep the overflowing part where we need to see the shadow.

I know it’s a bit tricky, but unlike clip-path, the mask property doesn’t account for the area outside an element to show and hide things. That’s why I was obligated to introduce the extra element — to simulate the “outside” area.

Also, note that I am using a combination of border and inset to define that area. This allows me to keep the padding-box of that extra element the same as the main element so that the pseudo-element won’t need additional calculations.

Another useful thing we get from using an extra element is that the element is fixed, and only the pseudo-element is moving (using translate). This will allow me to easily define the mask, which is the last step of this trick.

mask:
  linear-gradient(#000 0 0) content-box,
  linear-gradient(#000 0 0);
mask-composite: exclude;

It’s done! We have our gradient shadow, and it supports border-radius! You probably expected a complex mask value with oodles of gradients, but no! We only need two simple gradients and a mask-composite to complete the magic.

Let’s isolate the <sh> element to understand what is happening there:

.box sh {
  position: absolute;
  inset: -150px;
  border: 150px solid red;
  background: lightblue;
  border-radius: calc(150px + var(--r));
}

Here’s what we get:

Note how the inner radius matches the main element’s border-radius. I have defined a big border (150px) and a border-radius equal to the big border plus the main element’s radius. On the outside, I have a radius equal to 150px + R. On the inside, I have 150px + R - 150px = R.

We must hide the inner (blue) part and make sure the border (red) part is still visible. To do that, I’ve defined two mask layers —One that covers only the content-box area and another that covers the border-box area (the default value). Then I excluded one from another to reveal the border.

mask:
  linear-gradient(#000 0 0) content-box,
  linear-gradient(#000 0 0);
mask-composite: exclude;

I used the same technique to create a border that supports gradients and border-radius. Ana Tudor has also a good article about masking composite that I invite you to read.

Are there any drawbacks to this method?

Yes, this definitely not perfect. The first issue you may face is related to using a border on the main element. This may create a small misalignment in the radii if you don’t account for it. We have this issue in our example, but perhaps you can hardly notice it.

The fix is relatively easy: Add the border’s width for the <sh> element’s inset.

.box {
  --r: 50px;
  border-radius: var(--r);
  border: 2px solid;
}
.box sh {
  position: absolute;
  inset: -152px; /* 150px + 2px */
  border: 150px solid #0000;
  border-radius: calc(150px + var(--r));
}

Another drawback is the big value we’re using for the border (150px in the example). This value should be big enough to contain the shadow but not too big to avoid overflow and scrollbar issues. Luckily, the online generator will calculate the optimal value considering all the parameters.

The last drawback I am aware of is when you’re working with a complex border-radius. For example, if you want a different radius applied to each corner, you must define a variable for each side. It’s not really a drawback, I suppose, but it can make your code a bit tougher to maintain.

.box {
  --r-top: 10px;
  --r-right: 40px;
  --r-bottom: 30px;
  --r-left: 20px;
  border-radius: var(--r-top) var(--r-right) var(--r-bottom) var(--r-left);
}
.box sh {
  border-radius: calc(150px + var(--r-top)) calc(150px + var(--r-right)) calc(150px + var(--r-bottom)) calc(150px + var(--r-left));
}
.box sh:before {
  border-radius: var(--r-top) var(--r-right) var(--r-bottom) var(--r-left);
}

The online generator only considers a uniform radius for the sake of simplicity, but you now know how to modify the code if you want to consider a complex radius configuration.

Wrapping up

We’ve reached the end! The magic behind gradient shadows is no longer a mystery. I tried to cover all the possibilities and any possible issues you might face. If I missed something or you discover any issue, please feel free to report it in the comment section, and I’ll check it out.

Again, a lot of this is likely overkill considering that the de facto solution will cover most of your use cases. Nevertheless, it’s good to know the “why” and “how” behind the trick, and how to overcome its limitations. Plus, we got good exercise playing with CSS clipping and masking.

And, of course, you have the online generator you can reach for anytime you want to avoid the hassle.


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A Fancy Hover Effect For Your Avatar https://css-tricks.com/a-fancy-hover-effect-for-your-avatar/ https://css-tricks.com/a-fancy-hover-effect-for-your-avatar/#comments Fri, 03 Feb 2023 15:11:46 +0000 https://css-tricks.com/?p=376676 Do you know that kind of effect where someone’s head is poking through a circle or hole? The famous Porky Pig animation where he waves goodbye while popping out of a series of red rings is the perfect example, and …


A Fancy Hover Effect For Your Avatar originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

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Do you know that kind of effect where someone’s head is poking through a circle or hole? The famous Porky Pig animation where he waves goodbye while popping out of a series of red rings is the perfect example, and Kilian Valkhof actually re-created that here on CSS-Tricks a while back.

I have a similar idea but tackled a different way and with a sprinkle of animation. I think it’s pretty practical and makes for a neat hover effect you can use on something like your own avatar.

See that? We’re going to make a scaling animation where the avatar seems to pop right out of the circle it’s in. Cool, right? Don’t look at the code and let’s build this animation together step-by-step.

The HTML: Just one element

If you haven’t checked the code of the demo and you are wondering how many divs this’ll take, then stop right there, because our markup is nothing but a single image element:

<img src="" alt="">

Yes, a single element! The challenging part of this exercise is using the smallest amount of code possible. If you have been following me for a while, you should be used to this. I try hard to find CSS solutions that can be achieved with the smallest, most maintainable code possible.

I wrote a series of articles here on CSS-Tricks where I explore different hover effects using the same HTML markup containing a single element. I go into detail on gradients, masking, clipping, outlines, and even layout techniques. I highly recommend checking those out because I will re-use many of the tricks in this post.

An image file that’s square with a transparent background will work best for what we’re doing. Here’s the one I’m using if you want start with that.

Designed by Cang

I’m hoping to see lots of examples of this as possible using real images — so please share your final result in the comments when you’re done so we can build a collection!

Before jumping into CSS, let’s first dissect the effect. The image gets bigger on hover, so we’ll for sure use transform: scale() in there. There’s a circle behind the avatar, and a radial gradient should do the trick. Finally, we need a way to create a border at the bottom of the circle that creates the appearance of the avatar behind the circle.

Let’s get to work!

The scale effect

Let’s start by adding the transform:

img {
  width: 280px;
  aspect-ratio: 1;
  cursor: pointer;
  transition: .5s;
}
img:hover {
  transform: scale(1.35);
}

Nothing complicated yet, right? Let’s move on.

The circle

We said that the background would be a radial gradient. That’s perfect because we can create hard stops between the colors of a radial gradient, which make it look like we’re drawing a circle with solid lines.

img {
  --b: 5px; /* border width */

  width: 280px;
  aspect-ratio: 1;
  background:
    radial-gradient(
      circle closest-side,
      #ECD078 calc(99% - var(--b)),
      #C02942 calc(100% - var(--b)) 99%,
      #0000
    );
  cursor: pointer;
  transition: .5s;
}
img:hover {
  transform: scale(1.35);
}

Note the CSS variable, --b, I’m using there. It represents the thickness of the “border” which is really just being used to define the hard color stops for the red part of the radial gradient.

The next step is to play with the gradient size on hover. The circle needs to keep its size as the image grows. Since we are applying a scale() transformation, we actually need to decrease the size of the circle because it otherwise scales up with the avatar. So, while the image scales up, we need the gradient to scale down.

Let’s start by defining a CSS variable, --f, that defines the “scale factor”, and use it to set the size of the circle. I’m using 1 as the default value, as in that’s the initial scale for the image and the circle that we transform from.

Here is a demo to illustrate the trick. Hover to see what is happening behind the scenes:

I added a third color to the radial-gradient to better identify the area of the gradient on hover:

radial-gradient(
  circle closest-side,
  #ECD078 calc(99% - var(--b)),
  #C02942 calc(100% - var(--b)) 99%,
  lightblue
);

Now we have to position our background at the center of the circle and make sure it takes up the full height. I like to declare everything directly on the background shorthand property, so we can add our background positioning and make sure it doesn’t repeat by tacking on those values right after the radial-gradient():

background: radial-gradient() 50% / calc(100% / var(--f)) 100% no-repeat;

The background is placed at the center (50%), has a width equal to calc(100%/var(--f)), and has a height equal to 100%.

Nothing scales when --f is equal to 1 — again, our initial scale. Meanwhile, the gradient takes up the full width of the container. When we increase --f, the element’s size grows — thanks to the scale() transform — and the gradient’s size decreases.

Here’s what we get when we apply all of this to our demo:

We’re getting closer! We have the overflow effect at the top, but we still need to hide the bottom part of the image, so it looks like it is popping out of the circle rather than sitting in front of it. That’s the tricky part of this whole thing and is what we’re going to do next.

The bottom border

I first tried tackling this with the border-bottom property, but I was unable to find a way to match the size of the border to the size to the circle. Here’s the best I could get and you can immediately see it’s wrong:

The actual solution is to use the outline property. Yes, outline, not border. In a previous article, I show how outline is powerful and allows us to create cool hover effects. Combined with outline-offset, we have exactly what we need for our effect.

The idea is to set an outline on the image and adjust its offset to create the bottom border. The offset will depend on the scaling factor the same way the gradient size did.

Now we have our bottom “border” (actually an outline) combined with the “border” created by the gradient to create a full circle. We still need to hide portions of the outline (from the top and the sides), which we’ll get to in a moment.

Here’s our code so far, including a couple more CSS variables you can use to configure the image size (--s) and the “border” color (--c):

img {
  --s: 280px; /* image size */
  --b: 5px; /* border thickness */
  --c: #C02942; /* border color */
  --f: 1; /* initial scale */

  width: var(--s);
  aspect-ratio: 1;
  cursor: pointer;
  border-radius: 0 0 999px 999px;
  outline: var(--b) solid var(--c);
  outline-offset: calc((1 / var(--f) - 1) * var(--s) / 2 - var(--b));
  background: 
    radial-gradient(
      circle closest-side,
      #ECD078 calc(99% - var(--b)),
      var(--c) calc(100% - var(--b)) 99%,
      #0000
    ) 50% / calc(100% / var(--f)) 100% no-repeat;
  transform: scale(var(--f));
  transition: .5s;
}
img:hover {
  --f: 1.35; /* hover scale */
}

Since we need a circular bottom border, we added a border-radius on the bottom side, allowing the outline to match the curvature of the gradient.

The calculation used on outline-offset is a lot more straightforward than it looks. By default, outline is drawn outside of the element’s box. And in our case, we need it to overlap the element. More precisely, we need it to follow the circle created by the gradient.

Diagram of the background transition.

When we scale the element, we see the space between the circle and the edge. Let’s not forget that the idea is to keep the circle at the same size after the scale transformation runs, which leaves us with the space we will use to define the outline’s offset as illustrated in the above figure.

Let’s not forget that the second element is scaled, so our result is also scaled… which means we need to divide the result by f to get the real offset value:

Offset = ((f - 1) * S/2) / f = (1 - 1/f) * S/2

We add a negative sign since we need the outline to go from the outside to the inside:

Offset = (1/f - 1) * S/2

Here’s a quick demo that shows how the outline follows the gradient:

You may already see it, but we still need the bottom outline to overlap the circle rather than letting it bleed through it. We can do that by removing the border’s size from the offset:

outline-offset: calc((1 / var(--f) - 1) * var(--s) / 2) - var(--b));

Now we need to find how to remove the top part from the outline. In other words, we only want the bottom part of the image’s outline.

First, let’s add space at the top with padding to help avoid the overlap at the top:

img {
  --s: 280px; /* image size */
  --b: 5px;   /* border thickness */
  --c: #C02942; /* border color */
  --f: 1; /* initial scale */

  width: var(--s);
  aspect-ratio: 1;
  padding-block-start: calc(var(--s)/5);
  /* etc. */
}
img:hover {
  --f: 1.35; /* hover scale */
}

There is no particular logic to that top padding. The idea is to ensure the outline doesn’t touch the avatar’s head. I used the element’s size to define that space to always have the same proportion.

Note that I have added the content-box value to the background:

background:
  radial-gradient(
    circle closest-side,
    #ECD078 calc(99% - var(--b)),
    var(--c) calc(100% - var(--b)) 99%,
    #0000
  ) 50%/calc(100%/var(--f)) 100% no-repeat content-box;

We need this because we added padding and we only want the background set to the content box, so we must explicitly tell the background to stop there.

Adding CSS mask to the mix

We reached the last part! All we need to do is to hide some pieces, and we are done. For this, we will rely on the mask property and, of course, gradients.

Here is a figure to illustrate what we need to hide or what we need to show to be more accurate

Showing how the mask applies to the bottom portion of the circle.

The left image is what we currently have, and the right is what we want. The green part illustrates the mask we must apply to the original image to get the final result.

We can identify two parts of our mask:

  • A circular part at the bottom that has the same dimension and curvature as the radial gradient we used to create the circle behind the avatar
  • A rectangle at the top that covers the area inside the outline. Notice how the outline is outside the green area at the top — that’s the most important part, as it allows the outline to be cut so that only the bottom part is visible.

Here’s our final CSS:

img {
  --s: 280px; /* image size */
  --b: 5px; /* border thickness */
  --c: #C02942; /* border color */
  --f: 1; /* initial scale */

  --_g: 50% / calc(100% / var(--f)) 100% no-repeat content-box;
  --_o: calc((1 / var(--f) - 1) * var(--s) / 2 - var(--b));

  width: var(--s);
  aspect-ratio: 1;
  padding-top: calc(var(--s)/5);
  cursor: pointer;
  border-radius: 0 0 999px 999px;
  outline: var(--b) solid var(--c);
  outline-offset: var(--_o);
  background: 
    radial-gradient(
      circle closest-side,
      #ECD078 calc(99% - var(--b)),
      var(--c) calc(100% - var(--b)) 99%,
      #0000) var(--_g);
  mask:
    linear-gradient(#000 0 0) no-repeat
    50% calc(-1 * var(--_o)) / calc(100% / var(--f) - 2 * var(--b)) 50%,
    radial-gradient(
      circle closest-side,
      #000 99%,
      #0000) var(--_g);
  transform: scale(var(--f));
  transition: .5s;
}
img:hover {
  --f: 1.35; /* hover scale */
}

Let’s break down that mask property. For starters, notice that a similar radial-gradient() from the background property is in there. I created a new variable, --_g, for the common parts to make things less cluttered.

--_g: 50% / calc(100% / var(--f)) 100% no-repeat content-box;

mask:
  radial-gradient(
    circle closest-side,
    #000 99%,
    #0000) var(--_g);

Next, there’s a linear-gradient() in there as well:

--_g: 50% / calc(100% / var(--f)) 100% no-repeat content-box;

mask:
  linear-gradient(#000 0 0) no-repeat
    50% calc(-1 * var(--_o)) / calc(100% / var(--f) - 2 * var(--b)) 50%,
  radial-gradient(
    circle closest-side,
    #000 99%,
    #0000) var(--_g);

This creates the rectangle part of the mask. Its width is equal to the radial gradient’s width minus twice the border thickness:

calc(100% / var(--f) - 2 * var(--b))

The rectangle’s height is equal to half, 50%, of the element’s size.

We also need the linear gradient placed at the horizontal center (50%) and offset from the top by the same value as the outline’s offset. I created another CSS variable, --_o, for the offset we previously defined:

--_o: calc((1 / var(--f) - 1) * var(--s) / 2 - var(--b));

One of the confusing things here is that we need a negative offset for the outline (to move it from outside to inside) but a positive offset for the gradient (to move from top to bottom). So, if you’re wondering why we multiply the offset, --_o, by -1, well, now you know!

Here is a demo to illustrate the mask’s gradient configuration:

Hover the above and see how everything move together. The middle box illustrates the mask layer composed of two gradients. Imagine it as the visible part of the left image, and you get the final result on the right!

Wrapping up

Oof, we’re done! And not only did we wind up with a slick hover animation, but we did it all with a single HTML <img> element. Just that and less than 20 lines of CSS trickery!

Sure, we relied on some little tricks and math formulas to reach such a complex effect. But we knew exactly what to do since we identified the pieces we needed up-front.

Could we have simplified the CSS if we allowed ourselves more HTML? Absolutely. But we’re here to learn new CSS tricks! This was a good exercise to explore CSS gradients, masking, the outline property’s behavior, transformations, and a whole bunch more. If you felt lost at any point, then definitely check out my series that uses the same general concepts. It sometimes helps to see more examples and use cases to drive a point home.

I will leave you with one last demo that uses photos of popular CSS developers. Don’t forget to show me a demo with your own image so I can add it to the collection!


A Fancy Hover Effect For Your Avatar originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

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CSS Infinite 3D Sliders https://css-tricks.com/css-infinite-3d-sliders/ https://css-tricks.com/css-infinite-3d-sliders/#comments Fri, 16 Dec 2022 14:58:08 +0000 https://css-tricks.com/?p=375621 In this series, we’ve been making image sliders with nothing but HTML and CSS. The idea is that we can use the same markup but different CSS to get wildly different results, no matter how many images we toss …


CSS Infinite 3D Sliders originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>
In this series, we’ve been making image sliders with nothing but HTML and CSS. The idea is that we can use the same markup but different CSS to get wildly different results, no matter how many images we toss in. We started with a circular slider that rotates infinitely, sort of like a fidget spinner that holds images. Then we made one that flips through a stack of photos.

This time around, we’re diving into the third dimension. It’s going to look tough at first, but lots of the code we’re looking at is exactly what we used in the first two articles in this series, with some modifications. So, if you’re just now getting into the series, I’d suggest checking out the others for context on the concepts we’re using here.

CSS Sliders series

This is what we’re aiming for:

At first glance, it looks like we have a rotating cube with four images. But in reality, we’re dealing with six images in total. Here is the slider from a different angle:

Now that we have a good visual for how the images are arranged, let’s dissect the code to see how we get there.

The basic setup

Same HTML as the rest of the sliders we’ve used for the other sliders:

<div class="gallery">
  <img src="" alt="">
  <img src="" alt="">
  <img src="" alt="">
  <img src="" alt="">
  <img src="" alt="">
</div>

And once again, we’re using CSS Grid to place the images in a stack, one on top of another:

.gallery {
  display: grid;
}
.gallery > img {
  grid-area: 1 / 1;
  width: 160px;
  aspect-ratio: 1;
  object-fit: cover;
}

The animation

The logic for this slider is very similar to the circular slider from the first article. In fact, if you check the video above again, you can see that the images are placed in a way that creates a polygon. After a full rotation, it returns to the first image.

We relied on the CSS transform-origin and animation-delay properties for that first slider. The same animation is applied to all of the image elements, which rotate around the same point. Then, by using different delays, we correctly place all the images around a big circle.

The implementation will be a bit different for our 3D slider. Using transform-origin won’t work here because we’re working in 3D, so we will use transform instead to correctly place all the images, then rotate the container.

We’re reaching for Sass again so we can loop through the number of images and apply our transforms:

@for $i from 1 to ($n + 1) {
  .gallery > img:nth-child(#{$i}) {
     transform: 
       rotate(#{360*($i - 1) / $n}deg) /* 1 */
       translateY(50% / math.tan(180deg / $n)) /* 2 */ 
       rotateX(90deg); /* 3 */
  }
}

You might be wondering why we’re jumping straight into Sass. We started with a fixed number of images using vanilla CSS in the other articles before generalizing the code with Sass to account for any number (N) of images. Well, I think you get the idea now and we can cut out all that discovery work to get to the real implementation.

The transform property is taking three values, which I’ve illustrated here:

Showing the three phases of the image slider layout.

We first rotate all the images above each other. The angle of rotation depends on the number of images. For N images, we have an increment equal to 360deg/N. Then we translate all of the images by the same amount in a way that makes their center points meet on the sides.

Showing the stack of images arranged flat in a circle with a red line running through the center point of the images.

There’s some boring geometry that helps explain how all this works, but the distance is equal to 50%/tan(180deg/N). We dealt with a similar equation when making the circular slider ( transform-origin: 50% 50%/sin(180deg/N) ).

Finally, we rotate the images around the x-axis by 90deg to get the arrangement we want. Here is a video that illustrates what the last rotation is doing:

Now all we have to do is to rotate the whole container to create our infinite slider.

.gallery {
  transform-style: preserve-3d;
  --_t: perspective(280px) rotateX(-90deg);
  animation: r 12s cubic-bezier(.5, -0.2, .5, 1.2) infinite;
}
@keyframes r {
  0%, 3% {transform: var(--_t) rotate(0deg); }
  @for $i from 1 to $n {
    #{($i/$n)*100 - 2}%, 
    #{($i/$n)*100 + 3}% {
      transform: var(--_t) rotate(#{($i / $n) * -360}deg);
    }  
  }
  98%, 100% { transform: var(--_t) rotate(-360deg); }
}

That code might be hard to understand, so let’s actually step back a moment and revisit the animation we made for the circular slider. This is what we wrote in that first article:

.gallery {
  animation: m 12s cubic-bezier(.5, -0.2, .5, 1.2) infinite;
}
@keyframes m {
  0%, 3% { transform: rotate(0); }
  @for $i from 1 to $n {
    #{($i / $n) * 100 - 2}%,
    #{($i / $n) * 100 + 3}% { 
      transform: rotate(#{($i / $n) * -360}deg);
    }  
  }
  98%, 100% { transform: rotate(-360deg); }
}

The keyframes are almost identical. We have the same percentage values, the same loop, and the same rotation.

Why are both the same? Because their logic is the same. In both cases, the images are arranged around a circular shape and we need to rotate the whole thing to show each image. That’s how I was able to copy the keyframes from the circular slider and use that same code for our 3D slider. The only difference is that we need to rotate the container by -90deg along the x-axis to see the images since we have already rotated them by 90deg on the same axis. Then we add a touch of perspective to get the 3D effect.

That’s it! Our slider is done. Here is the full demo again. All you have to do is to add as many images as you want and update one variable to get it going.

Vertical 3D slider

Since we are playing in the 3D space, why not make a vertical version of the previous slider? The last one rotates along the z-axis, but we can also move along the x-axis if we want.

If you compare the code for both versions of this slider, you might not immediately spot the difference because it’s only one character! I replaced rotate() with rotateX() inside the keyframes and the image transform. That’s it!

