[Webkit-unassigned] [Bug 69091] New: Background bleed avoidance has performance drawback

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=69091

           Summary: Background bleed avoidance has performance drawback
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: hclam at google.com
                CC: simon.fraser at apple.com


To avoid background bleeding for radius border the current best approach is to create a transparent layer to paint background and border, clipping is done at the end. While this works all the time it has performance drawback and on some sites this makes scrolling very slow.

There are several bleeding avoidance approaches currently in use, each of them as drawback.
1. Shrink background by 1 device pixel.
   Only works is border width >= 2 and all borders are present and non transparent. There are a lot of restrictions in using this method.

2. Paint to transparent layer and then clip.
   Works very well but slow.

We should derive other methods that can work around the performance issue.

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