Smarter toggling for good design and great performance
This is a repost of a post I’ve written for our company-blog, iAllenkelhet.
Good design isn’t just how it looks, but also how it works. This is why code is an important part of our design process at Netlife Research. By coding we can control other important design aspects of our website like speed, animation and how the design “feels”. We can also test how the site behaves on different devices and browsers.
A much used effective design pattern is toggling. Toggling lets us hide parts of the content behind a button to make the content more easily scannable. The main problem with toggling is performance. Smaller devices have the most to gain from toggling, yet ironically, they also are the least capable of rendering it. We usually have two different methods for toggling of content:
- Using jQuery's slideToggle. This is usually the best solution. The content slides in gradually and pushes the elements beneath it down. jQuery basically increases the height of the expanding element multiple times each second. On a fast desktop computer it looks like a nice animation, but on smartphones and tablets it can often become choppy and sluggish.
- Turning a hide class on and off. We can achieve the same result by adding or removing a class with the
display:noneproperty. This works well on any device, but is very sudden. The element doesn’t expand: it’s either visible or hidden. This can at times feel confusing for the user, especially if you are expanding a lot of content.
Performance of transitions
Neither of these solutions are optimal in my opinion. Even though I’m not a developer, I understand that performance is an important part of the overall user experience. I therefore looked further into how we could have a toggle-solution that animates and works well on most mobile devices. With CSS3 we have the opportunity to animate and use transitions in CSS. We can use transitions to animate the height (or max-height) of the expanded element. But it would still perform badly since we don’t make use of the devices GPU (Graphic Processing Unit) for rendering the animation and moving the content underneath. The only CSS properties that invoke the GPU to make smooth animations on mobile are transform and opacity. The optimal solution would be to move the content away with the transform property. The problem with transform is that it just moves the content from it’s original position: it still takes up the same space as it did before, leaving us stuck with a big empty area. The same is true for all the GPU invoking techniques.
[quote]The more content the browser has to rewrite, the slower it renders. [/quote]
Rewriting the content
Another important aspect of making smooth animations is that the more content the browser has to rewrite, the slower it renders. To avoid affecting other elements it’s therefore recommended that animated elements are
position:fixed;. After trying out a variety of different approaches I ended up fading the content in or out via opacity, and clever use of positioning combined with
display:none; when the animation is finished. We still manage to push all the content underneath the element down, but with only one rewrite compared to a regular slideToggle tens of times each second. This performs nicely on mobile where the content fades in, and because it’s under the fold you won’t notice that the content is getting pushed down.
Example showing how a regular slideToggle works compared to the cssToggle-plugin
I’ve made my approach available as a jQuery plugin called cssToggle. In short the plugin checks if the element it’s called on is
display:none; or not, then shows or hides the element via CSS opacity. When the animation is finished it sets the element to
display:block; based on it’s previous state. cssToggle also takes multiple options like position, speed, easing and firing functions after the animation is finished. This way you can easily tailor it to suit your needs. The plugin is about 1kb minified, and gracefully degrades on browsers that don’t support animations and just hides or shows the content with no fading. Grab the plugin on gitHub.
PS: If you would like a regular
slideToggle(); on devices that can handle it, you could also use the excellent tool Modernizr and replace all your slideToggles with cssToggle when you detect touch-devices. While you’re at it I would also enable fastclick on these elements, to get rid of the 300ms wait before a click is registered.