[Webkit-unassigned] [Bug 203112] New: A combination of scrolling and a content change can leave a fixed layer in the wrong place

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=203112

            Bug ID: 203112
           Summary: A combination of scrolling and a content change can
                    leave a fixed layer in the wrong place
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Scrolling
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: simon.fraser at apple.com

The patch in bug 196612 changes scrollingcoordinator/ios/ui-scroll-fixed.html to avoid this bug, but we should fix the underlying bug too.

The bug is that a UI scroll can cause an offset to be applied to a CALayer in the UI process, but the combination of a content change and the scroll means that the GraphicsLayerCA ends up with the same position it had before. When that layer+scrolling tree is committed, nothing fixes up the CALayer position in the UI process.

We can also leave a wrong "approximate position" on the GraphicsLayer in this situation.

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