It should be noted that rotate() is equivalent to rotateZ(), so by changing the axis from Z to X we transform the slider from the horizontal version into the vertical one.

Cube slider

We cannot talk about 3D in CSS without talking about cubes. And yes, that means we are going to make another version of the slider.

The idea behind this version of the slider is to create an actual cube shape with the images and rotate the full thing in around the different axis. Since it’s a cube, we’re dealing with six faces. We’ll use six images, one for each face of the cube. So, no Sass but back to vanilla CSS.

That animation is a little overwhelming, right? Where do you even start?

We have six faces, so we need to perform at least six rotations so that each image gets a turn. Well, actually, we need five rotations — the last one brings us back to the first image face. If you go grab a Rubik’s Cube — or some other cube-shaped object like dice — and rotate it with your hand, you’ll have a good idea of what we’re doing.

.gallery {
  --s: 250px; /* the size */

  transform-style: preserve-3d;
  --_p: perspective(calc(2.5*var(--s)));
  animation: r 9s infinite cubic-bezier(.5, -0.5, .5, 1.5);
}

@keyframes r {
  0%, 3%   { transform: var(--_p); }
  14%, 19% { transform: var(--_p) rotateX(90deg); }
  31%, 36% { transform: var(--_p) rotateX(90deg) rotateZ(90deg); }
  47%, 52% { transform: var(--_p) rotateX(90deg) rotateZ(90deg) rotateY(-90deg); }
  64%, 69% { transform: var(--_p) rotateX(90deg) rotateZ(90deg) rotateY(-90deg) rotateX(90deg); }
  81%, 86% { transform: var(--_p) rotateX(90deg) rotateZ(90deg) rotateY(-90deg) rotateX(90deg) rotateZ(90deg); }
  97%, 100%{ transform: var(--_p) rotateX(90deg) rotateZ(90deg) rotateY(-90deg) rotateX(90deg) rotateZ(90deg) rotateY(-90deg); }
}

The transform property starts with zero rotations and, on each state, we append a new rotation on a specific axis until we reach six rotations. Then we are back to the first image.

Let’s not forget the placement of our images. Each one is applied to a face of the cube using transform:

.gallery img {
  grid-area: 1 / 1;
  width: var(--s);
  aspect-ratio: 1;
  object-fit: cover;
  transform: var(--_t,) translateZ(calc(var(--s) / 2));
}
.gallery img:nth-child(2) { --_t: rotateX(-90deg); }
.gallery img:nth-child(3) { --_t: rotateY( 90deg) rotate(-90deg); }
.gallery img:nth-child(4) { --_t: rotateX(180deg) rotate( 90deg); }
.gallery img:nth-child(5) { --_t: rotateX( 90deg) rotate( 90deg); }
.gallery img:nth-child(6) { --_t: rotateY(-90deg); }

You are probably thinking there is weird complex logic behind the values I’m using there, right? Well, no. All I did was open DevTools and play with different rotation values for each image until I got it right. It may sound stupid but, hey, it works — especially since we have a fixed number of images and we are not looking for something that supports N images.

In fact, forget the values I’m using and try to do the placement on your own as an exercise. Start with all the images stacked on top of each other, open the DevTools, and go! You will probably end up with different code and that’s totally fine. There can be different ways to position the images.

What’s the trick with the comma inside the var()? Is it a typo?

It’s not a typo so don’t remove it! If you do remove it, you will notice that it affects the placement of the first image. You can see that in my code I defined --_t for all the images except the first one because I only need a translation for it. That comma makes the variable fall back to a null value. Without the comma, we won’t have a fallback and the whole value will be invalid.

From the specification:

Note: That is, var(--a,) is a valid function, specifying that if the --a custom property is invalid or missing, the var()` should be replaced with nothing.

Random cube slider

A little bit of randomness can be a nice enhancement for this sort of animation. So, rather than rotate the cube in sequential order, we can roll the dice so to speak, and let the cube roll however it will.

Cool right? I don’t know about you, but I like this version better! It’s more interesting and the transitions are satisfying to watch. And guess what? You can play with the values to create your own random cube slider!

The logic is actual not random at all — it just appears that way. You define a transform on each keyframe that allows you to show one face and… well, that’s really it! You can pick any order you want.

@keyframes r {
  0%, 3%   { transform: var(--_p) rotate3d( 0, 0, 0,  0deg); }
  14%,19%  { transform: var(--_p) rotate3d(-1, 1, 0,180deg); }
  31%,36%  { transform: var(--_p) rotate3d( 0,-1, 0, 90deg); }
  47%,52%  { transform: var(--_p) rotate3d( 1, 0, 0, 90deg); }
  64%,69%  { transform: var(--_p) rotate3d( 1, 0, 0,-90deg); }
  81%,86%  { transform: var(--_p) rotate3d( 0, 1, 0, 90deg); }
  97%,100% { transform: var(--_p) rotate3d( 0, 0, 0,  0deg); }
}

I am using rotate3d() this time but am still relying on DevTools to find the values that feel “right” to me. Don’t try to find a relationship between the keyframes because there simply isn’t one. I’m defining separate transforms and then watching the “random” result. Make sure the first image is the first and last frames, respectively, and show a different image on each of the other frames.

You are not obligated to use a rotate3d() transform as I did. You can also chain different rotations like we did in the previous example. Play around and see what you can come up with! I will be waiting for you to share your version with me in the comments section!

Wrapping up

I hope you enjoyed this little series. We built some fun (and funny) sliders while learning a lot about all kinds of CSS concepts along the way — from grid placement and stacking order, to animation delays and transforms. We even got to play with a dash of Sass to loop through an array of elements.

And we did it all with the exact same HTML for each and every slider we made. How cool is that? CSS is dang powerful and capable of accomplishing so much without the aid of JavaScript.


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CSS Infinite Slider Flipping Through Polaroid Images https://css-tricks.com/css-infinite-slider-flipping-through-polaroid-images/ https://css-tricks.com/css-infinite-slider-flipping-through-polaroid-images/#comments Fri, 09 Dec 2022 14:26:39 +0000 https://css-tricks.com/?p=375537 In the last article, we made a pretty cool little slider (or “carousel” if that’s what you prefer) that rotates in a circular direction. This time we are going to make one that flips through a stack of Polaroid …


CSS Infinite Slider Flipping Through Polaroid Images originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>
In the last article, we made a pretty cool little slider (or “carousel” if that’s what you prefer) that rotates in a circular direction. This time we are going to make one that flips through a stack of Polaroid images.

Cool right? Don’t look at the code quite yet because there’s a lot to unravel. Join me, will ya?

CSS Sliders series

The basic setup

Most of the HTML and CSS for this slider is similar to the circular one we made last time. In fact, we’re using the exact same markup:

<div class="gallery">
  <img src="" alt="">
  <img src="" alt="">
  <img src="" alt="">
  <img src="" alt="">
</div>

And this is the basic CSS that sets our parent .gallery container as a grid where all the images are stacked one on top of one another:

.gallery  {
  display: grid;
  width: 220px; /* controls the size */
}
.gallery > img {
  grid-area: 1 / 1;
  width: 100%;
  aspect-ratio: 1;
  object-fit: cover;
  border: 10px solid #f2f2f2;
  box-shadow: 0 0 4px #0007;
}

Nothing complex so far. Even for the Polaroid-like style for the images, all I’m using is some border and box-shadow. You might be able to do it better, so feel free to play around with those decorative styles! We’re going to put most of our focus on the animation, which is the trickiest part.

What’s the trick?

The logic of this slider relies on the stacking order of the images — so yes, we are going to play with z-index. All of the images start with the same z-index value (2) which will logically make the last image on the top of the stack.

We take that last image and slide it to the right until it reveals the next image in the stack. Then we decrease the image’s z-index value then we slide it back into the deck. And since its z-index value is lower than the rest of the images, it becomes the last image in the stack.

Here is a stripped back demo that shows the trick. Hover the image to activate the animation:

Now, imagine the same trick applied to all the images. Here’s the pattern if we’re using the :nth-child() pseudo-selector to differentiate the images:

  • We slide the last image (N). The next image is visible (N - 1).
  • We slide the next image (N - 1). The next image is visible (N - 2)
  • We slide the next image (N - 2). The next image is visible (N - 3)
  • (We continue the same process until we reach the first image)
  • We slide the first image (1). The last image (N) is visible again.

That’s our infinite slider!

Dissecting the animation

If you remember the previous article, I defined only one animation and played with delays to control each image. We will be doing the same thing here. Let’s first try to visualize the timeline of our animation. We will start with three images, then generalize it later for any number (N) of images.

Diagramming the three parts of the animation.

Our animation is divided into three parts: “slide to right”, “slide to left” and “don’t move”. We can easily identify the delay between each image. If we consider that the first image starts at 0s, and the duration is equal to 6s, then the second one will start at -2s and the third one at -4s.

.gallery > img:nth-child(2) { animation-delay: -2s; } /* -1 * 6s / 3 */
.gallery > img:nth-child(3) { animation-delay: -4s; } /* -2 * 6s / 3 */

We can also see that the “don’t move” part takes two-thirds of the whole animation (2*100%/3) while the “slide to right” and “slide to left” parts take one-third of it together — so, each one is equal to 100%/6 of the total animation.

We can write our animation keyframes like this:

@keyframes slide {
  0%     { transform: translateX(0%); }
  16.67% { transform: translateX(120%); }
  33.34% { transform: translateX(0%); }
  100%   { transform: translateX(0%); } 
}

That 120% is an arbitrary value. I needed something bigger than 100%. The images need to slide to the right away from the rest of the images. To do that, it needs to move by at least 100% of its size. That’s why I went 120% — to gain some extra space.

Now we need to consider the z-index. Don’t forget that we need to update the image’s z-index value after it slides to the right of the pile, and before we slide it back to the bottom of the pile.

@keyframes slide {
  0%     { transform: translateX(0%);   z-index: 2; }
  16.66% { transform: translateX(120%); z-index: 2; }
  16.67% { transform: translateX(120%); z-index: 1; } /* we update the z-order here */
  33.34% { transform: translateX(0%);   z-index: 1; }
  100%   { transform: translateX(0% );  z-index: 1; }  
}

Instead of defining one state at the 16.67% (100%/6) point in the timeline, we are defining two states at nearly identical points (16.66% and 16.67%) where the z-index value decreases before we slide back the image back to the deck.

Here’s what happens when we pull of all that together:

Hmmm, the sliding part seems to work fine, but the stacking order is all scrambled! The animation starts nicely since the top image is moving to the back… but the subsequent images don’t follow suit. If you notice, the second image in the sequence returns to the top of the stack before the next image blinks on top of it.

We need to closely follow the z-index changes. Initially, all the images have are z-index: 2. That means the stacking order should go…

Our eyes 👀 --> 3rd (2) | 2nd (2) | 1st (2)

We slide the third image and update its z-index to get this order:

Our eyes 👀 --> 2nd (2) | 1st (2) | 3rd (1)

We do the same with the second one:

Our eyes 👀 --> 1st (2) | 3rd (1) | 2nd (1)

…and the first one:

Our eyes 👀 --> 3rd (1) | 2nd (1) | 1st (1)

We do that and everything seems to be fine. But in reality, it’s not! When the first image is moved to the back, the third image will start another iteration, meaning it returns to z-index: 2:

Our eyes 👀 --> 3rd (2) | 2nd (1) | 1st (1)

So, in reality we never had all the images at z-index: 2 at all! When the images aren’t moving (i.e., the “don’t move” part of the animation) the z-index is 1. If we slide the third image and update its z-index value from 2 to 1, it will remain on the top! When all the images have the same z-index, the last one in the source order — our third image in this case — is on top of the stack. Sliding the third image results in the following:

Our eyes 👀 --> 3rd (1) | 2nd (1) | 1st (1)

The third image is still on the top and, right after it, we move the second image to the top when its animation restarts at z-index: 2:

Our eyes 👀 --> 2nd (2) | 3rd (1) | 1st (1)

Once we slide it, we get:

Our eyes 👀 --> 3rd (1) | 2nd (1) | 1st (1)

Then the first image will jump on the top:

Our eyes 👀 --> 1st(2) | 3rd (1) | 2nd (1)

OK, I am lost. All the logic is wrong then?

I know, it’s confusing. But our logic is not completely wrong. We only have to rectify the animation a little to make everything work the way we want. The trick is to correctly reset the z-index.

Let’s take the situation where the third image is on the top:

Our eyes 👀 -->  3rd (2) | 2nd (1) | 1st (1)

We saw that sliding the third image and changing its z-index keeps it on top. What we need to do is update the z-index of the second image. So, before we slide the third image away from the deck, we update the z-index of the second image to 2.

In other words, we reset the z-index of the second image before the animation ends.

Diagramming the parts of the animation with indicators for where z-index is increased or decreased.

The green plus symbol represents increasing z-index to 2, and the red minus symbol correlates to z-index: 1. The second image starts with z-index: 2, then we update it to 1 when it slides away from the deck. But before the first image slides away from the deck, we change the z-index of the second image back to 2. This will make sure both images have the same z-index, but still, the third one will remain on the top because it appears later in the DOM. But after the third image slides and its z-index is updated, it moves to the bottom.

This two-thirds through the animation, so let’s update our keyframes accordingly:

@keyframes slide {
  0%     { transform: translateX(0%);   z-index: 2; }
  16.66% { transform: translateX(120%); z-index: 2; }
  16.67% { transform: translateX(120%); z-index: 1; } /* we update the z-order here */
  33.34% { transform: translateX(0%);   z-index: 1; }
  66.33% { transform: translateX(0%);   z-index: 1; }
  66.34% { transform: translateX(0%);   z-index: 2; } /* and also here */
  100%   { transform: translateX(0%);   z-index: 2; }  
}

A little better, but still not quite there. There’s another issue…

Oh no, this will never end!

Don’t worry, we are not going to change the keyframes again because this issue only happens when the last image is involved. We can make a “special” keyframe animation specifically for the last image to fix things up.

When the first image is on the top, we have the following situation:

Our eyes 👀 -->  1st (2) | 3rd (1) | 2nd (1)

Considering the previous adjustment we made, the third image will jump on the top before the first image slides. It only happens in this situation because the next image that moves after the first image is the last image which has a higher order in the DOM. The rest of the images are fine because we have N, then N - 1, then we go from 3 to 2, and 2 to 1… but then we go from 1 to N.

To avoid that, we will use the following keyframes for the last image:

@keyframes slide-last {
  0%     { transform: translateX(0%);   z-index: 2;}
  16.66% { transform: translateX(120%); z-index: 2; }
  16.67% { transform: translateX(120%); z-index: 1; } /* we update the z-order here */
  33.34% { transform: translateX(0%);   z-index: 1; }
  83.33% { transform: translateX(0%);   z-index: 1; }
  83.34% { transform: translateX(0%);   z-index: 2; } /* and also here */
  100%   { transform: translateX(0%);   z-index: 2; }
}

We reset the z-index value 5/6 through the animation (instead of two-thirds) which is when the first image is out of the pile. So we don’t see any jumping!

TADA! Our infinite slider is now perfect! Here’s our final code in all its glory:

.gallery > img {
  animation: slide 6s infinite;
}
.gallery > img:last-child {
  animation-name: slide-last;
}
.gallery > img:nth-child(2) { animation-delay: -2s; } 
.gallery > img:nth-child(3) { animation-delay: -4s; }

@keyframes slide {
  0% { transform: translateX(0%); z-index: 2; }
  16.66% { transform: translateX(120%); z-index: 2; }
  16.67% { transform: translateX(120%); z-index: 1; } 
  33.34% { transform: translateX(0%); z-index: 1; }
  66.33% { transform: translateX(0%); z-index: 1; }
  66.34% { transform: translateX(0%); z-index: 2; } 
  100% { transform: translateX(0%); z-index: 2; }
}
@keyframes slide-last {
  0% { transform: translateX(0%); z-index: 2; }
  16.66% { transform: translateX(120%); z-index: 2; }
  16.67% { transform: translateX(120%); z-index: 1; }
  33.34% { transform: translateX(0%); z-index: 1; }
  83.33% { transform: translateX(0%); z-index: 1; }
  83.34% { transform: translateX(0%); z-index: 2; } 
  100%  { transform: translateX(0%); z-index: 2; }
}

Supporting any number of images

Now that our animation works for three images, let’s make it work for any number (N) of images. But first, we can optimize our work a little by splitting the animation up to avoid redundancy:

.gallery > img {
  z-index: 2;
  animation: 
    slide 6s infinite,
    z-order 6s infinite steps(1);
}
.gallery > img:last-child {
  animation-name: slide, z-order-last;
}
.gallery > img:nth-child(2) { animation-delay: -2s; } 
.gallery > img:nth-child(3) { animation-delay: -4s; }

@keyframes slide {
  16.67% { transform: translateX(120%); }
  33.33% { transform: translateX(0%); }
}
@keyframes z-order {
  16.67%,
  33.33% { z-index: 1; }
  66.33% { z-index: 2; }
}
@keyframes z-order-last {
  16.67%,
  33.33% { z-index: 1; }
  83.33% { z-index: 2; }
}

Way less code now! We make one animation for the sliding part and another one for the z-index updates. Note that we use steps(1) on the z-index animation. That’s because I want to abruptly change the z-index value, unlike the sliding animation where we want smooth movement.

Now that the code is easier to read and maintain, we have a better view for figuring out how to support any number of images. What we need to do is update the animation delays and the percentages of the keyframes. The delay are easy because we can use the exact same loop we made in the last article to support multiple images in the circular slider:

@for $i from 2 to ($n + 1) {
  .gallery > img:nth-child(#{$i}) {
    animation-delay: calc(#{(1 - $i)/$n}*6s);
  }
}

That means we’re moving from vanilla CSS to Sass. Next, we need to imagine how the timeline scale with N images. Let’s not forget that the animation happens in three phases:

Showing the three parts of the animation in a series of lines with arrows.

After “slide to right” and “slide to left”, the image should stay put until the rest of the images go through the sequence. So the “don’t move” part needs to take the same amount of time as (N - 1) as “slide to right” and “slide to left”. And within one iteration, N images will slide. So, “slide to right” and “slide to left” both take 100%/N of the total animation timeline. The image slides away from the pile at (100%/N)/2 and slides back at 100%/N .

We can change this:

@keyframes slide {
  16.67% { transform: translateX(120%); }
  33.33% { transform: translateX(0%); }
}

…to this:

@keyframes slide {
  #{50/$n}%  { transform: translateX(120%); }
  #{100/$n}% { transform: translateX(0%); }
}

If we replace N with 3, we get 16.67% and 33.33% when there are 3 images in the stack. It’s the same logic with the stacking order where we will have this:

@keyframes z-order {
  #{50/$n}%,
  #{100/$n}% { z-index: 1; }
  66.33% { z-index: 2; }
}

We still need to update the 66.33% point. That’s supposed to be where the image resets its z-index before the end of the animation. At that same time, the next image starts to slide. Since the sliding part takes 100%/N, the reset should happen at 100% - 100%/N:

@keyframes z-order {
  #{50/$n}%,
  #{100/$n}% { z-index: 1; }
  #{100 - 100/$n}% { z-index: 2; }
}

But for our z-order-last animation to work, it should happen a bit later in the sequence. Remember the fix we did for the last image? Resetting the z-index value needs to happen when the first image is out of the pile and not when it starts sliding. We can use the same reasoning here in our keyframes:

@keyframes z-order-last {
  #{50/$n}%,
  #{100/$n}% { z-index: 1; }
  #{100 - 50/$n}% { z-index: 2; }
}

We are done! Here’s what we get when using five images:

We can add a touch of rotation to make things a bit fancier:

All I did is append rotate(var(--r)) to the transform property. Inside the loop, --r is defined with a random angle:

@for $i from 1 to ($n + 1) {
  .gallery > img:nth-child(#{$i}) {
    --r: #{(-20 + random(40))*1deg}; /* a random angle between -20deg and 20deg */
  }
}

The rotation creates small glitches as we can sometimes see some of the images jumping to the back of the stack, but it’s not a big deal.

Wrapping up

All that z-index work was a big balancing act, right? If you were unsure how stacking order work before this exercise, then you probably have a much better idea now! If you found some of the explanations hard to follow, I highly recommend you to take another read of the article and map things out with pencil and paper. Try to illustrate each step of the animation using a different number of images to better understand the trick.

Last time, we used a few geometry tricks to create a circular slider that rotates back to the first image after a full sequence. This time, we accomplished a similar trick using z-index. In both cases, we didn’t duplicate any of the images to simulate a continuous animation, nor did we reach for JavaScript to help with the calculations.

Next time, we will make 3D sliders. Stay tuned!


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CSS Infinite and Circular Rotating Image Slider https://css-tricks.com/css-only-infinite-and-circular-image-slider/ https://css-tricks.com/css-only-infinite-and-circular-image-slider/#comments Fri, 02 Dec 2022 14:12:57 +0000 https://css-tricks.com/?p=375308 Image sliders (also called carousels) are everywhere. There are a lot of CSS tricks to create the common slider where the images slide from left to right (or the opposite). It’s the same deal with the many JavaScript libraries out


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Image sliders (also called carousels) are everywhere. There are a lot of CSS tricks to create the common slider where the images slide from left to right (or the opposite). It’s the same deal with the many JavaScript libraries out there that create fancy sliders with complex animations. We are not going to do any of that in this post.

Through a little series of articles, we are going to explore some fancy and uncommon CSS-only sliders. If you are of tired seeing the same ol’ classic sliders, then you are in the right place!

For this first article, we will start with something I call the “circular rotating image slider”:

Cool right? let’s dissect the code!

The HTML markup

If you followed my series of fancy image decorations or CSS grid and custom shapes, then you know that my first rule is to work with the smallest HTML possible. I always try hard to find CSS solutions before cluttering my code with a lot <div>s and other stuff.

The same rule applies here — our code is nothing but a list of images in a container.

Let’s say we’re working with four images:

<div class="gallery">
  <img src="" alt="">
  <img src="" alt="">
  <img src="" alt="">
  <img src="" alt="">
</div>

That’s it! Now let’s move to the interesting part of the code. But first, we’re going to dive into this to understand the logic of how our slider works.

