[Webkit-unassigned] [Bug 258967] New: ShouldPaintUsingCompositeCopy feature is not stable with respect to layouts, resizes or similar

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=258967

            Bug ID: 258967
           Summary: ShouldPaintUsingCompositeCopy feature is not stable
                    with respect to layouts, resizes or similar
           Product: WebKit
           Version: WebKit Local Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Compositing
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: kkinnunen at apple.com
                CC: simon.fraser at apple.com,
                    webkit-bug-importer at group.apple.com
        Depends on: 258964

Somehow on resizing and bringing up the print dialog, possibly just doing layout, the m_subpixelOffsetFromRenderer gets a small value such as ~0.18. This causes the optimization to be lost, because contentsBox "moves" away from the origo, even though in practice it does not.
    auto contents = contentsBox();
    if (contents.location() != LayoutPoint(0, 0))
        return false;
E.g. repro case like:
load page
canvas gets the optimization
resize
canvas does not get the optimization
reload
canvas gets the optimization


Referenced Bugs:

https://bugs.webkit.org/show_bug.cgi?id=258964
[Bug 258964] The ShouldPaintUsingCompositeCopy feature is not inspectable with layout tests
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