[Webkit-unassigned] [Bug 107547] New: [Qt] Box shadows on a transparency layer is very slow

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=107547

           Summary: [Qt] Box shadows on a transparency layer is very slow
           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: allan.jensen at digia.com


If box shadows are applied on top of a transparency layer, the result is very slow painting. An example is the page http://paste.chakra-project.org/3755/.

The issue is that the ShadowBlur layer ends up being the entire size of box element, instead of just the size of the transparency layer. This happens because the clipping set on QPainter is much larger than the area QPainter is painting to. One way to avoid it, is to set an initial clipping to the area QPainter is painting to, so that later clipping (set by intersection), can not end up larger than the layer.

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