How does it work?

Here is a video where I remove overflow: hidden from the CSS so we can better understand how the images are moving:

It’s like our four images are placed on a large circle that rotates counter-clockwise.

All the images have the same size (denoted by S in the figure). Note the blue circle which is the circle that intersects with the center of all the images and has a radius (R). We will need this value later for our animation. R is equal to 0.707 * S. (I’m going to skip the geometry that gives us that equation.)

Let’s write some CSS!

We will be using CSS Grid to place all the images in the same area above each other:

.gallery  {
  --s: 280px; /* control the size */

  display: grid;
  width: var(--s);
  aspect-ratio: 1;
  padding: calc(var(--s) / 20); /* we will see the utility of this later */
  border-radius: 50%;
}
.gallery > img {
  grid-area: 1 / 1;
  width: 100%;
  height: 100%;
  object-fit: cover;
  border-radius: inherit;
}

Nothing too complex so far. The tricky part is the animation.

We talked about rotating a big circle, but in reality, we will rotate each image individually creating the illusion of a big rotating circle. So, let’s define an animation, m, and apply it to the image elements:

.gallery > img {
  /* same as before */
  animation: m 8s infinite linear;
  transform-origin: 50% 120.7%;
}

@keyframes m {
  100% { transform: rotate(-360deg); }
}

The main trick relies on that highlighted line. By default, the CSS transform-origin property is equal to center (or 50% 50%) which makes the image rotate around its center, but we don’t need it to do that. We need the image to rotate around the center of the big circle that contains our images hence the new value for transform-origin.

Since R is equal to 0.707 * S, we can say that R is equal to 70.7% of the image size. Here’s a figure to illustrate how we got the 120.7% value:

Let’s run the animation and see what happens:

I know, I know. The result is far from what we want, but in reality we are very close. It may looks like there’s just one image there, but don’t forget that we have stacked all the images on top of each other. All of them are rotating at the same time and only the top image is visible. What we need is to delay the animation of each image to avoid this overlap.

.gallery > img:nth-child(2) { animation-delay: -2s; } /* -1 * 8s / 4 */
.gallery > img:nth-child(3) { animation-delay: -4s; } /* -2 * 8s / 4 */
.gallery > img:nth-child(4) { animation-delay: -6s; } /* -3 * 8s / 4 */

Things are already getting better!

If we hide the overflow on the container we can already see a slider, but we will update the animation a little so that each image remains visible for a short period before it moves along.

We’re going to update our animation keyframes to do just that:

@keyframes m {
  0%, 3% { transform: rotate(0); }
  22%, 27% { transform: rotate(-90deg); }
  47%, 52% { transform: rotate(-180deg); }
  72%, 77% { transform: rotate(-270deg); }
  98%, 100% { transform: rotate(-360deg); }
}

For each 90deg (360deg/4, where 4 is the number of images) we will add a small pause. Each image will remain visible for 5% of the overall duration before we slide to the next one (27%-22%, 52%-47%, etc.). I’m going to update the animation-timing-function using a cubic-bezier() function to make the animation a bit fancier:

Now our slider is perfect! Well, almost perfect because we are still missing the final touch: the colorful circular border that rotates around our images. We can use a pseudo-element on the .gallery wrapper to make it:

.gallery {
  padding: calc(var(--s) / 20); /* the padding is needed here */
  position: relative;
}
.gallery::after {
  content: "";
  position: absolute;
  inset: 0;
  padding: inherit; /* Inherits the same padding */
  border-radius: 50%;
  background: repeating-conic-gradient(#789048 0 30deg, #DFBA69 0 60deg);
  mask: 
    linear-gradient(#fff 0 0) content-box, 
    linear-gradient(#fff 0 0);
  mask-composite: exclude;
}
.gallery::after,
.gallery >img {
  animation: m 8s infinite cubic-bezier(.5, -0.2, .5, 1.2);
}

I have created a circle with a repeating conic gradient for the background while using a masking trick that only shows the padded area. Then I apply to it the same animation we defined for the images.

We are done! We have a cool circular slider:

Let’s add more images

Working with four images is good, but it would be better if we can scale it to any number of images. After all, this is the purpose of an image slider. We should be able to consider N images.

For this, we are going to make the code more generic by introducing Sass. First, we define a variable for the number of images ($n) and we will update every part where we hard-coded the number of images (4).

Let’s start with the delays:

.gallery > img:nth-child(2) { animation-delay: -2s; } /* -1 * 8s / 4 */
.gallery > img:nth-child(3) { animation-delay: -4s; } /* -2 * 8s / 4 */
.gallery > img:nth-child(4) { animation-delay: -6s; } /* -3 * 8s / 4 */

The formula for the delay is (1 - $i)*duration/$n, which gives us the following Sass loop:

@for $i from 2 to ($n + 1) {
  .gallery > img:nth-child(#{$i}) {
    animation-delay: calc(#{(1 - $i) / $n} * 8s);
  }
}

We can make the duration a variable as well if we really want to. But let’s move on to the animation:

@keyframes m {
  0%, 3% { transform: rotate(0); }
  22%, 27% { transform: rotate(-90deg); }
  47%, 52% { transform: rotate(-180deg); }
  72%, 77% { transform: rotate(-270deg); }
  98%, 100% {transform: rotate(-360deg); }
}

Let’s simplify it to get a better view of the pattern:

@keyframes m {
  0% { transform: rotate(0); }
  25% { transform: rotate(-90deg); }
  50% { transform: rotate(-180deg); }
  75% { transform: rotate(-270deg); }
  100% { transform: rotate(-360deg); }
}

The step between each state is equal to 25% — which is 100%/4 — and we add a -90deg angle — which is -360deg/4. That means we can write our loop like this instead:

@keyframes m {
  0% { transform: rotate(0); }
  @for $i from 1 to $n {
    #{($i / $n) * 100}% { transform: rotate(#{($i / $n) * -360}deg); }  
  }
  100% { transform: rotate(-360deg); }
}

Since each image takes 5% of the animation, we change this:

#{($i / $n) * 100}%

…with this:

#{($i / $n) * 100 - 2}%, #{($i / $n) * 100 + 3}%

It should be noted that 5% is an arbitrary value I choose for this example. We can also make it a variable to control how much time each image should stay visible. I am going to skip that for the sake of simplicity, but for homework, you can try to do it and share your implementation in the comments!

@keyframes m {
  0%,3% { transform: rotate(0); }
  @for $i from 1 to $n {
    #{($i / $n) * 100 - 2}%, #{($i / $n) * 100 + 3}% { transform: rotate(#{($i / $n) * -360}deg); }  
  }
  98%,100% { transform: rotate(-360deg); }
}

The last bit is to update transform-origin. We will need some geometry tricks. Whatever the number of images, the configuration is always the same. We have our images (small circles) placed inside a big circle and we need to find the value of the radius, R.

You probably don’t want a boring geometry explanation so here’s how we find R:

R = S / (2 * sin(180deg / N))

If we express that as a percentage, that gives us:

R = 100% / (2 * sin(180deg / N)) = 50% / sin(180deg / N)

…which means the transform-origin value is equal to:

transform-origin: 50% (50% / math.sin(180deg / $n) + 50%);

We’re done! We have a slider that works with any number images!

Let’s toss nine images in there:

Add as many images as you want and update the $n variable with the total number of images.

Wrapping up

With a few tricks using CSS transforms and standard geometry, we created a nice circular slider that doesn’t require a lot of code. What is cool about this slider is that we don’t need to bother duplicating the images to keep the infinite animation since we have a circle. After a full rotation, we will get back to the first image!


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Making Static Noise From a Weird CSS Gradient Bug https://css-tricks.com/making-static-noise-from-a-weird-css-gradient-bug/ https://css-tricks.com/making-static-noise-from-a-weird-css-gradient-bug/#comments Fri, 18 Nov 2022 13:55:24 +0000 https://css-tricks.com/?p=374993 What I will be doing here is kind of an experiment to explore tricks that leverage a bug with the way CSS gradients handle sub-pixel rendering to create a static noise effect — like you might see on a TV with no signal.


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👋 The demos in this article experiment with a non-standard bug related to CSS gradients and sub-pixel rendering. Their behavior may change at any time in the future. They’re also heavy as heck. We’re serving them async where you click to load, but still want to give you a heads-up in case your laptop fan starts spinning.

Do you remember that static noise on old TVs with no signal? Or when the signal is bad and the picture is distorted? In case the concept of a TV signal predates you, here’s a GIF that shows exactly what I mean.

View image (contains auto-playing media)
Animated image showing static noise from a TV screen.

Yes, we are going to do something like this using only CSS. Here is what we’re making:

Before we start digging into the code, I want to say that there are better ways to create a static noise effect than the method I am going to show you. We can use SVG, <canvas>, the filter property, etc. In fact, Jimmy Chion wrote a good article showing how to do it with SVG.

What I will be doing here is kind of a CSS experiment to explore some tricks leveraging a bug with gradients. You can use it on your side projects for fun but using SVG is cleaner and more suitable for a real project. Plus, the effect behaves differently across browsers, so if you’re checking these out, it’s best to view them in Chrome, Edge, or Firefox.

Let’s make some noise!

To make this noise effect we are going to use… gradients! No, there is no secret ingredient or new property that makes it happen. We are going to use stuff that’s already in our CSS toolbox!

The “trick” relies on the fact that gradients are bad at anti-aliasing. You know those kind of jagged edges we get when using hard stop colors? Yes, I talk about them in most of my articles because they are a bit annoying and we always need to add or remove a few pixels to smooth things out:

As you can see, the second circle renders better than the first one because there is a tiny difference (0.5%) between the two colors in the gradient rather than using a straight-up hard color stop using whole number values like the first circle.

Here’s another look, this time using a conic-gradient where the result is more obvious:

An interesting idea struck me while I was making these demos. Instead of fixing the distortion all the time, why not trying to do the opposite? I had no idea what would happen but it was a fun surprise! I took the conic gradient values and started to decrease them to make the poor anti-aliasing results look even worse.

Do you see how bad the last one is? It’s a kind of scrambled in the middle and nothing is smooth. Let’s make it full-screen with smaller values:

I suppose you see where this is going. We get a strange distorted visual when we use very small decimal values for the hard colors stops in a gradient. Our noise is born!

We are still far from the grainy noise we want because we can still see the actual conic gradient. But we can decrease the values to very, very small ones — like 0.0001% — and suddenly there’s no more gradient but pure graininess:

Tada! We have a noise effect and all it takes is one CSS gradient. I bet if I was to show this to you before explaining it, you’d never realize you’re looking at a gradient. You have to look very carefully at center of the gradient to see it.

We can increase the randomness by making the size of the gradient very big while adjusting its position:

The gradient is applied to a fixed 3000px square and placed at the 60% 60% coordinates. We can hardly notice its center in this case. The same can be done with radial gradient as well:

And to make things even more random (and closer to a real noise effect) we can combine both gradients and use background-blend-mode to smooth things out:

Our noise effect is perfect! Even if we look closely at each example, there’s no trace of either gradient in there, but rather beautiful grainy static noise. We just turned that anti-aliasing bug into a slick feature!

Now that we have this, let’s see a few interesting examples where we might use it.

Animated no TV signal

Getting back to the demo we started with:

If you check the code, you will see that I am using a CSS animation on one of the gradients. It’s really as simple as that! All we’re doing is moving the conic gradient’s position at a lightning fast duration (.1s) and this is what we get!

I used this same technique on a one-div CSS art challenge:

Grainy image filter

Another idea is to apply the noise to an image to get an old-time-y look. Hover each image to see them without the noise.

I am using only one gradient on a pseudo-element and blending it with the image, thanks to mix-blend-mode: overlay.

We can get an even funnier effect if we use the CSS filter property

And if we add a mask to the mix, we can make even more effects!

Grainy text treatment

We can apply this same effect to text, too. Again, all we need is a couple of chained gradients on a background-image and then blend the backgrounds. The only difference is that we’re also reaching for background-clip so the effect is only applied to the bounds of each character.

Generative art

If you keep playing with the gradient values, you may get more surprising results than a simple noise effect. We can get some random shapes that look a lot like generative art!

Of course, we are far from real generative art, which requires a lot of work. But it’s still satisfying to see what can be achieved with something that is technically considered a bug!

Monster face

One last example I made for CodePen’s divtober 2022 collection:

Wrapping up

I hope you enjoyed this little CSS experiment. We didn’t exactly learn something “new” but we took a little quirk with gradients and turned it into something fun. I’ll say it again: this isn’t something I would consider using on a real project because who knows if or when anti-aliasing will be addressed at some point in time. Instead, this was a very random, and pleasant, surprise when I stumbled into it. It’s also not that easy to control and it behaves inconsistently across browsers.

This said, I am curious to see what you can do with it! You can play with the values, combine different layers, use a filter, or mix-blend-mode, or whatever, and you will for sure get something really cool. Share your creations in the comment section — there are no prizes but we can get a nice collection going!


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CSS Grid and Custom Shapes, Part 3 https://css-tricks.com/css-grid-and-custom-shapes-part-3/ https://css-tricks.com/css-grid-and-custom-shapes-part-3/#comments Fri, 11 Nov 2022 14:42:04 +0000 https://css-tricks.com/?p=374826 After Part 1 and Part 2, I am back with a third article to explore more fancy shapes. Like the previous articles, we are going to combine CSS Grid with clipping and masking to create fancy layouts for image …


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After Part 1 and Part 2, I am back with a third article to explore more fancy shapes. Like the previous articles, we are going to combine CSS Grid with clipping and masking to create fancy layouts for image galleries.

CSS Grid and Custom Shapes series

Should I read the previous articles before?

It’s not mandatory but highly recommended to cover as many tricks as possible. You can also read them in any order, but following along in chronological is a good idea to see how we arrived here.

Enough talking, let’s jump straight to our first example.

Before digging into the CSS, let’s check the markup:

<div class="gallery">
  <img src="..." alt="...">
  <img src="..." alt="...">
  <img src="..." alt="...">
  <img src="..." alt="...">
</div>

Nothing but a few <img> tags in a div wrapper, right? Remember, the main challenge for this series is to work with the smallest amount of HTML possible. All the examples we’ve seen throughout this series use the exact same HTML markup. No extra divs, wrappers, and whatnot. All that we need are images contained in a wrapper element.

Let’s check the CSS now:

.gallery {
  --g: 6px; /* the gap */

  display: grid;
  width: 450px; /* the size */
  aspect-ratio: 1; /* equal height */
  grid: auto-flow 1fr / repeat(3, 1fr);
  gap: var(--g);
}
.gallery img:nth-child(2) {
  grid-area: 1 / 2 / span 2 / span 2;
}
.gallery img:nth-child(3) {
  grid-area: 2 / 1 / span 2 / span 2;
}

Basically, this is a square grid with three equal columns. From there, all that’s happening is the second and third images are explicitly placed on the grid, allowing the first and last images to lay out automatically around them.

This automatic behavior is a powerful feature of CSS Grid called “auto-placement”. Same thing with the number of rows — none of them are explicitly defined. The browser “implicitly” creates them based on the placement of the items. I have a very detailed article that explores both concepts.

You might be wondering what’s going on with those grid and grid-area property values. They look strange and are tough to grok! That’s because I chose the CSS grid shorthand property, which is super useful but accepts an unseemly number of values from its constituent properties. You can see all of them in the Almanac.

But what you really need to know is this:

grid: auto-flow 1fr / repeat(3, 1fr);

…is equivalent to this:

grid-template-columns: repeat(3, 1fr);
grid-auto-rows: 1fr;
DevTools style rules for the grid property.
You can also use your favorite DevTools for further proof.

Same for the grid-area property. If we open DevTools and inspect our declaration: grid-area: 1/2/span 2/span 2; you will get the following:

grid-area: 1 / 2 / span 2 / span 2;

…that is the same as writing all this out:

grid-row-start: 1; /* 1st row */
grid-column-start: 2; /* 2nd column */
grid-row-end: span 2; /* take 2 rows */
grid-column-end: span 2; /* take 2 columns */

Same deal for the other grid-area declaration. When we put it all together, here’s what we get:

The different images labeled by number on the grid.

Yes, the second and third images are overlapped in the middle. That’s no mistake! I purposely spanned them on top of one another so that I can apply a clip-path to cut a portion from each one and get the final result:

Showing the effect with and without clip-path.

How do we do that? We can cut the bottom-left corner of the second image (img:nth-child(2)) with the CSS clip-path property:

clip-path: polygon(0 0, 100% 0, 100% 100%, calc(50% + var(--g) / 4) 100%, 0 calc(50% - var(--g) / 4))

And the top-right corner of the third one:

clip-path: polygon(0 0, calc(50% - var(--g) / 4) 0, 100% calc(50% + var(--g) / 4), 100% 100%, 0 100%);

I know, I know. That’s a lot of numbers and whatnot. I do have an article that details the technique.

That’s it, we have our first grid of images! I added a grayscale filter on the <img> selector to get that neat little hover effect.

The Split Image Reveal

Let’s try something different. We can take what we learned about clipping the corner of an image and combine it with a nice effect to reveal the full image on hover.

The grid configuration for this one is less intense than the last one, as all we need are two overlapping images:

.gallery {
  display: grid;
}
.gallery > img {
  grid-area: 1 / 1;
  width: 350px; /* the size */
  aspect-ratio: 1; /* equal height */
}

Two images that are the same size are stacked on top of each other (thanks to grid-area: 1 / 1).

The hover effect relies on animating clip-path. We will dissect the code of the first image to see how it works, then plug the same thing into the second image with updated values. Notice, though that we have three different states:

  1. When no images are hovered, half of each image is revealed.
  2. When we hover over the first image, it is more fully revealed but retains a small corner clip.
  3. When we hover over the second image, the first one has only a small triangle visible.
Showing the three clipping states of the hover effect.

In each case, we have a triangular shape. That means we need a three-point polygon for the clip-path value.

What? The second state isn’t a triangle, but more of a square with a cut corner.

You are right, but if we look closely we can see a “hidden” triangle. Let’s add a box-shadow to the images.

A ha! Did you notice it?

Showing the transition between states with the overflow shape revealed to explain how it works.

What sort of magic is this? It’s a little known fact that clip-path accepts values outside the 0%-100% range, which allows us to create “overflowing” shapes. (Yes, I just coined this. You’re welcome.) This way, we only have to work with three points instead of the five it would take to make the same shape from the visible parts. Optimized CSS for the win!

This is the code after we plug in the polygon values into the clip-path property:

.gallery > img:first-child {
  clip-path: polygon(0 0, calc(100% + var(--_p)) 0 , 0 calc(100% + var(--_p)))
}
.gallery > img:last-child {
  clip-path: polygon(100% 100%, 100% calc(0% - var(--_p)), calc(0% - var(--_p)) 100%)
}

Notice the --_p variable. I’m using that to optimize the code a bit as we add the hover transition. Instead of updating the whole clip-path we only update this variable to get the movement. Here is a video to see how the points should move between each state:

We can take slap a transition on the <img> selector, then update the --_p variable on the states to get the final effect:

.gallery {
  --g: 8px; /* the gap */
}
.gallery > img {
  /* etc. */
  --_p: calc(-1 * var(--g));
  transition: .4s .1s;
}
.gallery:hover > img:last-child,
.gallery:hover > img:first-child:hover{
  --_p: calc(50% - var(--g));
}
.gallery:hover > img:first-child,
.gallery:hover > img:first-child:hover + img {
  --_p: calc(-50% - var(--g));
}

If we don’t consider the gap (defined as --g in the code) between the images, then the three values of --_p are 0%, 50%, and -50%. Each one defines one of the states we explained previously.

The Pie Image Reveal

Let’s increase the difficulty level from that last one and try to do the same trick but with four images instead of two.

Cool, right? Each image is a quarter of a circle and, on hover, we have an animation that transforms an image into a full circle that covers the remaining images. The effect may look impossible because there is no way to rotate points and transform them to fill the circle. In reality, though, we are not rotating any points at all. It’s an illusion!

For this example, I will only focus on the clip-path animation since the configuration of the grid is the same as the previous example: four equally-sized images stacked on top of each other.

And a video worth a boring and long explanation:

The clip-path is formed by seven points, where three of them are in a fixed position and the others move as shown in the video. The effect looks less cool when it’s running slowly but we can see how the clip-path morphs between shapes.

The effect is a little better if we add border-radius and we make it faster:

And by making it even faster like in the original example, we get the perfect illusion of one quarter of a circle morphing into a full circle. Here’s the polygon value for our clip-path on the first image in the sequence:

.gallery > img:nth-child(1) {
  clip-path: polygon(50% 50%, calc(50% * var(--_i, 0)) calc(120% * var(--_i, 0)), 0 calc(100% * var(--_i, 0)),0 0, 100% 0, 100% calc(100% * var(--_i, 0)), calc(100% - 50% * var(--_i, 0)) calc(120% * var(--_i, 0)));
}
.gallery > img:hover {
 --_i: 1;
}

As usual, I am using a variable to optimize the code. The variable will switch between 0 and 1 to update the polygon.

The same goes for the others image but with a different clip-path configuration. I know that the values may look hard to decipher but you can always use online tools like Clippy to visualize the values.

The Mosaic of Images

You know mosaics, right? It’s an art style that creates decorative designs out of smaller individual pieces, like colored stones. But it can also be a composite image made up of other smaller images.

And, you guessed it: we can totally do that sort of thing in CSS!

First, let’s imagine what things are like if clip-path were taken out of the mix and all we had were five overlapping images:

I am cheating a little in this video because I am inspecting the code to identify the area of each image, but this is what you need to do in your head. For each image, try to complete the missing part to see the full rectangle and, with this, we can identify the position and size of each one.

We need to find how many columns and rows we need for the grid:

  1. We have two big images placed next to each other that each fill half the grid width and the full grid height. That means will probably need two columns (one for both images) and one row (for the full height of the grid).
  2. We have the image in the middle that overlaps the two other images. That means we actually need four columns instead of two, though we still only need the one row.
  3. The last two images each fill half the grid, just like the first two images. But they’re only half the height of the grid. We can use the existing columns we already have, but we’re going to need two rows instead of one to account for these images being half the grid height.
That leaves us with a tidy 4×2 grid.

