[Webkit-unassigned] [Bug 273336] New: requestAnimationFrame glitches detected on touchstart/touchend/pointerdown/pointerup op

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=273336

            Bug ID: 273336
           Summary: requestAnimationFrame glitches detected on
                    touchstart/touchend/pointerdown/pointerup op
           Product: WebKit
           Version: Safari 17
          Hardware: iPhone / iPad
                OS: iOS 17
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: fuweichin at gmail.com

Created attachment 471167

  --> https://bugs.webkit.org/attachment.cgi?id=471167&action=review

detected animation glitches on touch tap

Steps to Reproduce:

1. Open demo https://beta.tourofdreamland.net/device-tests/screen/animation-frame-rate/ you will see a canvas rendering rAF interval bins in realtime with portion of 1px height per 1ms interval.
2. Click anywhere on page with mouse/touch/pen, then you may see glitches (or say short time stuttering) of interval bins rendered in realtime. (tip: take a screenshot before glitchy bins run out)


Expected result:

Animation frame scheduling shouldn't be affected like that, , especially when there are no busy microtasks running.


Actual result:

Animation glitches can be detected on touchstart/touchend/pointerdown/pointerup op.
No matter what rendering frame rate is, e.g. 30fps (with Low Power Mode turned on), 60fps or 120fps (with "Prefer Page Rendering Updates near 60fps" disabled).
No matter what type of stat timestamp is in use, e.g. rAF callback time or `performance.now()`, no matter cross-origin isolated is enabled or not.

BTW, pointermove op may also affect animation frame pacing, though the affection is not that obvious as pointerdown/pointerup op.


Additional Information:

Found on iPad Pro 12.9 2nd gen with iOS 17.4.1
Not on iPhone 8 Plus with iOS 16.7.7
I'm not sure if this issue is device model specific

Possiblly some other problems are related to this issue, including

1. extra delay detected on first touchmove event immediate after touchstart, reproduce with demo https://beta.tourofdreamland.net/device-tests/hid/touch-test/
2. extra delay detected on leading pointermove events immediate after pointerdown, reproduce with demo https://beta.tourofdreamland.net/device-tests/hid/pointer-motion-path-visualizer/

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