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JavaScript-Driven Accelerated Animations

From: Ian Vollick <vollick@chromium.org>
Date: Wed, 2 Oct 2013 14:28:07 -0400
Message-ID: <CAF10CM24cCqWZ4-yfmrtiHDw6G1er4QfAJebF2LoaQhp7nCHVQ@mail.gmail.com>
To: www-style@w3.org
Hi All,

I've been informally discussing an idea that would allow JavaScript to
drive animations of certain CSS properties from a web worker thread. I've
put together a high level explainer for the idea here:

If you have a moment, please take a look and let me know what you think.

Here's a snippet from the doc:

*JavaScript-driven animations are extremely flexible and powerful, but are
subject to main thread jank (by jank, I mean unpredictable interruptions in
the rate that animations are serviced on a thread due to other, unrelated
work on that thread). And although JavaScript can run on a web worker, DOM
access and CSS property animations are not permitted. Despite their
susceptibility to main thread jank, main thread animations are widely used;
they're the only way to create common effects such as parallax,
position-sticky, image carousels, custom scroll animations, iphone-style
contact lists, and physics-based animations. In a perfect world, the main
thread would always be responsive enough to guarantee that a JavaScript
animation callback would be serviced every frame. In reality, this is
extremely hard to achieve, both for user agents and developers of large
sites composed of disparate components. The result is a lot of janky pages.*
*Why can't we update CSS properties from a worker thread? Updating CSS
properties could effect a style recalc or a layout and those operations
must happen on the main thread. That said, there are certain 'layout-free'
properties that can be modified without these side effects. These
properties include transform, opacity and scroll offset. Clearly
identifying these layout-free properties and allowing them to be animated
from any thread would provide a simple and powerful way to achieve smooth


Received on Wednesday, 2 October 2013 21:09:02 UTC

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