I don’t want you to think that the way I sliced this up is the only way to do it. This is merely how I’ve made sense of it. I am sure there are other configurations possible to get the same layout!

Let’s take that information and define our grid, then place the images on it:

.gallery {
  display: grid;
  grid: repeat(2, 1fr) / repeat(4, 1fr); 
  aspect-ratio: 2;
}
.gallery img:nth-child(1) {
  grid-area: 1 / 1 / span 2 / span 2;
}
.gallery img:nth-child(2) {
  grid-area: 1 / 2 / span 2 / span 2;
}
.gallery img:nth-child(3) {
  grid-area: span 2 / span 2 / -1 / -1;
}
.gallery img:nth-child(4) {
  grid-area: 2 / 1 / span 1 / span 2;
}
.gallery img:nth-child(5) {
  grid-area: span 1 / span 2 / -1 / -1;
}

I think you get the idea of what’s happening here now that we’ve seen a few examples using the same approach. We define a grid and place images on it explicitly, using grid-area so the images overlap.

OK, but the aspect-ratio is different this time.

It is! If you get back to the reasoning we made, we have the first two images that are square next to each other having the same size. This means that the width of the grid needs to be equal to twice its height. Hence, aspect-ratio: 2.

Now it’s time for the clip-path values. We have four triangles and a rhombus.

Showing the three unique shapes and the clip-path values that create them.
We’re only showing the three unique shapes we’re making instead of the five total shapes.

Again, I’m using Clippy for all this math-y stuff. But, honestly, I can write many simple shapes by hand, having spent several years working closely with clip-path, and I know you can too with practice!

The Complex Mosaic of Images

Let’s increase the difficulty and try another mosaic, this time with less symmetry and more complex shapes.

Don’t worry, you will see that it’s the same concept as the one we just made! Again, let’s imagine each image is a rectangle, then go about defining the grid based on what we see.

We’ll start with two images:

They are both squares. The first image is equal to half the size of the second image. The first image takes up less than one half of the grid width, while the second image takes up more than half giving us a total of two columns with a different size (the first one is equal to half the second one). The first image is half the height, so let’s automatically assume we need two rows as well.

Let’s add another image to the layout

This one makes things a bit more complex! We need to draw some lines to identify how to update the grid configuration.

We will move from a 2×2 grid to four columns and three rows. Pretty asymmetric, right? Before we try to figure out that complete sizing, let’s see if the same layout holds up when we add the other images.

Looks like we still need more rows and columns for everything to fall into place. Based on the lines in that image, we’re going to have a total of five columns and four rows.

The logic is simple even though the layout is complex, right? We add the images one by one to find the right configuration that fits everything. Now we need to identify the size of each column and row.

If we say the smallest row/column is equal to one fraction of the grid (1fr) we will get:

grid-template-columns: 1fr 1fr 2fr 3fr 5fr;

…for the columns, and:

grid-template-rows: 3fr 1fr 2fr 2fr;

…for the rows. We can consolidate this using the grid shorthand property again:

grid: 3fr 1fr 2fr 2fr / 1fr 1fr 2fr 3fr 5fr;

You know the drill! Place the images on the grid and apply a clip-path on them:

.gallery img:nth-child(1) {
  grid-area: 1 / 1 /span 2 / span 3;
  clip-path: polygon(0 0, 100% 0, 0 100%);
}
.gallery img:nth-child(2) {
  grid-area: 1/2/span 3/span 3;
  clip-path: polygon(50% 0, 100% 50%, 50% 100%, 0 50%);
}
.gallery img:nth-child(3) {
  grid-area: 1 / span 2 / -1 / -1;
  clip-path: polygon(0 0, 100% 0, 100% 100%);
}
.gallery img:nth-child(4) {
  grid-area: span 3 / 1 / -1 / span 3;
  clip-path: polygon(25% 0, 100% 60%, 50% 100%, 0 100%, 0 20%);
}
.gallery img:nth-child(5) {
  grid-area: span 3/span 3/-1/-1;
  clip-path: polygon(50% 0, 100% 100%, 0 100%);
}

We can stop here and our code is fine, but we will do a little more to optimize the clip-path values. Since we don’t have any gaps between our images, we can use the fact that our images overlap to slim things down. Here is a video to illustrate the idea:

As you can see, the image in the middle (the one with the camera) doesn’t need a clip-path. because the other images overlap it, giving us the shape without any additional work! And notice that we can use the same overflowing three-point clip-path concept we used earlier on the image in the bottom-left to keep the code smaller there as well.

In the end, we have a complex-looking grid of images with only four clip-path declarations — all of them are three-point polygons!

Wrapping up

Wow, right? I don’t know about you, but I never get bored of seeing what CSS can do these days. It wasn’t long ago that all of this would have taken verbose hackery and definitely some JavaScript.

Throughout this series, we explored many, many different types of image grids, from the basic stuff to the complex mosaics we made today. And we got a lot of hands-on experience working with CSS clipping — something that you will definitely be able to use on other projects!

But before we end this, I have some homework for you…

Here are two mosaics that I want you to make using what we covered here. One is on the “easier” side, and the other is a bit tricky. It would be really awesome to see your work in the comments, so link them up! I’m curious to see if your approach is different from how I’d go about it!


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Fancy Image Decorations: Outlines and Complex Animations https://css-tricks.com/fancy-image-decorations-outlines-and-complex-animations/ https://css-tricks.com/fancy-image-decorations-outlines-and-complex-animations/#comments Fri, 28 Oct 2022 12:45:47 +0000 https://css-tricks.com/?p=374302 We’ve spent the last two articles in this three-part series playing with gradients to make really neat image decorations using nothing but the <img> element. In this third and final piece, we are going to explore more techniques using the …


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We’ve spent the last two articles in this three-part series playing with gradients to make really neat image decorations using nothing but the <img> element. In this third and final piece, we are going to explore more techniques using the CSS outline property. That might sound odd because we generally use outline to draw a simple line around an element — sorta like border but it can only draw all four sides at once and is not part of the Box Model.

We can do more with it, though, and that’s what I want to experiment with in this article.

Fancy Image Decorations series

Let’s start with our first example — an overlay that disappears on hover with a cool animation:

We could accomplish this by adding an extra element over the image, but that’s what we’re challenging ourselves not to do in this series. Instead, we can reach for the CSS outline property and leverage that it can have a negative offset and is able to overlap its element.

img {
  --s: 250px; /* the size of the image */
  --b: 8px;   /* the border thickness*/
  --g: 14px;  /* the gap */
  --c: #4ECDC4;

  width: var(--s);
  aspect-ratio: 1;
  outline: calc(var(--s) / 2) solid #0009;
  outline-offset: calc(var(--s) / -2);
  cursor: pointer;
  transition: 0.3s;
}
img:hover {
  outline: var(--b) solid var(--c);
  outline-offset: var(--g);
}

The trick is to create an outline that’s as thick as half the image size, then offset it by half the image size with a negative value. Add in some semi-transparency with the color and we have our overlay!

Diagram showing the size of the outline sround the image and how it covers the image on hover.

The rest is what happens on :hover. We update the outline and the transition between both outlines creates the cool hover effect. The same technique can also be used to create a fading effect where we don’t move the outline but make it transparent.

Instead of using half the image size in this one, I am using a very big outline thickness value (100vmax) while applying a CSS mask. With this, there’s no longer a need to know the image size — it trick works at all sizes!

Diagram showing how adding a mask clips the extra outline around the image.

You may face issues using 100vmax as a big value in Safari. If it’s the case, consider the previous trick where you replace the 100vmax with half the image size.

We can take things even further! For example, instead of simply clipping the extra outline, we can create shapes and apply a fancy reveal animation.

Cool right? The outline is what creates the yellow overlay. The clip-path clips the extra outline to get the star shape. Then, on hover, we make the color transparent.

Oh, you want hearts instead? We can certainly do that!

Imagine all the possible combinations we can create. All we have to do is to draw a shape with a CSS mask and/or clip-path and combine it with the outline trick. One solution, infinite possibilities!

And, yes, we can definitely animate this as well. Let’s not forget that clip-path is animatable and mask relies on gradients — something we covered in super great detail in the first two articles of this series.

I know, the animation is a bit glitchy. This is more of a demo to illustrate the idea rather than the “final product” to be used in a production site. We’d wanna optimize things for a more natural transition.

Here is a demo that uses mask instead. It’s the one I teased you with at the end of the last article:

Did you know that the outline property was capable of so much awesomeness? Add it to your toolbox for fancy image decorations!

Combine all the things!

Now that we have learned many tricks using gradients, masks, clipping, and outline, it’s time for the grand finale. Let’s cap off this series by combine all that we have learned the past few weeks to showcase not only the techniques, but demonstrate just how flexible and modular these approaches are.

If you were seeing these demos for the first time, you might assume that there’s a bunch of extra divs wrappers and pseudo-elements being used to pull them off. But everything is happening directly on the <img> element. It’s the only selector we need to get these advanced shapes and effects!

Wrapping up

Well, geez, thanks for hanging out with me in this three-part series the past few weeks. We explored a slew of different techniques that turn simple images into something eye-catching and interactive. Will you use everything we covered? Certainly not! But my hope is that this has been a good exercise for you to dig into advanced uses of CSS features, like gradients, mask, clip-path, and outline.

And we did everything with just one <img> element! No extra div wrappers and pseudo-elements. Sure, it’s a constraint we put on ourselves, but it also pushed us to explore CSS and try to find innovative solutions to common use cases. So, before pumping extra markup into your HTML, think about whether CSS is already capable of handling the task.

You can find more fancy effects for images on my CSS Tip website. Here are a few examples:

Fancy Image Decorations series


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Fancy Image Decorations: Masks and Advanced Hover Effects https://css-tricks.com/fancy-image-decorations-masks-and-advanced-hover-effects/ https://css-tricks.com/fancy-image-decorations-masks-and-advanced-hover-effects/#comments Fri, 21 Oct 2022 12:46:27 +0000 https://css-tricks.com/?p=374194 Welcome to Part 2 of this three-part series! We are still decorating images without any extra elements and pseudo-elements. I hope you already took the time to digest Part 1 because we will continue working with a lot of gradients …


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Welcome to Part 2 of this three-part series! We are still decorating images without any extra elements and pseudo-elements. I hope you already took the time to digest Part 1 because we will continue working with a lot of gradients to create awesome visual effects. We are also going to introduce the CSS mask property for more complex decorations and hover effects.

Fancy Image Decorations series

Let’s turn to the first example we’re working on together…

The Postage Stamp

Believe or not, all it takes to make postage stamp CSS effect is two gradients and a filter:

img {
  --r: 10px; /* control the radius of the circles */
  padding: calc(2 * var(--r));
  filter: grayscale(.4);
  background: 
    radial-gradient(var(--r),#0000 98%,#fff) round
      calc(-1.5 * var(--r)) calc(-1.5 * var(--r)) / calc(3 * var(--r)) calc(3 * var(--r)),
    linear-gradient(#fff 0 0) no-repeat
      50% / calc(100% - 3 * var(--r)) calc(100% - 3 * var(--r));
}

As we saw in the previous article, the first step is to make space around the image with padding so we can draw a background gradient and see it there. Then we use a combination of radial-gradient() and linear-gradient() to cut those circles around the image.

Here is a step-by-step illustration that shows how the gradients are configured:

Note the use of the round value in the second step. It’s very important for the trick as it ensures the size of the gradient is adjusted to be perfectly aligned on all the sides, no matter what the image width or height is.

From the specification: The image is repeated as often as will fit within the background positioning area. If it doesn’t fit a whole number of times, it is rescaled so that it does.

The Rounded Frame

Let’s look at another image decoration that uses circles…

This example also uses a radial-gradient(), but this time I have created circles around the image instead of the cut-out effect. Notice that I am also using the round value again. The trickiest part here is the transparent gap between the frame and the image, which is where I reach for the CSS mask property:

img {
  --s: 20px; /* size of the frame */
  --g: 10px; /* the gap */
  --c: #FA6900; 

  padding: calc(var(--g) + var(--s));
  background: 
    radial-gradient(farthest-side, var(--c) 97%, #0000) 
      0 0 / calc(2 * var(--s)) calc(2 * var(--s)) round;
  mask:
    conic-gradient(from 90deg at calc(2 * var(--s)) calc(2 * var(--s)), #0000 25%, #000 0)
      calc(-1 * var(--s)) calc(-1 * var(--s)),
    linear-gradient(#000 0 0) content-box;
}

Masking allows us to show the area of the image — thanks to the linear-gradient() in there — as well as 20px around each side of it — thanks to the conic-gradient(). The 20px is nothing but the variable --s that defines the size of the frame. In other words, we need to hide the gap.

Here’s what I mean:

The linear gradient is the blue part of the background while the conic gradient is the red part of the background. That transparent part between both gradients is what we cut from our element to create the illusion of an inner transparent border.

The Inner Transparent Border

For this one, we are not going to create a frame but rather try something different. We are going to create a transparent inner border inside our image. Probably not that useful in a real-world scenario, but it’s good practice with CSS masks.

Similar to the previous example, we are going to rely on two gradients: a linear-gradient() for the inner part, and a conic-gradient() for the outer part. We’ll leave a space between them to create the transparent border effect.

img {
  --b: 5px;  /* the border thickness */
  --d: 20px; /* the distance from the edge */

  --_g: calc(100% - 2 * (var(--d) + var(--b)));
  mask:
    conic-gradient(from 90deg at var(--d) var(--d), #0000 25%, #000 0)
      0 0 / calc(100% - var(--d)) calc(100% - var(--d)),
    linear-gradient(#000 0 0) 50% / var(--_g) var(--_g) no-repeat;
}
Detailing the parts of the image that correspond to CSS variables.

You may have noticed that the conic gradient of this example has a different syntax from the previous example. Both are supposed to create the same shape, so why are they different? It’s because we can reach the same result using different syntaxes. This may look confusing at first, but it’s a good feature. You are not obliged to find the solution to achieve a particular shape. You only need to find one solution that works for you out of the many possibilities out there.

Here are four ways to create the outer square using gradients:

There are even more ways to pull this off, but you get the point.

There is no Best™ approach. Personally, I try to find the one with the smallest and most optimized code. For me, any solution that requires fewer gradients, fewer calculations, and fewer repeated values is the most suitable. Sometimes I choose a more verbose syntax because it gives me more flexibility to change variables and modify things. It comes with experience and practice. The more you play with gradients, the more you know what syntax to use and when.

Let’s get back to our inner transparent border and dig into the hover effect. In case you didn’t notice, there is a cool hover effect that moves that transparent border using a font-size trick. The idea is to define the --d variable with a value of 1em. This variables controls the distance of the border from the edge. We can transform like this:

--_d: calc(var(--d) + var(--s) * 1em)

…giving us the following updated CSS:

img {
  --b: 5px;  /* the border thickness */
  --d: 20px; /* the distance from the edge */
  --o: 15px; /* the offset on hover */
  --s: 1;    /* the direction of the hover effect (+1 or -1)*/

  --_d: calc(var(--d) + var(--s) * 1em);
  --_g: calc(100% - 2 * (var(--_d) + var(--b)));
  mask:
    conic-gradient(from 90deg at var(--_d) var(--_d), #0000 25%, #000 0)
     0 0 / calc(100% - var(--_d)) calc(100% - var(--_d)),
    linear-gradient(#000 0 0) 50% / var(--_g) var(--_g) no-repeat;
  font-size: 0;
  transition: .35s;
}
img:hover {
  font-size: var(--o);
}

The font-size is initially equal to 0 ,so 1em is also equal to 0 and --_d is be equal to --d. On hover, though, the font-size is equal to a value defined by an --o variable that sets the border’s offset. This, in turn, updates the --_d variable, moving the border by the offset. Then I add another variable, --s, to control the sign that decides whether the border moves to the inside or the outside.

The font-size trick is really useful if we want to animate properties that are otherwise unanimatable. Custom properties defined with @property can solve this but support for it is still lacking at the time I’m writing this.

The Frame Reveal

We made the following reveal animation in the first part of this series:

We can take the same idea, but instead of a border with a solid color we will use a gradient like this:

If you compare both codes you will notice the following changes:

  1. I used the same gradient configuration from the first example inside the mask property. I simply moved the gradients from the background property to the mask property.
  2. I added a repeating-linear-gradient() to create the gradient border.

That’s it! I re-used most of the same code we already saw — with super small tweaks — and got another cool image decoration with a hover effect.

/* Solid color border */

img {
  --c: #8A9B0F; /* the border color */
  --b: 10px;   /* the border thickness*/
  --g: 5px;  /* the gap on hover */

  padding: calc(var(--g) + var(--b));
  --_g: #0000 25%, var(--c) 0;
  background: 
    conic-gradient(from 180deg at top var(--b) right var(--b), var(--_g))
     var(--_i, 200%) 0 / 200% var(--_i, var(--b)) no-repeat,
    conic-gradient(at bottom var(--b) left  var(--b), var(--_g))
     0 var(--_i, 200%) / var(--_i, var(--b)) 200% no-repeat;
  transition: .3s, background-position .3s .3s;
  cursor: pointer;
}
img:hover {
  --_i: 100%;
  transition: .3s, background-size .3s .3s;
}
/* Gradient color border */

img {
  --b: 10px; /* the border thickness*/
  --g: 5px;  /* the gap on hover */
  background: repeating-linear-gradient(135deg, #F8CA00 0 10px, #E97F02 0 20px, #BD1550 0 30px);

  padding: calc(var(--g) + var(--b));
  --_g: #0000 25%, #000 0;
  mask: 
    conic-gradient(from 180deg at top var(--b) right var(--b), var(--_g))
     var(--_i, 200%) 0 / 200% var(--_i, var(--b)) no-repeat,
    conic-gradient(at bottom var(--b) left  var(--b), var(--_g))
     0 var(--_i, 200%) / var(--_i, var(--b)) 200% no-repeat,
    linear-gradient(#000 0 0) content-box;
  transition: .3s, mask-position .3s .3s;
  cursor: pointer;
}
img:hover {
  --_i: 100%;
  transition: .3s, mask-size .3s .3s;
}

Let’s try another frame animation. This one is a bit tricky as it has a three-step animation:

The first step of the animation is to make the bottom edge bigger. For this, we adjust the background-size of a linear-gradient():

You are probably wondering why I am also adding the top edge. We need it for the third step. I always try to optimize the code I write, so I am using one gradient to cover both the top and bottom sides, but the top one is hidden and revealed later with a mask.

For the second step, we add a second gradient to show the left and right edges. But this time, we do it using background-position:

We can stop here as we already have a nice effect with two gradients but we are here to push the limits so let’s add a touch of mask to achieve the third step.

The trick is to make the top edge hidden until we show the bottom and the sides and then we update the mask-size (or mask-position) to show the top part. As I said previously, we can find a lot of gradient configurations to achieve the same effect.

Here is an illustration of the gradients I will be using:

I am using two conic gradients having a width equal to 200%. Both gradients cover the area leaving only the top part uncovered (that part will be invisible later). On hover, I slide both gradients to cover that part.

Here is a better illustration of one of the gradients to give you a better idea of what’s happening:

Now we put this inside the mask property and we are done! Here is the full code:

img {
  --b: 6px;  /* the border thickness*/
  --g: 10px; /* the gap */
  --c: #0E8D94;

  padding: calc(var(--b) + var(--g));
  --_l: var(--c) var(--b), #0000 0 calc(100% - var(--b)), var(--c) 0;
  background:
    linear-gradient(var(--_l)) 50%/calc(100% - var(--_i,80%)) 100% no-repeat,
    linear-gradient(90deg, var(--_l)) 50% var(--_i,-100%)/100% 200% no-repeat;  
  mask:
    conic-gradient(at 50% var(--b),#0000 25%, #000 0) calc(50% + var(--_i, 50%)) / 200%,
    conic-gradient(at 50% var(--b),#000 75%, #0000 0) calc(50% - var(--_i, 50%)) / 200%;
  transition: 
    .3s calc(.6s - var(--_t,.6s)) mask-position, 
    .3s .3s background-position,
    .3s var(--_t,.6s) background-size,
    .4s transform;
  cursor: pointer;
}
img:hover {
  --_i: 0%;
  --_t: 0s;
  transform: scale(1.2);
}

I have also introduced some variables to optimize the code, but you should be used to this right now.

What about a four-step animation? Yes, it’s possible!

No explanation for this because it’s your homework! Take all that you have learned in this article to dissect the code and try to articulate what it’s doing. The logic is similar to all the previous examples. The key is to isolate each gradient to understand each step of the animation. I kept the code un-optimized to make things a little easier to read. I do have an optimized version if you are interested, but you can also try to optimize the code yourself and compare it with my version for additional practice.

Wrapping up

That’s it for Part 2 of this three-part series on creative image decorations using only the <img> element. We now have a good handle on how gradients and masks can be combined to create awesome visual effects, and even animations — without reaching for extra elements or pseudo-elements. Yes, a single <img> tag is enough!

We have one more article in this series to go. Until then, here is a bonus demo with a cool hover effect where I use mask to assemble a broken image.

Fancy Image Decorations series


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Fancy Image Decorations: Single Element Magic https://css-tricks.com/fancy-image-decorations-single-element-magic/ https://css-tricks.com/fancy-image-decorations-single-element-magic/#comments Fri, 14 Oct 2022 15:37:28 +0000 https://css-tricks.com/?p=373965 As the title says, we are going to decorate images! There’s a bunch of other articles out there that talk about this, but what we’re covering here is quite a bit different because it’s more of a challenge. The challenge? …


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As the title says, we are going to decorate images! There’s a bunch of other articles out there that talk about this, but what we’re covering here is quite a bit different because it’s more of a challenge. The challenge? Decorate an image using only the <img> tag and nothing more.

That right, no extra markup, no divs, and no pseudo-elements. Just the one tag.

Sounds difficult, right? But by the end of this article — and the others that make up this little series — I’ll prove that CSS is powerful enough to give us great and stunning results despite the limitation of working with a single element.

Fancy Image Decorations series

Let’s start with our first example

Before digging into the code let’s enumerate the possibilities for styling an <img> without any extra elements or pseudo-elements. We can use border, box-shadow, outline, and, of course, background. It may look strange to add a background to an image because we cannot see it as it will be behind the image — but the trick is to create space around the image using padding and/or border and then draw our background inside that space.

