Mastering the technique

Reveal dat header

I’ll explain how the whole animation technique works by going step by step through the process of revealing the header of our sample site. We’ll start by first identifying the three agents we want to independently animate:

We basically have 3 agents that we want to reveal at different times. I have colored in blue the time offset in which each agent should reveal itself. We want Agent 1 and Agent 3 to subtly fade in from the left. For Agent 2, it makes sense to have a cool enlarge animation from left to right just as if the line was flowing from Agent 1 to Agent 3. Let’s start by defining our core CSS animations:

For fade-in-right we just define our element’s initial state as hidden and moved a bit to the left, and our final state will render our element to full opacity and will locate it back to its natural position. Look how I go with just 15px of movement range. Always avoid long-range movements; the whole secret lies in small, subtle motion. The code for grow-left is pretty much self-explanatory so I really don’t have to go into details. The cool thing here is to see I’m only animating the following two CSS properties: transform and opacity . You might want to read more about why you should avoid animating any other property if you’re truly committed to high performant, 60fps animations.

Now that we defined our animations, let’s apply them to our agents. Three important things you need to keep in mind before looking at the code:

Set the initial state of the element in its default CSS properties Use forwards as the fill mode of the animation so that it preserves its final state Orchestrate revealings via animation-delay

Look how we defined the initial state for agents 1 and 3 as opacity: 0 because we want them to be hidden until the fade-in transition comes in. Then, we set the animation to be the previously defined fade-in-right with the good old ease function and forwards fill-mode. As we still want Agent 3 to make its entrance to the scene, later on, we set an animation-delay: 0.8s which basically means that the animation won’t start up until 800 ms have passed since the element was placed on the DOM or was made visible via display property. Really easy isn’t it?

Now, for Agent 2 things are a bit different. The initial state is set to transform: scaleX(0) otherwise our element will be shown fully enlarged up until the animation kicks in. So, by setting an initial set we’re indicating how the element should render even before the animation is fired. Then we set its transform-origin: left property so that the line enlarges from left to right, otherwise, its anchor would be the center by default. We then do something similar as with agents 1 and 3 by setting animation: grow-left , its fill mode to forwards and making sure it reveals itself only after 0.4 seconds of being rendered in the DOM. The interesting bit here is the fact that we’re not using the default ease function as our animation timing function but instead we define a custom cubic-bezier function. This allows us to create more interesting and visually appealing transitions than those coming by default in the browser. Go ahead and try defining your own cubic-bezier with this pretty fun tool.

Let’s see the final result:

Pretty cool huh? Look how the animation-delay makes a lot of sense now and how agents 1 and 3 both have the same revealing motion. Coming up with the right animation durations and animation delays is a matter of tuning by trial and error so don’t stress too much about it and just have fun playing with it.

Show me the body now

It really makes no sense to go through the process of animating the rest of the content as the same technique repeats over and over again:

Identify agents and revealing timings Create appropriate animations Set initial states to agents Set animations to each agent and orchestrate via proper animation delays Tune the animation by trial and error Profit

Cool, but, you know, #perfmatters

Yeah, perf matters, and that’s why we strive to build the whole show with just transform and opacity . These are the only properties that just trigger compositing in the browser rendering process, thus avoiding computing work and therefore resulting in a jank free experience.

Let’s run a perf profiling on our revealing animation:

You go ahead and look at dat green bar. This means that 99% of the time we hit 60fps in the whole animation. 60 frames per goddamn second (sorry, I’m just so proud of that). It can’t really be more performant. Please keep in mind that the more elements you animate (known as agents in this article), the jankier your app will look like even when using the CSS golden props. This is because every animation will inevitably add a bit of GPU workload. So, try pushing to limit the number of animated elements but always strive to hit the 60fps mark.

Too much magic

“I’m really not that creative to come up with fancy animations like these”

Building great animations is not a matter of being technically competent but instead it takes quite a good sense of design and an innate drive to craft good UI interactions. This can be very difficult and only the most talented designers are creative enough to accomplish such feats. However, we mortals are still able to learn by imitating and taking as much inspiration as we can from true pros. For this I recommend you to frequently visit sites like Awwwards or Dribbble and check ideas on cool page revealing animations.