[Webkit-unassigned] [Bug 79251] New: [chromium] Improve rubber-band overhang painting under composited path

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=79251

           Summary: [chromium] Improve rubber-band overhang painting under
                    composited path
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: New Bugs
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: asvitkine at chromium.org
                CC: thakis at chromium.org, jamesr at chromium.org


Per discussion on: https://bugs.webkit.org/show_bug.cgi?id=78008

Currently, in the composited path, rubber-band overhang painting is done by having a single layer that gets conditionally enabled and its content updated whenever the overhang is visited. This is not optimal since it involves a re-upload of the whole layer every frame.

The way it's done for !CHROMIUM Mac, is that the ScrollbarTheme sets up the overhang area layer to just be a tiled pattern and the shadow layer to be some sort of magic path-based layer that are behind the content layers. We should do something similar.

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