I think you know what comes next since I talked about background, right? Yes, gradients! All the decorations we are going to make rely on a lot of gradients. If you’ve followed me for a while, I think this probably comes as no surprise to you at all. 😁

Let’s get back to our first example:

img {
  --s: 10px; /* control the size */
  padding: var(--s);
  border: calc(2 * var(--s)) solid #0000;
  outline: 1px solid #000;
  outline-offset: calc(-1 * var(--s));
  background: conic-gradient(from 90deg at 1px 1px, #0000 25%, #000 0);
}

We are defining padding and a transparent border using the variable --s to create a space around our image equal to three times that variable.

Why are we using both padding and border instead of one or the other? We can get by using only one of them but I need this combination for my gradient because, by default, the initial value of background-clip is border-box and background-origin is equal to padding-box.

Here is a step-by-step illustration to understand the logic:

Initially, we don’t have any borders on the image, so our gradient will create two segments with 1px of thickness. (I am using 3px in this specific demo so it’s easier to see.) We add a colored border and the gradient still gives us the same result inside the padding area (due to background-origin) but it repeats behind the border. If we make the color of the border transparent, we can use the repetition and we get the frame we want.

The outline in the demo has a negative offset. That creates a square shape at the top of the gradient. That’s it! We added a nice decoration to our image using one gradient and an outline. We could have used more gradients! But I always try to keep my code as simple as possible and I found that adding an outline is better that way.

Here is a gradient-only solution where I am using only padding to define the space. Still the same result but with a more complex syntax.

Let’s try another idea:

For this one, I took the previous example removed the outline, and applied a clip-path to cut the gradient on each side. The clip-path value is a bit verbose and confusing but here is an illustration to better see its points:

Side-by-side comparison of the image with and without using clip-path.

I think you get the main idea. We are going to combine backgrounds, outlines, clipping, and some masking to achieve different kinds of decorations. We are also going to consider some cool hover animations as an added bonus! What we’ve looked at so far is merely a small overview of what’s coming!

The Corner-Only Frame

This one takes four gradients. Each gradient covers one corner and, on hover, we expand them to create a full frame around the image. Let’s dissect the code for one of the gradients:

--b: 5px; /* border thickness */
background: conic-gradient(from 90deg at top var(--b) left var(--b), #0000 90deg, darkblue 0) 0 0;
background-size: 50px 50px; 
background-repeat: no-repeat;

We are going to draw a gradient with a size equal to 50px 50px and place it at the top-left corner (0 0). For the gradient’s configuration, here’s a step-by-step illustration showing how I reached that result.

We tend to think that gradients are only good for transitioning between two colors. But in reality, we can do so much more with them! They are especially useful when it comes to creating different shapes. The trick is to make sure we have hard stops between colors — like in the example above — rather than smooth transitions:

#0000 25%, darkblue 0

This is basically saying: “fill the gradient with a transparent color until 25% of the area, then fill the remaining area with darkblue.

You might be scratching your head over the 0 value. It’s a little hack to simplify the syntax. In reality, we should use this to make a hard stop between colors:

#0000 25%, darkblue 25%

That is more logical! The transparent color ends at 25% and darkblue starts exactly where the transparency ends, making a hard stop. If we replace the second one with 0, the browser will do the job for us, so it is a slightly more efficient way to go about it.

Somewhere in the specification, it says:

if a color stop or transition hint has a position that is less than the specified position of any color stop or transition hint before it in the list, set its position to be equal to the largest specified position of any color stop or transition hint before it.

0 is always smaller than any other value, so the browser will always convert it to the largest value that comes before it in the declaration. In our case, that number is 25%.

Now, we apply the same logic to all the corners and we end with the following code:

img {
  --b: 5px; /* border thickness */
  --c: #0000 90deg, darkblue 0; /* define the color here */
  padding: 10px;
  background:
    conic-gradient(from 90deg  at top    var(--b) left  var(--b), var(--c)) 0 0,
    conic-gradient(from 180deg at top    var(--b) right var(--b), var(--c)) 100% 0,
    conic-gradient(from 0deg   at bottom var(--b) left  var(--b), var(--c)) 0 100%,
    conic-gradient(from -90deg at bottom var(--b) right var(--b), var(--c)) 100% 100%;
  background-size: 50px 50px; /* adjust border length here */
  background-repeat: no-repeat;
}

I have introduced CSS variables to avoid some redundancy as all the gradients use the same color configuration.

For the hover effect, all I’m doing is increasing the size of the gradients to create the full frame:

img:hover {
  background-size: 51% 51%;
}

Yes, it’s 51% instead of 50% — that creates a small overlap and avoids possible gaps.

Let’s try another idea using the same technique:

This time we are using only two gradients, but with a more complex animation. First, we update the position of each gradient, then increase their sizes to create the full frame. I also introduced more variables for better control over the color, size, thickness, and even the gap between the image and the frame.

img {
  --b: 8px;  /* border thickness*/
  --s: 60px; /* size of the corner*/
  --g: 14px; /* the gap*/
  --c: #EDC951; 

  padding: calc(var(--b) + var(--g));
  background-image:
    conic-gradient(from  90deg at top    var(--b) left  var(--b), #0000 25%, var(--c) 0),
    conic-gradient(from -90deg at bottom var(--b) right var(--b), #0000 25%, var(--c) 0);
  background-position:
    var(--_p, 0%) var(--_p, 0%),
    calc(100% - var(--_p, 0%)) calc(100% - var(--_p, 0%));
  background-size: var(--s) var(--s);
  background-repeat: no-repeat;
  transition: 
    background-position .3s var(--_i,.3s), 
    background-size .3s calc(.3s - var(--_i, .3s));
}
img:hover {
  background-size: calc(100% - var(--g)) calc(100% - var(--g));
  --_p: calc(var(--g) / 2);
  --_i: 0s;
}

Why do the --_i and --_p variables have an underscore in their name? The underscores are part of a naming convention I use to consider “internal” variables used to optimize the code. They are nothing special but I want to make a difference between the variables we adjust to control the frame (like --b, --c, etc.) and the ones I use to make the code shorter.

The code may look confusing and not easy to grasp but I wrote a three-part series where I detail such technique. I highly recommend reading at least the first article to understand how I reached the above code.

Here is an illustration to better understand the different values:

Showing the same image of two classic cars three times to illustrate the CSS variables used in the code.

The Frame Reveal

Let’s try another type of animation where we reveal the full frame on hover:

Cool, right? And you if you look closely, you will notice that the lines disappear in the opposite direction on mouse out which makes the effect even more fancy! I used a similar effect in a previous article.

But this time, instead of covering all the element, I cover only a small portion by defining a height to get something like this:

This is the top border of our frame. We repeat the same process on each side of the image and we have our hover effect:

img {
  --b: 10px; /* the border thickness*/
  --g: 5px; /* the gap on hover */
  --c: #8A9B0F; 

  padding: calc(var(--g) + var(--b));
  --_g: no-repeat linear-gradient(var(--c) 0 0);
  background: 
    var(--_g) var(--_i, 0%) 0,
    var(--_g) 100% var(--_i, 0%),
    var(--_g) calc(100% - var(--_i, 0%)) 100%,
    var(--_g) 0 calc(100% - var(--_i, 0%));
  background-size: var(--_i, 0%) var(--b),var(--b) var(--_i, 0%);
  transition: .4s, background-position 0s;
  cursor: pointer;
}
img:hover {
  --_i: 100%;
}

As you can see, I am applying the same gradient four times and each one has a different position to cover only one side at a time.

Another one? Let’s go!

This one looks a bit tricky and it indeed does require some imagination to understand how two conic gradients are pulling off this kind of magic. Here is a demo to illustrate one of the gradients:

The pseudo-element simulates the gradient. It’s initially out of sight and, on hover, we first change its position to get the top edge of the frame. Then we increase the height to get the right edge. The gradient shape is similar to the ones we used in the last section: two segments to cover two sides.

But why did I make the gradient’s width 200%? You’d think 100% would be enough, right?

100% should be enough but I won’t be able to move the gradient like I want if I keep its width equal to 100%. That’s another little quirk related to how background-position works. I cover this in a previous article. I also posted an answer over at Stack Overflow dealing with this. I know it’s a lot of reading, but it’s really worth your time.

Now that we have explained the logic for one gradient, the second one is easy because it’s doing exactly the same thing, but covering the left and bottom edges instead. All we have to do is to swap a few values and we are done:

img {
  --c: #8A9B0F; /* the border color */
  --b: 10px; /* the border thickness*/
  --g: 5px;  /* the gap */

  padding: calc(var(--g) + var(--b));
  --_g: #0000 25%, var(--c) 0;
  background: 
    conic-gradient(from 180deg at top    var(--b) right var(--b), var(--_g))
     var(--_i, 200%) 0 / 200% var(--_i, var(--b))  no-repeat,
    conic-gradient(            at bottom var(--b) left  var(--b), var(--_g))
     0 var(--_i, 200%) / var(--_i, var(--b)) 200%  no-repeat;
  transition: .3s, background-position .3s .3s;
  cursor: pointer;
}
img:hover {
  --_i: 100%;
  transition: .3s, background-size .3s .3s;
}

As you can see, both gradients are almost identical. I am simply swapping the values of the size and position.

The Frame Rotation

This time we are not going to draw a frame around our image, but rather adjust the look of an existing one.

You are probably asking how the heck I am able to transform a straight line into an angled line. No, the magic is different than that. That’s just the illusion we get after combining simple animations for four gradients.

Let’s see how the animation for the top gradient is made:

I am simply updating the position of a repeating gradient. Nothing fancy yet! Let’s do the same for the right side:

Are you starting to see the trick? Both gradients intersect at the corner to create the illusion where the straight line is changed to an angled one. Let’s remove the outline and hide the overflow to better see it:

Now, we add two more gradients to cover the remaining edges and we are done:

img {
  --g: 4px; /* the gap */
  --b: 12px; /* border thickness*/
  --c: #669706; /* the color */

  padding: calc(var(--g) + var(--b));
  --_c: #0000 0 25%, var(--c) 0 50%;
  --_g1: repeating-linear-gradient(90deg ,var(--_c)) repeat-x;
  --_g2: repeating-linear-gradient(180deg,var(--_c)) repeat-y;
  background:
    var(--_g1) var(--_p, 25%) 0, 
    var(--_g2) 0 var(--_p, 125%),
    var(--_g1) var(--_p, 125%) 100%, 
    var(--_g2) 100% var(--_p, 25%);
  background-size: 200% var(--b), var(--b) 200%;
  transition: .3s;
}
img:hover {
  --_p: 75%;
}

If we take this code and slightly adjust it, we can get another cool animation:

Can you figure out the logic in this example? That’s your homework! The code may look scary but it uses the same logic as the previous examples we looked at. Try to isolate each gradient and imagine how it animates.

Wrapping up

That’s a lot of gradients in one article!

It sure is and I warned you! But if the challenge is to decorate an image without an extra elements and pseudo-elements, we are left with only a few possibilities and gradients are the most powerful option.

Don’t worry if you are a bit lost in some of the explanations. I always recommend some of my old articles where I go into greater detail with some of the concepts we recycled for this challenge.

I am gonna leave with one last demo to hold you over until the next article in this series. This time, I am using radial-gradient() to create another funny hover effect. I’ll let you dissect the code to grok how it works. Ask me questions in the comments if you get stuck!

Fancy Image Decorations series


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How to Create Wavy Shapes & Patterns in CSS https://css-tricks.com/how-to-create-wavy-shapes-patterns-in-css/ https://css-tricks.com/how-to-create-wavy-shapes-patterns-in-css/#comments Mon, 26 Sep 2022 13:13:30 +0000 https://css-tricks.com/?p=373403 The wave is probably one of the most difficult shapes to make in CSS. We always try to approximate it with properties like border-radius and lots of magic numbers until we get something that feels kinda close. And that’s before …


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The wave is probably one of the most difficult shapes to make in CSS. We always try to approximate it with properties like border-radius and lots of magic numbers until we get something that feels kinda close. And that’s before we even get into wavy patterns, which are more difficult.

“SVG it!” you might say, and you are probably right that it’s a better way to go. But we will see that CSS can make nice waves and the code for it doesn’t have to be all crazy. And guess what? I have an online generator to make it even more trivial!

If you play with the generator, you can see that the CSS it spits out is only two gradients and a CSS mask property — just those two things and we can make any kind of wave shape or pattern. Not to mention that we can easily control the size and the curvature of the waves while we’re at it.

Some of the values may look like “magic numbers” but there’s actually logic behind them and we will dissect the code and discover all the secrets behind creating waves.

This article is a follow-up to a previous one where I built all kinds of different zig-zag, scoped, scalloped, and yes, wavy border borders. I highly recommend checking that article as it uses the same technique we will cover here, but in greater detail.

The math behind waves

Strictly speaking, there isn’t one magic formula behind wavy shapes. Any shape with curves that go up and down can be called a wave, so we are not going to restrict ourselves to complex math. Instead, we will reproduce a wave using the basics of geometry.

Let’s start with a simple example using two circle shapes:

Two gray circles.

We have two circles with the same radius next to each other. Do you see that red line? It covers the top half of the first circle and the bottom half of the second one. Now imagine you take that line and repeat it.

A squiggly red line in the shape of waves.

We already see the wave. Now let’s fill the bottom part (or the top one) to get the following:

Red wave pattern.

Tada! We have a wavy shape, and one that we can control using one variable for the circle radii. This is one of the easiest waves we can make and it’s the one I showed off in this previous article

Let’s add a bit of complexity by taking the first illustration and moving the circles a little:

Two gray circles with two bisecting dashed lines indicating spacing.

We still have two circles with the same radii but they are no longer horizontally aligned. In this case, the red line no longer covers half the area of each circle, but a smaller area instead. This area is limited by the dashed red line. That line crosses the point where both circles meet.

Now take that line and repeat it and you get another wave, a smoother one.

A red squiggly line.
A red wave pattern.

I think you get the idea. By controlling the position and size of the circles, we can create any wave we want. We can even create variables for them, which I will call P and S, respectively.

You have probably noticed that, in the online generator, we control the wave using two inputs. They map to the above variables. S is the “Size of the wave” and P is the “curvature of the wave”.

I am defining P as P = m*S where m is the variable you adjust when updating the curvature of the wave. This allows us to always have the same curvature, even if we update S.

m can be any value between 0 and 2. 0 will give us the first particular case where both circles are aligned horizontally. 2 is a kind of maximum value. We can go bigger, but after a few tests I found that anything above 2 produces bad, flat shapes.

Let’s not forget the radius of our circle! That can also be defined using S and P like this:

R = sqrt(P² + S²)/2

When P is equal to 0, we will have R = S/2.

We have everything to start converting all of this into gradients in CSS!

Creating gradients

Our waves use circles, and when talking about circles we talk about radial gradients. And since two circles define our wave, we will logically be using two radial gradients.

We will start with the particular case where P is equal to 0. Here is the illustration of the first gradient:

This gradient creates the first curvature while filling in the entire bottom area —the “water” of the wave so to speak.

.wave {
  --size: 50px;

  mask: radial-gradient(var(--size) at 50% 0%, #0000 99%, red 101%) 
    50% var(--size)/calc(4 * var(--size)) 100% repeat-x;
}

The --size variable defines the radius and the size of the radial gradient. If we compare it with the S variable, then it’s equal to S/2.

Now let’s add the second gradient:

The second gradient is nothing but a circle to complete our wave:

radial-gradient(var(--size) at 50% var(--size), blue 99%, #0000 101%) 
  calc(50% - 2*var(--size)) 0/calc(4 * var(--size)) 100%

If you check the previous article you will see that I am simply repeating what I already did there.

I followed both articles but the gradient configurations are not the same.

That’s because we can reach the same result using different gradient configurations. You will notice a slight difference in the alignment if you compare both configurations, but the trick is the same. This can be confusing if you are unfamiliar with gradients, but don’t worry. With some practice, you get used to them and you will find by yourself that different syntax can lead to the same result.

Here is the full code for our first wave:

.wave {
  --size: 50px;

  mask:
    radial-gradient(var(--size) at 50% var(--size),#000 99%, #0000 101%) 
      calc(50% - 2*var(--size)) 0/calc(4 * var(--size)) 100%,
    radial-gradient(var(--size) at 50% 0px, #0000 99%, #000 101%) 
      50% var(--size)/calc(4 * var(--size)) 100% repeat-x;
}

Now let’s take this code and adjust it to where we introduce a variable that makes this fully reusable for creating any wave we want. As we saw in the previous section, the main trick is to move the circles so they are no more aligned so let’s update the position of each one. We will move the first one up and the second down.

Our code will look like this:

.wave {
  --size: 50px;
  --p: 25px;

  mask:
    radial-gradient(var(--size) at 50% calc(var(--size) + var(--p)), #000 99%, #0000 101%) 
      calc(50% - 2*var(--size)) 0/calc(4 * var(--size)) 100%,
    radial-gradient(var(--size) at 50% calc(-1*var(--p)), #0000 99%, #000 101%) 
      50% var(--size) / calc(4 * var(--size)) 100% repeat-x;
}

I have introduced a new --p variable that’s used it to define the center position of each circle. The first gradient is using 50% calc(-1*var(--p)), so its center moves up while the second one is using calc(var(--size) + var(--p)) to move it down.

A demo is worth a thousand words:

The circles are neither aligned nor touch one another. We spaced them far apart without changing their radii, so we lost our wave. But we can fix things up by using the same math we used earlier to calculate the new radius. Remember that R = sqrt(P² + S²)/2. In our case, --size is equal to S/2; the same for --p which is also equal to P/2 since we are moving both circles. So, the distance between their center points is double the value of --p for this:

R = sqrt(var(--size) * var(--size) + var(--p) * var(--p))

That gives us a result of 55.9px.

Our wave is back! Let’s plug that equation into our CSS:

.wave {
  --size: 50px;
  --p: 25px;
  --R: sqrt(var(--p) * var(--p) + var(--size)*var(--size));

  mask:
    radial-gradient(var(--R) at 50% calc(var(--size) + var(--p)), #000 99%, #0000 101%) 
      calc(50% - 2*var(--size)) 0 / calc(4 * var(--size)) 100%,
    radial-gradient(var(--R) at 50% calc(-1*var(--p)), #0000 99%, #000 101%) 
      50% var(--size)/calc(4 * var(--size)) 100% repeat-x;
}

This is valid CSS code. sqrt() is part of the specification, but at the time I’m writing this, there is no browser support for it. That means we need a sprinkle of JavaScript or Sass to calculate that value until we get broader sqrt() support.

This is pretty darn cool: all it takes is two gradients to get a cool wave that you can apply to any element using the mask property. No more trial and error — all you need is to update two variables and you’re good to go!

Reversing the wave

What if we want the waves going the other direction, where we’re filling in the “sky” instead of the “water”. Believe it or not, all we have to do is to update two values:

.wave {
  --size: 50px;
  --p: 25px;
  --R: sqrt(var(--p) * var(--p) + var(--size) * var(--size));

  mask:
    radial-gradient(var(--R) at 50% calc(100% - (var(--size) + var(--p))), #000 99%, #0000 101%)
      calc(50% - 2 * var(--size)) 0/calc(4 * var(--size)) 100%,
    radial-gradient(var(--R) at 50% calc(100% + var(--p)), #0000 99%, #000 101%) 
      50% calc(100% - var(--size)) / calc(4 * var(--size)) 100% repeat-x;
}

All I did there is add an offset equal to 100%, highlighted above. Here’s the result:

We can consider a more friendly syntax using keyword values to make it even easier:

.wave {
  --size: 50px;
  --p: 25px;
  --R: sqrt(var(--p)*var(--p) + var(--size) * var(--size));

  mask:
    radial-gradient(var(--R) at left 50% bottom calc(var(--size) + var(--p)), #000 99%, #0000 101%) 
      calc(50% - 2 * var(--size)) 0/calc(4 * var(--size)) 100%,
    radial-gradient(var(--R) at left 50% bottom calc(-1 * var(--p)), #0000 99%, #000 101%) 
      left 50% bottom var(--size) / calc(4 * var(--size)) 100% repeat-x;
}

We’re using the left and bottom keywords to specify the sides and the offset. By default, the browser defaults to left and top — that’s why we use 100% to move the element to the bottom. In reality, we are moving it from the top by 100%, so it’s really the same as saying bottom. Much easier to read than math!

With this updated syntax, all we have to do is to swap bottom for top — or vice versa — to change the direction of the wave.

And if you want to get both top and bottom waves, we combine all the gradients in a single declaration:

.wave {
  --size: 50px;
  --p: 25px;
  --R: sqrt(var(--p)*var(--p) + var(--size)*var(--size));

  mask:
    /* Gradient 1 */
    radial-gradient(var(--R) at left 50% bottom calc(var(--size) + var(--p)), #000 99%, #0000 101%) 
      left calc(50% - 2*var(--size)) bottom 0 / calc(4 * var(--size)) 51% repeat-x,
    /* Gradient 2 */
    radial-gradient(var(--R) at left 50% bottom calc(-1 * var(--p)), #0000 99%, #000 101%) 
      left 50% bottom var(--size) / calc(4 * var(--size)) calc(51% - var(--size)) repeat-x,
    /* Gradient 3 */
    radial-gradient(var(--R) at left 50% top calc(var(--size) + var(--p)), #000 99%, #0000 101%) 
      left calc(50% - 2 * var(--size)) top 0 / calc(4 * var(--size)) 51% repeat-x,
    /* Gradient 4 */
    radial-gradient(var(--R) at left 50% top calc(-1 * var(--p)), #0000 99%, #000 101%) 
      left 50% top var(--size) / calc(4 * var(--size)) calc(51% - var(--size)) repeat-x;
}

If you check the code, you will see that in addition to combining all the gradients, I have also reduced their height from 100% to 51% so that they both cover half of the element. Yes, 51%. We need that little extra percent for a small overlap that avoid gaps.

What about the left and right sides?

It’s your homework! Take what we did with the top and bottom sides and try to update the values to get the right and left values. Don’t worry, it’s easy and the only thing you need to do is to swap values.

