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The translateZ Trick

CSS filters are great

CSS filters are super cool. They can take something that looks like this…

The Firefox logo next to the CSS declaration ‘filter: blur(0)’.

…and make it look like this:

A blurred Firefox logo next to the CSS declaration ‘filter: blur(4px)’.

Love it. Effects like these are the fun part of writing CSS.

And blur() is just one of many fun filter options. The rest are listed here.

CSS filters become especially useful when you want to animate items on and off the page, or in and out of the foreground. For example, you may want to gradually blur items as they animate out. Or gradually blur the page background when a user opens a dialog or modal.

Safari woes

Unfortunately, once you start animating the CSS filter property, you’re going to notice your animation is awfully choppy in Safari.

I ran into this issue at work and thankfully found a solution. Then I heard Scott Tolinski lament on Twitter and the Syntax podcast that he’d been forced to stop using CSS filters because of this Safari rendering issue and so I decided to write this post to help Scotty. 😎

The fix

To fix the issue in Safari, take this…

.blurry {
  filter: blur(4px);
  transition: filter 0.3s ease-in-out;

…and change it to this:

.blurry {
  filter: blur(4px);
  transition: filter 0.3s ease-in-out;
  transform: translateZ(0);

That’s it. Your animations will run smoothly in Safari now.

Why does translateZ help?

The basic reason translateZ(ANY_VALUE) makes the animation run smoothly is that it tells Safari to render it with the GPU instead of the CPU.

Without translateZ (or a similar hint like translate3d), Safari will try to animate your blur() filter using the CPU, which isn’t nearly as good at rendering complicated graphics. For graphics-intensive tasks like animating a filter effect, the GPU will always do a much better job.

Help us out, Safari

Chrome and other non-Safari browsers automatically hardware-accelerate animations like this by engaging the GPU, but Safari still requires you to add extra declarations like translateZ() to get the same result.

Hopefully the Safari team will fix that soon so Scott can animate all the CSS filters he likes without needing workarounds like this one.

Until then, translateZ() is your friend.

Further reading