3D Accordion Effect - UX Lab 006

I posted the following experiment as a way of demonstrating just how far the line has blurred between web based animation and OS based animation. I saw Dribbble shots (one and two) by Indian designer Pranav Pramod and was inspired to replicate the effect in CSS3.


Unfortunately nothing is ever as easy as it seems. If it was, someone else would have already posted a similar effect. The problem is that when animating something with a 3D transform with a forced perspective, there is no way to measure or mirror the actual height represented in the browser using CSS. If you animate the parent element from 0px in height to 30px, it’s a straightforward linear animation. The 3D transform, on the other hand, changes on a non-linear scale because of the perspective.

There are two solutions, neither of which are desirable.

The first involves JavaScript, which frankly I had tried to avoid. In this example, the animation is triggered by the addition of a CSS class via JavaScript - but could just as easily be bound to an :active:target CSS event. The only way to get the actual browser rendered height of the element is to get it via JavaScript with the obj.clientHeight getter. While discussion pointed to wrapping the object in a parent element and not needing JavaScript at all, this does not work in all browsers.

Instead the JavaScript method involves binding a function with requestAnimationFrame which sets the parent objects height to mirror the calculated height of the transformed object. Accurate, but if we wanted to perform calculations many times per second, why did we bother animating with CSS at all?

The other method, considerably less accurate and very fiddly, is to match the easing or timing of the two animations. It may be possible to create a custom timing function using cubic-bezier which matches the rate of easing of a 30px tall object, rotating from -90deg to 0deg, with a perspective of 400 units. But why would you? That’s shit house.

Maybe in this instance a flat out Canvas animation would have been much more sensible. You’re still performing a function every ‘x’ milliseconds, but at least the canvas itself may be hardware accelerated. Until CSS animation matures, we will most likely have to abuse the JavaScript add-ons such as the one described earlier. Or even better yet, sever the ties with HTML and CSS and - get this right - use graphical languages for what they’re intended.

Ninja Edit: Also, you can’t yet animate background gradients so the whole 3D effect on the depth of the flaps is kind of impossible for now.

Sad-face Edit: The second I posted this, someone posted pretty much the exact same thing to Hacker News in a much more polished way. Check out Paperfold CSS.

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