If you have trouble, you can always use the online generator to check the code and visualize the result.

Wavy lines

Earlier, we made our first wave using a red line then filled the bottom portion of the element. How about that wavy line? That’s a wave too! Even better is if we can control its thickness with a variable so we can reuse it. Let’s do it!

We are not going to start from scratch but rather take the previous code and update it. The first thing to do is to update the color stops of the gradients. Both gradients start from a transparent color to an opaque one, or vice versa. To simulate a line or border, we need to start from transparent, go to opaque, then back to transparent again:

#0000 calc(99% - var(--b)), #000 calc(101% - var(--b)) 99%, #0000 101%

I think you already guessed that the --b variable is what we’re using to control the line thickness. Let’s apply this to our gradients:

Yeah, the result is far from a wavy line. But looking closely, we can see that one gradient is correctly creating the bottom curvature. So, all we really need to do is rectify the second gradient. Instead of keeping a full circle, let’s make partial one like the other gradient.

Still far, but we have both curvatures we need! If you check the code, you will see that we have two identical gradients. The only difference is their positioning:

.wave {
  --size: 50px;
  --b: 10px;
  --p: 25px;
  --R: sqrt(var(--p)*var(--p) + var(--size)*var(--size));

  --_g: #0000 calc(99% - var(--b)), #000 calc(101% - var(--b)) 99%, #0000 101%;
  mask:
    radial-gradient(var(--R) at left 50% bottom calc(-1*var(--p)), var(--_g)) 
      calc(50% - 2*var(--size)) 0/calc(4*var(--size)) 100%,
    radial-gradient(var(--R) at left 50% top    calc(-1*var(--p)), var(--_g)) 
      50% var(--size)/calc(4*var(--size)) 100%;
}

Now we need to adjust the size and position for the final shape. We no longer need the gradient to be full-height, so we can replace 100% with this:

/* Size plus thickness */
calc(var(--size) + var(--b))

There is no mathematical logic behind this value. It only needs to be big enough for the curvature. We will see its effect on the pattern in just a bit. In the meantime, let’s also update the position to vertically center the gradients:

.wave {
  --size: 50px;
  --b: 10px;
  --p: 25px;
  --R: sqrt(var(--p)*var(--p) + var(--size)*var(--size));

  --_g: #0000 calc(99% - var(--b)), #000 calc(101% - var(--b)) 99%, #0000 101%;  
  mask:
    radial-gradient(var(--R) at left 50% bottom calc(-1*var(--p)), var(--_g)) 
      calc(50% - 2*var(--size)) 50%/calc(4 * var(--size)) calc(var(--size) + var(--b)) no-repeat,
    radial-gradient(var(--R) at left 50% top calc(-1 * var(--p)), var(--_g)) 50%
      50%/calc(4 * var(--size)) calc(var(--size) + var(--b)) no-repeat;
}

Still not quite there:

One gradient needs to move a bit down and the other a bit up. Both need to move by half of their height.

We are almost there! We need a small fix for the radius to have a perfect overlap. Both lines need to offset by half the border (--b) thickness:

We got it! A perfect wavy line that we can easily adjust by controlling a few variables:

.wave {
  --size: 50px;
  --b: 10px;
  --p: 25px;
  --R: calc(sqrt(var(--p) * var(--p) + var(--size) * var(--size)) + var(--b) / 2);

  --_g: #0000 calc(99% - var(--b)), #000 calc(101% - var(--b)) 99%, #0000 101%;
  mask:
    radial-gradient(var(--R) at left 50% bottom calc(-1 * var(--p)), var(--_g)) 
     calc(50% - 2*var(--size)) calc(50% - var(--size)/2 - var(--b)/2) / calc(4 * var(--size)) calc(var(--size) + var(--b)) repeat-x,
    radial-gradient(var(--R) at left 50% top calc(-1*var(--p)),var(--_g)) 
     50%  calc(50% + var(--size)/2 + var(--b)/2) / calc(4 * var(--size)) calc(var(--size) + var(--b)) repeat-x;
}

I know that the logic takes a bit to grasp. That’s fine and as I said, creating a wavy shape in CSS is not easy, not to mention the tricky math behind it. That’s why the online generator is a lifesaver — you can easily get the final code even if you don’t fully understand the logic behind it.

Wavy patterns

We can make a pattern from the wavy line we just created!

Oh no, the code of the pattern will be even more difficult to understand!

Not at all! We already have the code. All we need to do is to remove repeat-x from what we already have, and tada. 🎉

A nice wavy pattern. Remember the equation I said we’d revisit?

/* Size plus thickness */
calc(var(--size) + var(--b))

Well, this is what controls the distance between the lines in the pattern. We can make a variable out of it, but there’s no need for more complexity. I’m not even using a variable for that in the generator. Maybe I’ll change that later.

Here is the same pattern going in a different direction:

I am providing you with the code in that demo, but I’d for you to dissect it and understand what changes I made to make that happen.

Simplifying the code

In all the previous demos, we always define the --size and --p independently. But do you recall how I mentioned earlier that the online generator evaluates P as equal to m*S, where m controls the curvature of the wave? By defining a fixed multiplier, we can work with one particular wave and the code can become easier. This is what we will need in most cases: a specific wavy shape and a variable to control its size.

Let’s update our code and introduce the m variable:

.wave {
  --size: 50px;
  --R: calc(var(--size) * sqrt(var(--m) * var(--m) + 1));

  mask:
    radial-gradient(var(--R) at 50% calc(var(--size) * (1 + var(--m))), #000 99%, #0000 101%) 
      calc(50% - 2*var(--size)) 0/calc(4 * var(--size)) 100%,
    radial-gradient(var(--R) at 50% calc(-1 * var(--size) * var(--m)), #0000 99%, #000 101%) 
      50% var(--size) / calc(4 * var(--size)) 100% repeat-x;
  }

As you can see, we no longer need the --p variable. I replaced it with var(--m)*var(--size), and optimized some of the math accordingly. Now, If we want to work with a particular wavy shape, we can omit the --m variable and replace it with a fixed value. Let’s try .8 for example.

--size: 50px;
--R: calc(var(--size) * 1.28);

mask:
  radial-gradient(var(--R) at 50% calc(1.8 * var(--size)), #000 99%, #0000 101%) 
    calc(50% - 2*var(--size)) 0/calc(4 * var(--size)) 100%,
  radial-gradient(var(--R) at 50% calc(-.8 * var(--size)), #0000 99%, #000 101%) 
    50% var(--size) / calc(4 * var(--size)) 100% repeat-x;

See how the code is easier now? Only one variable to control your wave, plus you no more need to rely on sqrt() which has no browser support!

You can apply the same logic to all the demos we saw even for the wavy lines and the pattern. I started with a detailed mathmatical explanation and gave the generic code, but you may find yourself needing easier code in a real use case. This is what I am doing all the time. I rarely use the generic code, but I always consider a simplified version especially that, in most of the cases, I am using some known values that don’t need to be stored as variables. (Spoiler alert: I will be sharing a few examples at the end!)

Limitations to this approach

Mathematically, the code we made should give us perfect wavy shapes and patterns, but in reality, we will face some strange results. So, yes, this method has its limitations. For example, the online generator is capable of producing poor results, especially with wavy lines. Part of the issue is due to a particular combination of values where the result gets scrambled, like using a big value for the border thickness compared to the size:

For the other cases, it’s the issue related to some rounding that will results in misalignment and gaps between the waves:

That said, I still think the method we covered remains a good one because it produces smooth waves in most cases, and we can easily avoid the bad results by playing with different values until we get it perfect.

Wrapping up

I hope that after this article, you will no more to fumble around with trial and error to build a wavy shape or pattern. In addition to the online generator, you have all the math secrets behind creating any kind of wave you want!

The article ends here but now you have a powerful tool to create fancy designs that use wavy shapes. Here’s inspiration to get you started…

What about you? Use my online generator (or write the code manually if you already learned all the math by heart) and show me your creations! Let’s have a good collection in the comment section.


How to Create Wavy Shapes & Patterns in CSS originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

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How I Made a Pure CSS Puzzle Game https://css-tricks.com/how-i-made-a-pure-css-puzzle-game/ https://css-tricks.com/how-i-made-a-pure-css-puzzle-game/#comments Fri, 09 Sep 2022 13:21:29 +0000 https://css-tricks.com/?p=372952 I recently discovered the joy of creating CSS-only games. It’s always fascinating how HTML and CSS are capable of handling the logic of an entire online game, so I had to try it! Such games usually rely on the ol’ …


How I Made a Pure CSS Puzzle Game originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

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I recently discovered the joy of creating CSS-only games. It’s always fascinating how HTML and CSS are capable of handling the logic of an entire online game, so I had to try it! Such games usually rely on the ol’ Checkbox Hack where we combine the checked/unchecked state of a HTML input with the :checked pseudo-class in CSS. We can do a lot of magic with that one combination!

In fact, I challenged myself to build an entire game without Checkbox. I wasn’t sure if it would be possible, but it definitely is, and I’m going to show you how.

In addition to the puzzle game we will study in this article, I have made a collection of pure CSS games, most of them without the Checkbox Hack. (They are also available on CodePen.)

Want to play before we start?

I personally prefer playing the game in full screen mode, but you can play it below or open it up over here.

Cool right? I know, it’s not the Best Puzzle Game You Ever Saw™ but it’s also not bad at all for something that only uses CSS and a few lines of HTML. You can easily adjust the size of the grid, change the number of cells to control the difficulty level, and use whatever image you want!

We’re going to remake that demo together, then put a little extra sparkle in it at the end for some kicks.

The drag and drop functionality

While the structure of the puzzle is fairly straightforward with CSS Grid, the ability to drag and drop puzzle pieces is a bit trickier. I had to relying on a combination of transitions, hover effects, and sibling selectors to get it done.

If you hover over the empty box in that demo, the image moves inside of it and stays there even if you move the cursor out of the box. The trick is to add a big transition duration and delay — so big that the image takes lots of time to return to its initial position.

img {
  transform: translate(200%);
  transition: 999s 999s; /* very slow move on mouseout */
}
.box:hover img {
  transform: translate(0);
  transition: 0s; /* instant move on hover */
}

Specifying only the transition-delay is enough, but using big values on both the delay and the duration decreases the chance that a player ever sees the image move back. If you wait for 999s + 999s — which is approximately 30 minutes — then you will see the image move. But you won’t, right? I mean, no one’s going to take that long between turns unless they walk away from the game. So, I consider this a good trick for switching between two states.

Did you notice that hovering the image also triggers the changes? That’s because the image is part of the box element, which is not good for us. We can fix this by adding pointer-events: none to the image but we won’t be able to drag it later.

That means we have to introduce another element inside the .box:

That extra div (we’re using a class of .a) will take the same area as the image (thanks to CSS Grid and grid-area: 1 / 1) and will be the element that triggers the hover effect. And that is where the sibling selector comes into play:

.a {
  grid-area: 1 / 1;
}
img {
  grid-area: 1 / 1;
  transform: translate(200%);
  transition: 999s 999s;
}
.a:hover + img {
  transform: translate(0);
  transition: 0s;
}

Hovering on the .a element moves the image, and since it is taking up all space inside the box, it’s like we are hovering over the box instead! Hovering the image is no longer a problem!

Let’s drag and drop our image inside the box and see the result:

Did you see that? You first grab the image and move it to the box, nothing fancy. But once you release the image you trigger the hover effect that moves the image, and then we simulate a drag and drop feature. If you release the mouse outside the box, nothing happens.

Hmm, your simulation isn’t perfect because we can also hover the box and get the same effect.

True and we will rectify this. We need to disable the hover effect and allow it only if we release the image inside the box. We will play with the dimension of our .a element to make that happen.

Now, hovering the box does nothing. But if you start dragging the image, the .a element appears, and once released inside the box, we can trigger the hover effect and move the image.

Let’s dissect the code:

.a {
  width: 0%;
  transition: 0s .2s; /* add a small delay to make sure we catch the hover effect */
}
.box:active .a { /* on :active increase the width */
  width: 100%;
  transition: 0s; /* instant change */
}
img {
  transform: translate(200%);
  transition: 999s 999s;
}
.a:hover + img {
  transform: translate(0);
  transition: 0s;
}

Clicking on the image fires the :active pseudo-class that makes the .a element full-width (it is initially equal to 0). The active state will remain active until we release the image. If we release the image inside the box, the .a element goes back to width: 0, but we will trigger the hover effect before it happens and the image will fall inside the box! If you release it outside the box, nothing happens.

There is a little quirk: clicking the empty box also moves the image and breaks our feature. Currently, :active is linked to the .box element, so clicking on it or any of its children will activate it; and by doing this, we end up showing the .a element and triggering the hover effect.

We can fix that by playing with pointer-events. It allows us to disable any interaction with the .box while maintaining the interactions with the child elements.

.box {
  pointer-events: none;
}
.box * {
  pointer-events: initial;
}

Now our drag and drop feature is perfect. Unless you can find how to hack it, the only way to move the image is to drag it and drop it inside the box.

Building the puzzle grid

Putting the puzzle together is going to feel easy peasy compared to what we just did for the drag and drop feature. We are going to rely on CSS grid and background tricks to create the puzzle.

Here’s our grid, written in Pug for convenience:

- let n = 4; /* number of columns/rows */
- let image = "https://picsum.photos/id/1015/800/800";

g(style=`--i:url(${image})`)
  - for(let i = 0; i < n*n; i++)
    z
      a
      b(draggable="true") 

The code may look strange but it compiles into plain HTML:

<g style="--i: url(https://picsum.photos/id/1015/800/800)">
 <z>
   <a></a>
   <b draggable="true"></b>
 </z>
 <z>
   <a></a>
   <b draggable="true"></b>
 </z>
 <z>
   <a></a>
   <b draggable="true"></b>
 </z>
  <!-- etc. -->
</g>

I bet you’re wondering what’s up with those tags. None of these elements have any special meaning — I just find that the code is much easier to write using <z> than a bunch of <div class="z"> or whatever.

This is how I’ve mapped them out:

  • <g> is our grid container that contains N*N <z> elements.
  • <z> represents our grid items. It plays the role of the .box element we saw in the previous section.
  • <a> triggers the hover effect.
  • <b> represents a portion of our image. We apply the draggable attribute on it because it cannot be dragged by default.

Alright, let’s register our grid container on <g>. This is in Sass instead of CSS:

$n : 4; /* number of columns/rows */

g {
  --s: 300px; /* size of the puzzle */

  display: grid;
  max-width: var(--s);
  border: 1px solid;
  margin: auto;
  grid-template-columns: repeat($n, 1fr);
}

We’re actually going to make our grid children — the <z> elements — grids as well and have both <a> and <b> within the same grid area:

z {
  aspect-ratio: 1;
  display: grid;
  outline: 1px dashed;
}
a {
  grid-area: 1/1;
}
b {
  grid-area: 1/1;
}

As you can see, nothing fancy — we created a grid with a specific size. The rest of the CSS we need is for the drag and drop feature, which requires us to randomly place the pieces around the board. I’m going to turn to Sass for this, again for the convenience of being able to loop through and style all the puzzle pieces with a function:

b {
  background: var(--i) 0/var(--s) var(--s);
}

@for $i from 1 to ($n * $n + 1) {
  $r: (random(180));
  $x: (($i - 1)%$n);
  $y: floor(($i - 0.001) / $n);
  z:nth-of-type(#{$i}) b{
    background-position: ($x / ($n - 1)) * 100% ($y / ($n - 1)) * 100%;
    transform: 
      translate((($n - 1) / 2 - $x) * 100%, (($n - 1)/2 - $y) * 100%) 
      rotate($r * 1deg) 
      translate((random(100)*1% + ($n - 1) * 100%)) 
      rotate((random(20) - 10 - $r) * 1deg)
   }
}

You may have noticed that I’m using the Sass random() function. That’s how we get the randomized positions for the puzzle pieces. Remember that we will disable that position when hovering over the <a> element after dragging and dropping its corresponding <b> element inside the grid cell.

z a:hover ~ b {
  transform: translate(0);
  transition: 0s;
}

In that same loop, I am also defining the background configuration for each piece of the puzzle. All of them will logically share the same image as the background, and its size should be equal to the size of the whole grid (defined with the --s variable). Using the same background-image and some math, we update the background-position to show only a piece of the image.

That’s it! Our CSS-only puzzle game is technically done!

But we can always do better, right? I showed you how to make a grid of puzzle piece shapes in another article. Let’s take that same idea and apply it here, shall we?

Puzzle piece shapes

Here’s our new puzzle game. Same functionality but with more realistic shapes!

This is an illustration of the shapes on the grid:

If you look closely you’ll notice that we have nine different puzzle-piece shapes: the four corners, the four edges, and one for everything else.

The grid of puzzle pieces I made in the other article I referred to is a little more straightforward:

We can use the same technique that combines CSS masks and gradients to create the different shapes. In case you are unfamiliar with mask and gradients, I highly recommend checking that simplified case to better understand the technique before moving to the next part.

First, we need to use specific selectors to target each group of elements that shares the same shape. We have nine groups, so we will use eight selectors, plus a default selector that selects all of them.

z  /* 0 */

z:first-child  /* 1 */

z:nth-child(-n + 4):not(:first-child) /* 2 */

z:nth-child(5) /* 3 */

z:nth-child(5n + 1):not(:first-child):not(:nth-last-child(5)) /* 4 */

z:nth-last-child(5)  /* 5 */

z:nth-child(5n):not(:nth-child(5)):not(:last-child) /* 6 */

z:last-child /* 7 */

z:nth-last-child(-n + 4):not(:last-child) /* 8 */

Here is a figure that shows how that maps to our grid:

Now let’s tackle the shapes. Let’s focus on learning just one or two of the shapes because they all use the same technique — and that way, you have some homework to keep learning!

For the puzzle pieces in the center of the grid, 0:

mask: 
  radial-gradient(var(--r) at calc(50% - var(--r) / 2) 0, #0000 98%, #000) var(--r)  
    0 / 100% var(--r) no-repeat,
  radial-gradient(var(--r) at calc(100% - var(--r)) calc(50% - var(--r) / 2), #0000 98%, #000) 
    var(--r) 50% / 100% calc(100% - 2 * var(--r)) no-repeat,
  radial-gradient(var(--r) at var(--r) calc(50% - var(--r) / 2), #000 98%, #0000),
  radial-gradient(var(--r) at calc(50% + var(--r) / 2) calc(100% - var(--r)), #000 98%, #0000);

The code may look complex, but let’s focus on one gradient at a time to see what’s happening:

Two gradients create two circles (marked green and purple in the demo), and two other gradients create the slots that other pieces connect to (the one marked blue fills up most of the shape while the one marked red fills the top portion). A CSS variable, --r, sets the radius of the circular shapes.

The shape of the puzzle pieces in the center (marked 0 in the illustration) is the hardest to make as it uses four gradients and has four curvatures. All the others pieces juggle fewer gradients.

For example, the puzzle pieces along the top edge of the puzzle (marked 2 in the illustration) uses three gradients instead of four:

mask: 
  radial-gradient(var(--r) at calc(100% - var(--r)) calc(50% + var(--r) / 2), #0000 98%, #000) var(--r) calc(-1 * var(--r)) no-repeat,
  radial-gradient(var(--r) at var(--r) calc(50% - var(--r) / 2), #000 98%, #0000),
  radial-gradient(var(--r) at calc(50% + var(--r) / 2) calc(100% - var(--r)), #000 98%, #0000);

We removed the first (top) gradient and adjusted the values of the second gradient so that it covers the space left behind. You won’t notice a big difference in the code if you compare the two examples. It should be noted that we can find different background configurations to create the same shape. If you start playing with gradients you will for sure come up with something different than what I did. You may even write something that’s more concise — if so, share it in the comments!

In addition to creating the shapes, you will also find that I am increasing the width and/or the height of the elements like below:

height: calc(100% + var(--r));
width: calc(100% + var(--r));

The pieces of the puzzle need to overflow their grid cell to connect.

Final demo

Here is the full demo again. If you compare it with the first version you will see the same code structure to create the grid and the drag-and-drop feature, plus the code to create the shapes.

Possible enhancements

The article ends here but we could keep enhancing our puzzle with even more features! How about a a timer? Or maybe some sort of congratulations when the player finishes the puzzle?

I may consider all these features in a future version, so keep an eye on my GitHub repo.

Wrapping up

And CSS isn’t a programming language, they say. Ha!

I’m not trying to spark some #HotDrama by that. I say it because we did some really tricky logic stuff and covered a lot of CSS properties and techniques along the way. We played with CSS Grid, transitions, masking, gradients, selectors, and background properties. Not to mention the few Sass tricks we used to make our code easy to adjust.

The goal was not to build the game, but to explore CSS and discover new properties and tricks that you can use in other projects. Creating an online game in CSS is a challenge that pushes you to explore CSS features in great detail and learn how to use them. Plus, it’s just a lot of fun that we get something to play with when all is said and done.

Whether CSS is a programming language or not, doesn’t change the fact that we always learn by building and creating innovative stuff.


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CSS Grid and Custom Shapes, Part 2 https://css-tricks.com/css-grid-and-custom-shapes-part-2/ https://css-tricks.com/css-grid-and-custom-shapes-part-2/#comments Mon, 22 Aug 2022 14:08:39 +0000 https://css-tricks.com/?p=372396 Alright, so the last time we checked in, we were using CSS Grid and combining them with CSS clip-path and mask techniques to create grids with fancy shapes.

Here’s just one of the fantastic grids we made together:

CodePen…


CSS Grid and Custom Shapes, Part 2 originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

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Alright, so the last time we checked in, we were using CSS Grid and combining them with CSS clip-path and mask techniques to create grids with fancy shapes.

Here’s just one of the fantastic grids we made together:

CSS Grid and Custom Shapes series

Ready for the second round? We are still working with CSS Grid, clip-path, and mask, but by the end of this article, we’ll end up with different ways to arrange images on the grid, including some rad hover effects that make for an authentic, interactive experience to view pictures.

And guess what? We’re using the same markup that we used last time. Here’s that again:

<div class="gallery">
  <img src="..." alt="...">
  <img src="..." alt="...">
  <img src="..." alt="...">
  <img src="..." alt="...">
  <!-- as many times as we want -->
</div>

Like the previous article, we only need a container with images inside. Nothing more!

