[Webkit-unassigned] [Bug 188841] New: Web Animations API: playbackRate setter does not visually update playback rate

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=188841

            Bug ID: 188841
           Summary: Web Animations API: playbackRate setter does not
                    visually update playback rate
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Macintosh
                OS: macOS 10.13
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Animations
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: dwilson1 at gmail.com
                CC: dino at apple.com

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)

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