CSS - Animation

FLIP.js

FLIP is an approach to animations that remaps animating expensive properties, like width, height, left and top to significantly cheaper changes using transforms. It does this by taking two snapshots, one of the element’s First position (F), another of its Last position (L). It then uses a transform to Invert (I) the element’s changes, such that the element appears to still be in the First position. Lastly it Plays (P) the animation forward by removing the transformations applied in the Invert step.

Animating with Clip-Path

clip-path is one of those CSS properties we generally know is there but might not reach for often for whatever reason. It’s a little intimidating in the sense that it feels like math class because it requires working with geometric shapes, each with different values that draw certain shapes in certain ways.

We’re going to dive right into clip-path in this article, specifically looking at how we can use it to create pretty complex animations. I hope you’ll see just how awesome the property and it’s shape-shifting powers can be.

Splitting - text animation library

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A stylized "Splitting" with a banana mascot.
That's one determined banana.

Splitting creates elements and adds CSS variables to unlock amazing possibilities for animating text, grids, and more!

DoubleDash your CSS

The previously impractical becomes easy with Splitting’s CSS Variables.

Comically Small

A shocking amount of features in a 1.5kb (minified & gzipped) package.

Progressively Enhance

Upgrade websites for modern browsers without breaking IE.

Responsive Design for Motion, a.k.a. "prefers-reduced-motion" Media Query

WebKit now supports the prefers-reduced-motion media feature, part of CSS Media Queries Level 5, User Preferences. The feature can be used in a CSS @media block or through the window.matchMedia() interface in JavaScript. Web designers and developers can use this feature to serve alternate animations that avoid motion sickness triggers experienced by some site visitors.

To explain who this media feature is for, and how it’s intended to work, we’ll cover some background. Skip directly to the code samples or prefers-reduced-motion demo if you wish.

CSS deep-dive: matrix3d() for a frame-perfect custom scrollbar

I haven’t checked how accessible this is, and I’m torn on the concept of custom scrollbars, but this is interesting at the very least:

Custom scrollbars are extremely rare and that’s mostly due to the fact that scrollbars are one of the remaining bits on the web that are pretty much unstylable (I’m looking at you, date picker). You can use JavaScript to build your own, but that’s expensive, low fidelity and can feel laggy. In this article we will leverage some unconventional CSS matrices to build a custom scroller that doesn’t require any JavaScript while scrolling, just some setup code.

TL;DR:

You don’t care about the nitty gritty? You just want to look at the Nyan cat demo and get the library? You can find the demo’s code in our GitHub repo.

Building performant expand & collapse animations

Use scale transforms when animating clips. You can prevent the children from being stretched and skewed during the animation by counter-scaling them.

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In this post we’re going to look over what’s involved if you want performant clip animations. If you want to see a demo, check out the Sample UI Elements GitHub repo.

Using CSS Transitions on Auto Dimensions

We’ve all been there. You’ve got an element you want to be able to collapse and expand smoothly using CSS transitions, but its expanded size needs to be content-dependent. You’ve set transition: height 0.2s ease-out. You’ve created a collapsed CSS class that applies height: 0. You try it out, and… the height doesn’t transition. It snaps between the two sizes as if transition had never been set. After some fiddling, you figure out that this problem only happens when the height starts out or ends up as auto. Percentages, pixel values, any absolute units work as expected. But all of those require hard coding a specific height beforehand, rather than allowing it to naturally result from the size of the element content.

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If you were hoping I had a magical, complete solution to this problem, I’m sorry to disappoint you. There’s no one solution that achieves the desired effect without downsides. There are, however, multiple workarounds that each come with a different set of advantages and disadvantages, and in most use cases at least one of them will get the job done in an acceptable manner. I’ll outline the major ones, and list out their ups and downs so you can hopefully pick the best one for your situation.

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Technique 1: max-height

If you web search this problem, the max-height approach will probably be mentioned in all of the first five to ten results. It’s actually pretty unideal, but I thought it was worth including here for the sake of comparison.

It works like this: CSS values can only be transitioned to and from fixed unit values. But imagine we have an element whose height is set to auto, but whose max-height is set to a fixed value; say, 1000px. We can’t transition height, but we can transition max-height, since it has an explicit value. At any given moment, the actual height of the element will be the maximum of the height and the max-height. So as long as max-height’s value is greater than what auto comes out to, we can just transition max-height and achieve a version of the desired effect.

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Technique 2: transform: scaleY()

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Implementation works like this: we set a transition for the element’s transform property, then toggle between transform: scaleY(1) and transform: scaleY(0). These mean, respectively, “render this element at the same scale (on the y axis) that it starts out at” and “render this element at a scale of 0 (on the y axis)”. Transitioning between these two states will neatly “squish” the element to and from its natural, content-based size.

Technique 3: JavaScript

Managing a CSS transition in CSS would be ideal, but as we’re learning, sometimes it just isn’t entirely possible.

If you absolutely have to have smoothly collapsing sections, whose expanded size is completely driven by their content, and which other elements on the page will flow around as they transition, you can achieve that with some JavaScript.

The basic strategy is to manually do what the browser refuses to: calculate the full size of the element’s contents, then CSS transition the element to that explicit pixel size.