Nested Image Grid

Last time, our grids were, well, typical image grids. Other than the neat shapes we masked them with, they were pretty standard symmetrical grids as far as how we positioned the images inside.

Let’s try nesting an image in the center of the grid:

We start by setting a 2✕2 grid for four images:

.gallery {
  --s: 200px; /* controls the image size */
  --g: 10px; /* controls the gap between images */

  display: grid;
  gap: var(--g);
  grid-template-columns: repeat(2, auto);
}
.gallery > img {
  width: var(--s);
  aspect-ratio: 1;
  object-fit: cover;
}

Nothing complex yet. The next step is to cut the corner of our images to create the space for the nested image. I already have a detailed article on how to cut corners using clip-path and mask. You can also use my online generator to get the CSS for masking corners.

What we need here is to cut out the corners at an angle equal to 90deg. We can use the same conic-gradient technique from that article to do that:

.gallery > img {
   mask: conic-gradient(from var(--_a), #0000 90deg, #000 0);
}
.gallery > img:nth-child(1) { --_a: 90deg; }
.gallery > img:nth-child(2) { --_a: 180deg; }
.gallery > img:nth-child(3) { --_a: 0deg; }
.gallery > img:nth-child(4) { --_a:-90deg; }

We could use the clip-path method for cutting corners from that same article, but masking with gradients is more suitable here because we have the same configuration for all the images — all we need is a rotation (defined with the variable --_a) get the effect, so we’re masking from the inside instead of the outside edges.

Two by two grid of images with a white square stacked on top in the center.

Now we can place the nested image inside the masked space. First, let’s make sure we have a fifth image element in the HTML:

<div class="gallery">
  <img src="..." alt="...">
  <img src="..." alt="...">
  <img src="..." alt="...">
  <img src="..." alt="...">
  <img src="..." alt="...">
</div>

We are going to rely on the good ol’ absolute positioning to place it in there:

.gallery > img:nth-child(5) {
  position: absolute;
  inset: calc(50% - .5*var(--s));
  clip-path: inset(calc(var(--g) / 4));
}

The inset property allows us to place the image at the center using a single declaration. We know the size of the image (defined with the variable --s), and we know that the container’s size equals 100%. We do some math, and the distance from each edge should be equal to (100% - var(--s))/2.

Diagram of the widths needed to complete the design.

You might be wondering why we’re using clip-path at all here. We’re using it with the nested image to have a consistent gap. If we were to remove it, you would notice that we don’t have the same gap between all the images. This way, we’re cutting a little bit from the fifth image to get the proper spacing around it.

The complete code again:

.gallery {
  --s: 200px; /* controls the image size */
  --g: 10px;  /* controls the gap between images */
  
  display: grid;
  gap: var(--g);
  grid-template-columns: repeat(2, auto);
  position: relative;
}

.gallery > img {
  width: var(--s);
  aspect-ratio: 1;
  object-fit: cover;
  mask: conic-gradient(from var(--_a), #0000 90deg, #000 0);
}

.gallery > img:nth-child(1) {--_a: 90deg}
.gallery > img:nth-child(2) {--_a:180deg}
.gallery > img:nth-child(3) {--_a:  0deg}
.gallery > img:nth-child(4) {--_a:-90deg}
.gallery > img:nth-child(5) {
  position: absolute;
  inset: calc(50% - .5*var(--s));
  clip-path: inset(calc(var(--g) / 4));
}

Now, many of you might also be wondering: why all the complex stuff when we can place the last image on the top and add a border to it? That would hide the images underneath the nested image without a mask, right?

That’s true, and we will get the following:

No mask, no clip-path. Yes, the code is easy to understand, but there is a little drawback: the border color needs to be the same as the main background to make the illusion perfect. This little drawback is enough for me to make the code more complex in exchange for real transparency independent of the background. I am not saying a border approach is bad or wrong. I would recommend it in most cases where the background is known. But we are here to explore new stuff and, most important, build components that don’t depend on their environment.

Let’s try another shape this time:

This time, we made the nested image a circle instead of a square. That’s an easy task with border-radius But we need to use a circular cut-out for the other images. This time, though, we will rely on a radial-gradient() instead of a conic-gradient() to get that nice rounded look.

.gallery > img {
  mask: 
    radial-gradient(farthest-side at var(--_a),
      #0000 calc(50% + var(--g)/2), #000 calc(51% + var(--g)/2));
}
.gallery > img:nth-child(1) { --_a: calc(100% + var(--g)/2) calc(100% + var(--g)/2); }
.gallery > img:nth-child(2) { --_a: calc(0%   - var(--g)/2) calc(100% + var(--g)/2); }
.gallery > img:nth-child(3) { --_a: calc(100% + var(--g)/2) calc(0%   - var(--g)/2); }
.gallery > img:nth-child(4) { --_a: calc(0%   - var(--g)/2) calc(0%   - var(--g)/2); }

All the images use the same configuration as the previous example, but we update the center point each time.

Diagram showing the center values for each quadrant of the grid.

The above figure illustrates the center point for each circle. Still, in the actual code, you will notice that I am also accounting for the gap to ensure all the points are at the same position (the center of the grid) to get a continuous circle if we combine them.

Now that we have our layout let’s talk about the hover effect. In case you didn’t notice, a cool hover effect increases the size of the nested image and adjusts everything else accordingly. Increasing the size is a relatively easy task, but updating the gradient is more complicated since, by default, gradients cannot be animated. To overcome this, I will use a font-size hack to be able to animate the radial gradient.

If you check the code of the gradient, you can see that I am adding 1em:

mask: 
    radial-gradient(farthest-side at var(--_a),
      #0000 calc(50% + var(--g)/2 + 1em), #000 calc(51% + var(--g)/2 + 1em));

It’s known that em units are relative to the parent element’s font-size, so changing the font-size of the .gallery will also change the computed em value — this is the trick we are using. We are animating the font-size from a value of 0 to a given value and, as a result, the gradient is animated, making the cut-out part larger, following the size of the nested image that is getting bigger.

Here is the code that highlights the parts involved in the hover effect:

.gallery {
  --s: 200px; /* controls the image size */
  --g: 10px; /* controls the gaps between images */

  font-size: 0; /* initially we have 1em = 0 */
  transition: .5s;
}
/* we increase the cut-out by 1em */
.gallery > img {
  mask: 
    radial-gradient(farthest-side at var(--_a),
      #0000 calc(50% + var(--g)/2 + 1em), #000 calc(51% + var(--g)/2 + 1em));
}
/* we increase the size by 2em */
.gallery > img:nth-child(5) {
  width: calc(var(--s) + 2em);
}
/* on hover 1em = S/5 */
.gallery:hover {
  font-size: calc(var(--s) / 5);
}

The font-size trick is helpful if we want to animate gradients or other properties that cannot be animated. Custom properties defined with @property can solve such a problem, but support for it is still lacking at the time of writing.

I discovered the font-size trick from @SelenIT2 while trying to solve a challenge on Twitter.

Another shape? Let’s go!

This time we clipped the nested image into the shape of a rhombus. I’ll let you dissect the code as an exercise to figure out how we got here. You will notice that the structure is the same as in our examples. The only differences are how we’re using the gradient to create the shape. Dig in and learn!

Circular Image Grid

We can combine what we’ve learned here and in previous articles to make an even more exciting image grid. This time, let’s make all the images in our grid circular and, on hover, expand an image to reveal the entire thing as it covers the rest of the photos.

The HTML and CSS structure of the grid is nothing new from before, so let’s skip that part and focus instead on the circular shape and hover effect we want.

We are going to use clip-path and its circle() function to — you guessed it! — cut a circle out of the images.

Showing the two states of an image, the natural state on the left, and the hovered state on the right, including the clip-path values to create them.

That figure illustrates the clip-path used for the first image. The left side shows the image’s initial state, while the right shows the hovered state. You can use this online tool to play and visualize the clip-path values.

For the other images, we can update the center of the circle (70% 70%) to get the following code:

.gallery > img:hover {
  --_c: 50%; /* same as "50% at 50% 50%" */
}
.gallery > img:nth-child(1) {
  clip-path: circle(var(--_c, 55% at 70% 70%));
}
.gallery > img:nth-child(2) {
  clip-path: circle(var(--_c, 55% at 30% 70%));
}
.gallery > img:nth-child(3) {
  clip-path: circle(var(--_c, 55% at 70% 30%));
}
.gallery > img:nth-child(4) {
  clip-path: circle(var(--_c, 55% at 30% 30%));
}

Note how we are defining the clip-path values as a fallback inside var(). This way allows us to more easily update the value on hover by setting the value of the --_c variable. When using circle(), the default position of the center point is 50% 50%, so we get to omit that for more concise code. That’s why you see that we are only setting 50% instead of 50% at 50% 50%.

Then we increase the size of our image on hover to the overall size of the grid so we can cover the other images. We also ensure the z-index has a higher value on the hovered image, so it is the top one in our stacking context.

.gallery {
  --s: 200px; /* controls the image size */
  --g: 8px;   /* controls the gap between images */

  display: grid;
  grid: auto-flow var(--s) / repeat(2, var(--s));
  gap: var(--g);
}

.gallery > img {
  width: 100%; 
  aspect-ratio: 1;
  cursor: pointer;
  z-index: 0;
  transition: .25s, z-index 0s .25s;
}
.gallery > img:hover {
  --_c: 50%; /* change the center point on hover */
  width: calc(200% + var(--g));
  z-index: 1;
  transition: .4s, z-index 0s;
}

.gallery > img:nth-child(1){
  clip-path: circle(var(--_c, 55% at 70% 70%));
  place-self: start;
}
.gallery > img:nth-child(2){
  clip-path: circle(var(--_c, 55% at 30% 70%));
  place-self: start end;
}
.gallery > img:nth-child(3){
  clip-path: circle(var(--_c, 55% at 70% 30%));
  place-self: end start;
}
.gallery > img:nth-child(4){
  clip-path: circle(var(--_c, 55% at 30% 30%));
  place-self: end;
}

What’s going on with the place-self property? Why do we need it and why does each image have a specific value?

Do you remember the issue we had in the previous article when creating the grid of puzzle pieces? We increased the size of the images to create an overflow, but the overflow of some images was incorrect. We fixed them using the place-self property.

Same issue here. We are increasing the size of the images so each one overflows its grid cells. But if we do nothing, all of them will overflow on the right and bottom sides of the grid. What we need is:

  1. the first image to overflow the bottom-right edge (the default behavior),
  2. the second image to overflow the bottom-left edge,
  3. the third image to overflow the top-right edge, and
  4. the fourth image to overflow the top-left edge.

To get that, we need to place each image correctly using the place-self property.

Diagram showing the place-self property values for each quadrant of the grid.

In case you are not familiar with place-self, it’s the shorthand for justify-self and align-self to place the element horizontally and vertically. When it takes one value, both alignments use that same value.

Expanding Image Panels

In a previous article, I created a cool zoom effect that applies to a grid of images where we can control everything: number of rows, number of columns, sizes, scale factor, etc.

A particular case was the classic expanding panels, where we only have one row and a full-width container.

We will take this example and combine it with shapes!

Before we continue, I highly recommend reading my other article to understand how the tricks we’re about to cover work. Check that out, and we’ll continue here to focus on creating the panel shapes.

First, let’s start by simplifying the code and removing some variables

We only need one row and the number of columns should adjust based on the number of images. That means we no longer need variables for the number of rows (--n) and columns (--m ) but we need to use grid-auto-flow: column, allowing the grid to auto-generate columns as we add new images. We will consider a fixed height for our container; by default, it will be full-width.

Let’s clip the images into a slanted shape:

A headshot of a calm red wolf looking downward with vertices overlayed showing the clip-path property points.
clip-path: polygon(S 0%, 100% 0%, (100% - S) 100%, 0% 100%);

Once again, each image is contained in its grid cell, so there’s more space between the images than we’d like:

A six-panel grid of slanted images of various wild animals showing the grid lines and gaps.

We need to increase the width of the images to create an overlap. We replace min-width: 100% with min-width: calc(100% + var(--s)), where --s is a new variable that controls the shape.

Now we need to fix the first and last images, so they sort of bleed off the page without gaps. In other words, we can remove the slant from the left side of the first image and the slant from the right side of the last image. We need a new clip-path specifically for those two images.

We also need to rectify the overflow. By default, all the images will overflow on both sides, but for the first one, we need an overflow on the right side while we need a left overflow for the last image.

.gallery > img:first-child {
  min-width: calc(100% + var(--s)/2);
  place-self: start;
  clip-path: polygon(0 0,100% 0,calc(100% - var(--s)) 100%,0 100%);
}
.gallery > img:last-child {
  min-width: calc(100% + var(--s)/2);
  place-self: end;
  clip-path: polygon(var(--s) 0,100% 0,100% 100%,0 100%);
}

The final result is a nice expanding panel of slanted images!

We can add as many images as you want, and the grid will adjust automatically. Plus, we only need to control one value to control the shape!

We could have made this same layout with flexbox since we are dealing with a single row of elements. Here is my implementation.

Sure, slanted images are cool, but what about a zig-zag pattern? I already teased this one at the end of the last article.

All I’m doing here is replacing clip-path with mask… and guess what? I already have a detailed article on creating that zig-zag shape — not to mention an online generator to get the code. See how all everything comes together?

The trickiest part here is to make sure the zig-zags are perfectly aligned, and for this, we need to add an offset for every :nth-child(odd) image element.

.gallery > img {
  mask: 
    conic-gradient(from -135deg at right, #0000, #000 1deg 89deg, #0000 90deg) 
      100% calc(50% + var(--_p, 0%))/51% calc(2*var(--s)) repeat-y,
    conic-gradient(from   45deg at left,  #0000, #000 1deg 89deg, #0000 90deg) 
      0%   calc(50% + var(--_p, 0%))/51% calc(2*var(--s)) repeat-y;
}
/* we add an offset to the odd elements */
.gallery > img:nth-child(odd) {
  --_p: var(--s);
}
.gallery > img:first-child {
  mask: 
    conic-gradient(from -135deg at right, #0000, #000 1deg 89deg, #0000 90deg) 
      0 calc(50% + var(--_p, 0%))/100% calc(2*var(--s));
}
.gallery > img:last-child {
  mask: 
    conic-gradient(from 45deg at left, #0000, #000 1deg 89deg, #0000 90deg) 
      0 calc(50% + var(--_p, 0%)) /100% calc(2*var(--s));
}

Note the use of the --_p variable, which will fall back to 0% but will be equal to --_s for the odd images.

Here is a demo that illustrates the issue. Hover to see how the offset — defined by --_p — is fixing the alignment.

Also, notice how we use a different mask for the first and last image as we did in the previous example. We only need a zig-zag on the right side of the first image and the left side of the last image.

And why not rounded sides? Let’s do it!

I know that the code may look scary and tough to understand, but all that’s going on is a combination of different tricks we’ve covered in this and other articles I’ve already shared. In this case, I use the same code structure as the zig-zag and the slanted shapes. Compare it with those examples, and you will find no difference! Those are the same tricks in my previous article about the zoom effect. Then, I am using my other writing and my online generator to get the code for the mask that creates those rounded shapes.

If you recall what we did for the zig-zag, we had used the same mask for all the images but then had to add an offset to the odd images to create a perfect overlap. In this case, we need a different mask for the odd-numbered images.

The first mask:

mask: 
  linear-gradient(-90deg,#0000 calc(2*var(--s)),#000 0) var(--s),
  radial-gradient(var(--s),#000 98%,#0000) 50% / calc(2*var(--s)) calc(1.8*var(--s)) space repeat;

The second one:

mask:
  radial-gradient(calc(var(--s) + var(--g)) at calc(var(--s) + var(--g)) 50%,#0000 98% ,#000) 
  calc(50% - var(--s) - var(--g)) / 100% calc(1.8*var(--s))

The only effort I did here is update the second mask to include the gap variable (--g) to create that space between the images.

The final touch is to fix the first and last image. Like all the previous examples, the first image needs a straight left edge while the last one needs a straight right edge.

For the first image, we always know the mask it needs to have, which is the following:

.gallery > img:first-child {
  mask: 
    radial-gradient(calc(var(--s) + var(--g)) at right, #0000 98%, #000) 50% / 100% calc(1.8 * var(--s));
}
A brown bear headshot with a wavy pattern for the right border.

For the last image, it depends on the number of elements, so it matters if that element is :nth-child(odd) or :nth-child(even).

The complete grid of wild animal photos with all of the correct borders and gaps between images.
.gallery > img:last-child:nth-child(even) {
  mask: 
    linear-gradient(to right,#0000 var(--s),#000 0),
    radial-gradient(var(--s),#000 98%,#0000) left / calc(2*var(--s)) calc(1.8*var(--s)) repeat-y
}
A single-row grid of three wild animal photos with wavy borders where the last image is an odd-numbered element.
.gallery > img:last-child:nth-child(odd) {
  mask: 
    radial-gradient(calc(var(--s) + var(--g)) at left,#0000 98%,#000) 50% / 100% calc(1.8*var(--s))
}

That’s all! Three different layouts but the same CSS tricks each time:

  • the code structure to create the zoom effect
  • a mask or clip-path to create the shapes
  • a separate configuration for the odd elements in some cases to make sure we have a perfect overlap
  • a specific configuration for the first and last image to keep the shape on only one side.

And here is a big demo with all of them together. All you need is to add a class to activate the layout you want to see.

And here is the one with the Flexbox implementation

Wrapping up

Oof, we are done! I know there are many CSS tricks and examples between this article and the last one, not to mention all of the other tricks I’ve referenced here from other articles I’ve written. It took me time to put everything together, and you don’t have to understand everything at once. One reading will give you a good overview of all the layouts, but you may need to read the article more than once and focus on each example to grasp all the tricks.

Did you notice that we didn’t touch the HTML at all other than perhaps the number of images in the markup? All the layouts we made share the same HTML code, which is nothing but a list of images.

Before I end, I will leave you with one last example. It’s a “versus” between two anime characters with a cool hover effect.

What about you? Can you create something based on what you have learned? It doesn’t need to be complex — imagine something cool or funny like I did with that anime matchup. It can be a good exercise for you, and we may end with an excellent collection in the comment section.


CSS Grid and Custom Shapes, Part 2 originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

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CSS Grid and Custom Shapes, Part 1 https://css-tricks.com/css-grid-and-custom-shapes-part-1/ https://css-tricks.com/css-grid-and-custom-shapes-part-1/#comments Mon, 15 Aug 2022 13:13:47 +0000 https://css-tricks.com/?p=367324 In a previous article, I looked at CSS Grid’s ability to create complex layouts using its auto-placement powers. I took that one step further in another article that added a zooming hover effect to images in a grid layout


CSS Grid and Custom Shapes, Part 1 originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>
In a previous article, I looked at CSS Grid’s ability to create complex layouts using its auto-placement powers. I took that one step further in another article that added a zooming hover effect to images in a grid layout. This time, I want to dive into another type of grid, one that works with shapes.

Like, what if the images aren’t perfectly square but instead are shaped like hexagons or rhombuses? Spoiler alert: we can do it. In fact, we’re going to combine CSS Grid techniques we’ve looked at and drop in some CSS clip-path and mask magic to create fancy grids of images for just about any shape you can imagine!

CSS Grid and Custom Shapes series

Let’s start with some markup

Most of the layouts we are going to look at may look easy to achieve at first glance, but the challenging part is to achieve them with the same HTML markup. We can use a lot of wrappers, divs, and whatnot, but the goal of this post is to use the same and smallest amount of HTML code and still get all the different grids we want. After all, what’s CSS but a way to separate styling and markup? Our styling should not depend on the markup, and vice versa.

This said, let’s start with this:

<div class="gallery">
  <img src="..." alt="...">
  <img src="..." alt="...">
  <img src="..." alt="...">
  <img src="..." alt="...">
  <!-- as many times as we want -->
</div>

A container with images is all that we need here. Nothing more!

CSS Grid of Hexagons

This is also sometimes referred to as a “honeycomb” grid.

There are already plenty of other blog posts out there that show how to make this. Heck, I wrote one here on CSS-Tricks! That article is still good and goes way deep on making a responsive layout. But for this specific case, we are going to rely on a much simpler CSS approach.

First, let’s use clip-path on the images to create the hexagon shape and we place all of them in the same grid area so they overlap.

.gallery {
  --s: 150px; /* controls the size */
  display: grid;
}

.gallery > img {
  grid-area: 1/1;
  width: var(--s);
  aspect-ratio: 1.15;
  object-fit: cover;
  clip-path: polygon(25% 0%, 75% 0%, 100% 50%, 75% 100%, 25% 100%, 0 50%);
}
clip-path: polygon(25% 0%, 75% 0%, 100% 50%, 75% 100%, 25% 100%, 0 50%)

Nothing fancy yet. All the images are hexagons and above each other. So it looks like all we have is a single hexagon-shaped image element, but there are really seven.

The next step is to apply a translation to the images to correctly place them on the grid.

Notice that we still want one of the images to remain in the center. The rest are placed around it using CSS translate and good ol’ fashioned geometry. Here’s are the mock formulas I came up with for each image in the grid:

translate((height + gap)*sin(0deg), (height + gap)*cos(0))
translate((height + gap)*sin(60deg), (height + gap)*cos(60deg))
translate((height + gap)*sin(120deg), (height + gap)*cos(120deg))
translate((height + gap)*sin(180deg), (height + gap)*cos(180deg))
translate((height + gap)*sin(240deg), (height + gap)*cos(240deg))
translate((height + gap)*sin(300deg), (height + gap)*cos(300deg))

A few calculations and optimization later (let’s skip that boring part, right?) we get the following CSS:

.gallery {
  --s: 150px; /* control the size */
  --g: 10px;  /* control the gap */
  display: grid;
}
.gallery > img {
  grid-area: 1/1;
  width: var(--s);
  aspect-ratio: 1.15;
  object-fit: cover;
  clip-path: polygon(25% 0%, 75% 0%, 100% 50% ,75% 100%, 25% 100%, 0 50%);
  transform: translate(var(--_x,0), var(--_y,0));
}
.gallery > img:nth-child(1) { --_y: calc(-100% - var(--g)); }
.gallery > img:nth-child(7) { --_y: calc( 100% + var(--g)); }
.gallery > img:nth-child(3),
.gallery > img:nth-child(5) { --_x: calc(-75% - .87*var(--g)); }
.gallery > img:nth-child(4),
.gallery > img:nth-child(6) { --_x: calc( 75% + .87*var(--g)); }
.gallery > img:nth-child(3),
.gallery > img:nth-child(4) { --_y: calc(-50% - .5*var(--g)); }
.gallery > img:nth-child(5), 
.gallery > img:nth-child(6) { --_y: calc( 50% + .5*var(--g)); }

Maybe that’ll be easier when we get real trigonometry functions in CSS!

