Bug 188841 – [Web Animations] playbackRate setter does not visually update playback rate for accelerated animations

• Component: Animations
• Status: RESOLVED DUPLICATE

Animations created by the Web Animations API do not visually adjust to new playback rates set by the playbackRate setter. If you read the playbackRate value, it properly shows the last set value, but the running animation still runs at 1x (regardless the set value). Note: There is often a noticeable jump in the animation as though the value has been updated, but the rate appears unchanged visually.

Example:
https://codepen.io/danwilson/pen/ajrxLQ?editors=0011

In the example, the input text field will update the playbackRate on the change event. It currently looks for support of updatePlaybackRate (unsupported in Safari TP 63) and falls back to the playbackRate property setter.

The console.log spits out the value from the playbackRate getter after the set (and show s the expected value), but visually the animation keeps at a 1x rate.

Steps to Reproduce:
1. Set up an animation such as:

let animation = element.animate([ { transform: 'translateX(-100%)' }, { transform: 'translateX(100%)' } ], {
  duration: 1000,
  iterations: Infinity
});

2. Immediately update playbackRate to something noticeably slower or faster

animation.playbackRate = .1;


Expected Results:
Each iteration of the animation should take 10 seconds instead of the specified 1 second because the playback rate is set to 1/10.

Actual Results:
Animation keeps playing at a rate of 1x, with a total iteration length of 1 second


Build: Release 63 (Safari 12.1, WebKit 13607.1.2.1)

[Radar WebKit Bug Importer]

<rdar://problem/43606776>

[Antoine Quint]

This is specific to the animation of hardware-accelerated properties (transform and opacity). Changing the example to use margin-left works as expected.

FYI I updated the example to have both the transform (hardware accelerated) and marginLeft available.

[Antoine Quint]

*** This bug has been marked as a duplicate of bug 204717 ***

[Antoine Quint]

This will be fixed along with bug 204717.