[Webkit-unassigned] [Bug 206280] New: Do not detect the stopped animations in Nicosia::Animation to avoid flashback

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=206280

            Bug ID: 206280
           Summary: Do not detect the stopped animations in
                    Nicosia::Animation to avoid flashback
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebKitGTK
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: Tomoki.Imai at sony.com
                CC: bugs-noreply at webkitgtk.org

Created attachment 387759

  --> https://bugs.webkit.org/attachment.cgi?id=387759&action=review

The video shows what we see on morphing-cubes.html

How to reproduce the flashback:
- Build webkitgtk with MiniBrowser
- Run minibrowser and open https://webkit.org/blog-files/3d-transforms/morphing-cubes.html
- Push "Toggle Shape" button several times. We see flashback when the toggling shape animation stops.

Confirmed revision: r254528

The flashback was caused by using the old layer transform matrix saved when the animation has been started.

The root cause is an inconsistency of animation state in Nicosia::Animation and CoordinatedGraphicsLayer.
For Nicosia::Animation, ThreadedCompositor increases MonitonicTime for animation every frame, and calls Nicosia::Animation::apply.
For CoordinatedGraphicsLayer, CSSAnimationController updates animations list and if the animation has been finished it updates CSS value.
There is a chance to use old layer state while the Nicosia::Animation stopped, but CoordinatedGraphicsLayer still obtains old CSS value and animations.

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