Each image is translated by the --_x and --_y variables that are based on those formulas. Only the second image (nth-child(2)) is undefined in any selector because it’s the one in the center. It can be any image if you decide to use a different order. Here’s the order I’m using:

With only a few lines of code, we get a cool grid of images. To this, I added a little hover effect to the images to make things fancier.

Guess what? We can get another hexagon grid by simply updating a few values.

If you check the code and compare it with the previous one you will notice that I have simply swapped the values inside clip-path and I switched between --x and --y. That’s all!

CSS Grid of Rhombuses

Rhombus is such a fancy word for a square that’s rotated 45 degrees.

Same HTML, remember? We first start by defining a 2×2 grid of images in CSS:

.gallery {
  --s: 150px; /* controls the size */

  display: grid;
  gap: 10px;
  grid: auto-flow var(--s) / repeat(2, var(--s));
  place-items: center;
}
.gallery > img {
  width: 100%; 
  aspect-ratio: 1;
  object-fit: cover;
}

The first thing that might catch your eye is the grid property. It’s pretty uncommonly used but is super helpful in that it’s a shorthand that lets you define a complete grid in one declaration. It’s not the most intuitive — and not to mention readable — property, but we are here to learn and discover new things, so let’s use it rather than writing out all of the individual grid properties.

grid: auto-flow var(--s) / repeat(2,var(--s));

/* is equivalent to this: */
grid-template-columns: repeat(2, var(--s));
grid-auto-rows: var(--s);

This defines two columns equal to the --s variable and sets the height of all the rows to --s as well. Since we have four images, we will automatically get a 2×2 grid.

Here’s another way we could have written it:

grid-template-columns: repeat(2, var(--s));
grid-template-rows: repeat(2, var(--s));

…which can be reduced with the grid shorthand:

grid: repeat(2,var(--s)) / repeat(2,var(--s));

After setting the grid, we rotate it and the images with CSS transforms and we get this:

Note how I rotate them both by 45deg, but in the opposite direction.

.gallery {
  /* etc. */
  transform: rotate(45deg);
}
.gallery > img {
  /* etc. */
  transform: rotate(-45deg);
}

Rotating the images in the negative direction prevents them from getting rotated with the grid so they stay straight. Now, we apply a clip-path to clip a rhombus shape out of them.

clip-path: polygon(50% 0, 100% 50%, 50% 100%, 0 50%)

We are almost done! We need to rectify the size of the image to make them fit together. Otherwise, they’re spaced far apart to the point where it doesn’t look like a grid of images.

The image is within the boundary of the green circle, which is the inscribed circle of the grid area where the image is placed. What we want is to make the image bigger to fit inside the red circle, which is the circumscribed circle of the grid area.

Don’t worry, I won’t introduce any more boring geometry. All you need to know is that the relationship between the radius of each circle is the square root of 2 (sqrt(2)). This is the value we need to increase the size of our images to fill the area. We will use 100%*sqrt(2) = 141% and be done!

.gallery {
  --s: 150px; /* control the size */

  display: grid;
  grid: auto-flow var(--s) / repeat(2,var(--s));
  gap: 10px;
  place-items: center;
  transform: rotate(45deg);
}
.gallery > img {
  width: 141%; /* 100%*sqrt(2) = 141% */
  aspect-ratio: 1;
  object-fit: cover;
  transform: rotate(-45deg);
  clip-path: polygon(50% 0, 100% 50%, 50% 100%, 0 50%);
}

Like the hexagon grid, we can make things fancier with that nice zooming hover effect:

CSS Grid of Triangular Shapes

You probably know by now that the big trick is figuring out the clip-path to get the shapes we want. For this grid, each element has its own clip-path value whereas the last two grids worked with a consistent shape. So, this time around, it’s like we’re working with a few different triangular shapes that come together to form a rectangular grid of images.

The three images at the top
The three images at the bottom

We place them inside a 3×2 grid with the following CSS:

.gallery {
  display: grid;
  gap: 10px; 
  grid-template-columns: auto auto auto; /* 3 columns */
  place-items: center;
}
.gallery > img {
  width: 200px; /* controls the size */
  aspect-ratio: 1;
  object-fit: cover;
}
/* the clip-path values */
.gallery > img:nth-child(1) { clip-path: polygon(0 0, 50% 0, 100% 100% ,0 100%); }
.gallery > img:nth-child(2) { clip-path: polygon(0 0, 100% 0, 50% 100%); }
.gallery > img:nth-child(3) { clip-path: polygon(50% 0, 100% 0, 100% 100%, 0 100%); }
.gallery > img:nth-child(4) { clip-path: polygon(0 0, 100% 0, 50% 100%, 0 100%); }
.gallery > img:nth-child(5) { clip-path: polygon(50% 0, 100% 100%, 0% 100%); }
.gallery > img:nth-child(6) { clip-path: polygon(0 0, 100% 0 ,100% 100%, 50% 100%); } }

Here’s what we get:

The final touch is to make the width of the middle column equal 0 to get rid of the spaces between the images. The same sort of spacing problem we had with the rhombus grid, but with a different approach for the shapes we’re using:

grid-template-columns: auto 0 auto;

I had to fiddle with the clip-path values to make sure they would all appear to fit together nicely like a puzzle. The original images overlap when the middle column has zero width, but after slicing the images, the illusion is perfect:

CSS Pizza Pie Grid

Guess what? We can get another cool grid by simply adding border-radius and overflow to our grid or triangular shapes. 🎉

CSS Grid of Puzzle Pieces

This time we are going to play with the CSS mask property to make the images look like pieces of a puzzle.

If you haven’t used mask with CSS gradients, I highly recommend this other article I wrote on the topic because it’ll help with what comes next. Why gradients? Because that’s what we’re using to get the round notches in the puzzle piece shapes.

Setting up the grid should be a cinch by now, so let’s focus instead on the mask part.

As illustrated in the above demo, we need two gradients to create the final shape. One gradient creates a circle (the green part) and the other creates the right curve while filling in the top part.

--g: 6px; /* controls the gap */
--r: 42px;  /* control the circular shapes */

background: 
  radial-gradient(var(--r) at left 50% bottom var(--r), green 95%, #0000),
  radial-gradient(calc(var(--r) + var(--g)) at calc(100% + var(--g)) 50%, #0000 95%, red)
  top/100% calc(100% - var(--r)) no-repeat;

Two variables control the shape. The --g variable is nothing but the grid gap. We need to account for the gap to correctly place our circles so they overlap perfectly when the whole puzzle is assembled. The --r variable controls the size of circular parts of the puzzle shape.

Now we take the same CSS and update a few values in it to create the three other shapes:

We have the shapes, but not the overlapping edges we need to make them fit together. Each image is limited to the grid cell it’s in, so it makes sense why the shapes are sort of jumbled at the moment:

We need to create an overflow by increasing the height/width of the images. From the above figure, we have to increase the height of the first and fourth images while we increase the width of the second and third ones. You have probably already guessed that we need to increase them using the --r variable.

.gallery > img:is(:nth-child(1),:nth-child(4)) {
  width: 100%;
  height: calc(100% + var(--r));
}
.gallery > img:is(:nth-child(2),:nth-child(3)) {
  height: 100%;
  width: calc(100% + var(--r));
}

We are getting closer!

We created the overlap but, by default, our images either overlap on the right (if we increase the width) or the bottom (if we increase the height). But that’s not what we want for the second and fourth images. The fix is to use place-self: end on those two images and our full code becomes this:

Here is another example where I am using a conic gradient instead of a radial gradient. This gives us triangular puzzle pieces while keeping the same underlying HTML and CSS.

A last one! This time I am using clip-path and since it’s a property we can animate, we get a cool hover by simply updating the custom property that controls the shape.

Wrapping up

That’s all for this first part! By combining the things we’ve already learned about CSS Grid with some added clip-path and mask magic, we were able to make grid layouts featuring different kinds of shapes. And we used the same HTML markup each time! And the markup itself is nothing more than a container with a handful of image elements!

In the second part, we are going to explore more complex-looking grids with more fancy shapes and hover effects.

I’m planning to take the demo of expanding image panels we made together in this other article:

…and transform it into a zig-zag image panels! And this is only one example among the many we will discover in the next article.


CSS Grid and Custom Shapes, Part 1 originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

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Zooming Images in a Grid Layout https://css-tricks.com/zooming-images-in-a-grid-layout/ https://css-tricks.com/zooming-images-in-a-grid-layout/#comments Mon, 08 Aug 2022 12:55:49 +0000 https://css-tricks.com/?p=367204 Creating a grid of images is easy, thanks to CSS Grid. But making the grid do fancy things after the images have been placed can be tricky to pull off.

Say you want to add some fancy hover effect to …


Zooming Images in a Grid Layout originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>
Creating a grid of images is easy, thanks to CSS Grid. But making the grid do fancy things after the images have been placed can be tricky to pull off.

Say you want to add some fancy hover effect to the images where they grow and zoom beyond the rows and columns where they sit? We can do that!

Cool, right? If you check the code, you won’t find any JavaScript, complex selectors, or even magic numbers. And this is only one example among many we will explore!

Building the grid

The HTML code to create the grid is as simple as a list of images within a container. We don’t need more than that.

<div class="gallery">
  <img>
  <img>
  <img>
  <!-- etc. -->
</div>

For the CSS, we first start by setting the grid using the following:

.gallery {
  --s: 150px; /* controls the size */
  --g: 10px;  /* controls the gap */

  display: grid;
  gap: var(--g);
  width: calc(3*var(--s) + 2*var(--g)); /* 3 times the size plus 2 times the gap */
  aspect-ratio: 1;
  grid-template-columns: repeat(3, auto);
}

In short, we have two variables, one that controls the size of the images and one that sets the size of the gap between images. aspect-ratio helps keep things in proportion.

You might be wondering why we are only defining three columns but no rows. No, I didn’t forget the rows — we just don’t need to explicitly set them. CSS Grid is capable of automatically placing items on implicit rows and columns, meaning we get as many rows as needed to any number of images we throw at it. We can explicitly define the rows instead but we need to add grid-auto-flow: column to make sure the browser will create the needed columns for us.

Here is an example to illustrate both cases. The difference is that one flows in a row direction an the other in a column direction.

Check out this other article I wrote for more about the implicit grids and the auto-placement algorithm.

Now that we have our grid, it’s time to style the images:

.gallery > img {
  width: 0;
  height: 0;
  min-height: 100%;
  min-width: 100%;
  object-fit: cover;
}

The hover effect we’re making relies on this CSS. It probably looks weird to you that we’re making images that have both no width or height but have a minimum width and height of 100%. But you will see that it’s a pretty neat trick for what we are trying to achieve.

What I’m doing here is telling the browser that the images need to have 0 width and height but also need to have a minimum height equal to 100%… but 100% of what? When using percentages, the value is relative to something else. In this case, our image is placed inside a grid cell and we need to know that size to know what’s 100% is relative to.

The browser will first ignore min-height: 100% to calculate the size of the grid cells, but it will use the height: 0 in its calculation. That means our images will not contribute to the size of the grid cells… because they technically have no physical size. This will result in three equal columns and rows that are based on the size of the grid (which we defined on the .gallery’s width and aspect-ratio). The height of each grid cell is nothing but the variable --s we defined (same for the width).

Now that we have the dimensions of our grid’s cells, the browser will use it with min-height: 100% (and min-width: 100%) which will force the images to completely fill the space of each grid cell. The whole thing may look a bit confusing but the main idea is to make sure that the grid defines the size of the images rather than the other way around. I don’t want the image to define the size of the grid and you will understand why after adding the hover effect.

Creating the hover effect

What we need to do is increase the scale of the images when they’re hovered. We can do that by adjusting an image’s width and height on :hover:

.gallery {
  --f: 1.5; /* controls the scale factor */
}

.gallery img:hover{
  width:  calc(var(--s) * var(--f));
  height: calc(var(--s) * var(--f));
}

I added a new custom variable, --f, to the mix as a scale factor to control the size on hover. Notice how I’m multiplying the size variable, --s, by it to calculate the new image size.

But you said that the image size needs to be 0. What is going on? I am lost…

What I said is still true but I am making an exception for the hovered image. I am telling the browser that only one image will have a size that’s not equal to zero — so it will contribute to the dimension of the grid — while all the others remain equal to 0.

The left side shows the grid in its natural state without any hovered images, which is what the right side is showing. All the grid cells on the left side are equal in size since all the images have no physical dimensions.

On the right side, the second image in the first row is hovered, which gives it dimensions that affect the grid cell’s size. The browser will make that specific grid cell bigger on hover, which contributes to the overall size. And since the size of the whole grid is set (because we set a fixed width on the .gallery), the other grid cells will logically respond by becoming smaller in order to keep the .gallery‘s overall size in tact.

That’s our zoom effect in action! By increasing the size of only one image we affect the whole grid configuration, and we said before that the grid defines the size of the images so that each image stretches inside its grid cell to fill all the space.

To this, we add a touch of transition and use object-fit to avoid image distortion and the illusion is perfect!

I know that the logic behind the trick is not easy to grasp. Don’t worry if you don’t fully understand it. The most important is to understand the structure of the code used and how to modify it to get more variations. That’s what we will do next!

Adding more images

We created a 3×3 grid to explain the main trick, but you have probably guessed that we there’d no need to stop there. We can make the number of columns and rows variables and add as many images as we want.

.gallery {
  --n: 3; /* number of rows*/
  --m: 4; /* number of columns */
  --s: 150px; /* control the size */
  --g: 10px;  /* control the gap */
  --f: 1.5;   /* control the scale factor */

  display: grid;
  gap: var(--g);
  width:  calc(var(--m)*var(--s) + (var(--m) - 1)*var(--g));
  height: calc(var(--n)*var(--s) + (var(--n) - 1)*var(--g));
  grid-template-columns: repeat(var(--m),auto);
}

We have two new variables for the number of rows and columns. Then we simply define the width and height of our grid using them. Same for grid-template-columns which uses the --m variable. And just like before, we don’t need to explicitly define the rows since the CSS Grid’s auto-placement feature will do the job for us no matter how many image elements we’re using.

Why not different values for the width and height? We can do that:

.gallery {
  --n: 3; /* number of rows*/
  --m: 4; /* number of columns */
  --h: 120px; /* control the height */
  --w: 150px; /* control the width */
  --g: 10px;  /* control the gap */
  --f: 1.5;   /* control the scale factor */

  display: grid;
  gap: var(--g);
  width:  calc(var(--m)*var(--w) + (var(--m) - 1)*var(--g));
  height: calc(var(--n)*var(--h) + (var(--n) - 1)*var(--g));
  grid-template-columns: repeat(var(--m),auto);
}

.gallery img:hover{
  width:  calc(var(--w)*var(--f));
  height: calc(var(--h)*var(--f));
}

We replace --s with two variables, one for the width, --w, and another one for the height, --h. Then we adjust everything else accordingly.

So, we started with a grid with a fixed size and number of elements, but then we made a new set of variables to get any configuration we want. All we have to do is to add as many images as we want and adjust the CSS variables accordingly. The combinations are limitless!

What about a full-screen version? Yes, that’s also possible. All we need is to know what values we need to assign to our variables. If we want N rows of images and we want our grid to be full screen, we first need to solve for a height of 100vh:

var(--n) * var(--h) + (var(--n) - 1) * var(--g) = 100vh

Same logic for the width, but using vw instead of vh:

var(--m) * var(--w) + (var(--m) - 1) * var(--g) = 100vw

We do the math to get:

--w: (100vw - (var(--m) - 1) * var(--g)) / var(--m)
--h: (100vh - (var(--n) - 1) * var(--g)) / var(--n)

Done!

It’s the same exact HTML but with some updated variables that change the grid’s sizing and behavior.

Note that I have omitted the formula we previously set on the .gallery‘s width and height and replaced them with 100vw and 100vh, respectively. The formula will give us the same result but since we know what value we want, we can ditch all that added complexity.

We can also simplify the --h and --w by removing the gap from the equation in favor of this:

--h: calc(100vh / var(--n)); /* Viewport height divided by number of rows */
--w: calc(100vw / var(--m)); /* Viewport width divided by number of columns */

This will make the hovered image grow a bit more than the previous example, but it is no big deal since we can control the scale with the --f variable we’re using as a multiplier.

And since the variables are used in one place we can still simplify the code by removing them altogether:

It’s important to note this optimization applies only to the full-screen example and not to the examples we’ve covered. This example is a particular case where we can make the code lighter by removing some of the complex calculation work we needed in the other examples.

We actually have everything we need to create the popular pattern of expanding panels:

Let’s dig even deeper

Did you notice that our scale factor can be less than 1? We can define the size of the hovered image to be smaller than --h or --w but the image gets bigger on hover.

The initial grid cell size is equal to --w and --h, so why do a smaller values make the grid cell bigger? Shouldn’t the cell get smaller, or at least maintain its initial size? And what is the final size of the grid cell?

We need to dig deeper into how the CSS Grid algorithm calculates the size of the grid cells. And this is involves understanding CSS Grid’s default stretch alignment.

Here’s an example to understand the logic.

On the left side of the demo, I defined a two-column with auto width. We get the intuitive result: two equal columns (and two equal grid cells). But the grid I set up on the right side of the demo, where I am updating the alignment using place-content: start, appears to have nothing.

DevTools helps show us what’s really happening in both cases:

In the second grid, we have two columns, but their widths equal zero, so we get two grid cells that are collapsed at the top-left corner of the grid container. This is not a bug but the logical result of the grid’s alignment. When we size a column (or row) with auto, it means that its content dictates its size — but we have an empty div with no content to make room for.

But since stretch is the default alignment and we have enough space inside our grid, the browser will stretch both grid cells equally to cover all that area. That’s how the grid on the left winds up with two equal columns.

From the specification:

Note that certain values of justify-content and align-content can cause the tracks to be spaced apart (space-around, space-between, space-evenly) or to be resized (stretch).

Note the “to be resized” which is the key here. In the last example, I used place-content which is the shorthand for justify-content and align-content

And this is buried somewhere in the Grid Sizing algorithm specs:

This step expands tracks that have an auto max track sizing function by dividing any remaining positive, definite free space equally amongst them. If the free space is indefinite, but the grid container has a definite min-width/height, use that size to calculate the free space for this step instead.

“Equally” explains why we wind up with equal grid cells, but it applies to “the free space” which is very important.

Let’s take the previous example and add content to one of the divs:

We added a square 50px image. Here’s an illustration of how each grid in our example responds to that image:

In the first case, we can see that the first cell (in red) is bigger than the second one (in blue). In the second case, the size of the first cell changes to fit the physical size of the image while the second cell remains with no dimensions. The free space is divided equally, but the first cell has more content inside which makes it bigger.

This is the math to figure out our free space:

(grid width) - (gap) - (image width) = (free space)
200px - 5px - 50px = 145px 

Divided by two — the number of columns — we get a width of 72.5px for each column. But we add the size of the image, 50px, to the first column which leaves us with one column at 122.5px and the second one equal to 72.5px.

The same logic applies to our grid of images. All the images have a size equal to 0 (no content) while the hovered image contributes to size — even if it’s just 1px — making its grid cell bigger than the others. For this reason, the scale factor can be any value bigger than 0 even decimals between 0 and 1.

To get the final width of the grid cells, we do the same calculation to get the following:

(container width) - (sum of all gaps) - (hovered image width) = (free space)

The width of container is defined by:

var(--m)*var(--w) + (var(--m) - 1)*var(--g)

…and all the gaps are equal to:

(var(--m) - 1)*var(--g)

…and for the hovered image we have:

var(--w)*var(--f)

We can calculate all of that with our variables:

var(--m)*var(--w) - var(--w)*var(--f) = var(--w)*(var(--m) - var(--f))

The number of columns is defined by --m ,so we divide that free space equally to get:

var(--w)*(var(--m) - var(--f))/var(--m)

…which gives us the size of the non-hovered images. For hovered images, we have this:

var(--w)*(var(--m) - var(--f))/var(--m) + var(--w)*var(--f)
var(--w)*((var(--m) - var(--f))/var(--m) + var(--f))

If we want to control the final size of the hovered image, we consider the above formula to get the exact size we want. If, for example, we want the image to be twice as big:

(var(--m) - var(--f))/var(--m) + var(--f) = 2

So, the value of our scale multiplier, --f, needs to be equal to:

var(--m)/(var(--m) - 1)

For three columns we will have 3/2 = 1.5 and that’s the scale factor I used in the first demo of this article because I wanted to make the image twice as big on hover!

The same logic applies to the height calculation and in case we want to control both of them independently we will need to consider two scale factors to make sure we have a specific width and height on hover.

.gallery {
  /* same as before */
   --fw: 1.5; /* controls the scale factor for the width */
   --fh: 1.2; /* controls the scale factor for the height */

  /* same as before */
}

.gallery img:hover{
  width:  calc(var(--w)*var(--fw));
  height: calc(var(--h)*var(--fh));
}

Now, you know all the secrets to create any kind of image grid with a cool hover effect while also having control of the sizing you want using the math we just covered.

Wrapping up

In my last article, we created a complex-looking grid with a few lines of CSS that put CSS Grid’s implicit grid and auto-placement features to use. In this article, we relied on some CSS Grid sizing trickery to create a fancy grid of images that zoom on hover and cause the grid to adjust accordingly. All of this with a simplified code that is easy to adjust using CSS variables!

In the next article, we will play with shapes! We will combine CSS grid with mask and clip-path to get fancy grid of images.


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