[Webkit-unassigned] [Bug 79659] New: Optimize Canvas fill and drawImage with SourceIn, DestinationIn, SourceOut, and DestinationAtop using transparencyLayer.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=79659

           Summary: Optimize Canvas fill and drawImage with SourceIn,
                    DestinationIn, SourceOut, and DestinationAtop using
                    transparencyLayer.
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: Canvas
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: luxtella at company100.net
                CC: mdelaney at apple.com


SourceIn, DestinationIn, SourceOut, and DestinationAtop need to update an
entire canvas, and transparencyLayer can handle well if amending little.
I represented it using GraphicsContextQt that was easy to change.
The previous implementation requires new graphicsContext creation. It is better to
delegate jobs like this to each platform. Especially, the previous implementation
causes large performance hit to GPU implementation (i.e. ACCELERATED_2D_CANVAS).

If other ports implement endTransparencyLayer like Qt, fullCanvasCompositedFill and
fullCanvasCompositedDrawImage can be removed.

Following test cases cover this patch.
    fast/canvas/canvas-composite-alpha.html
    fast/canvas/canvas-composite-canvas.html
    fast/canvas/canvas-composite-fill-repaint.html
    fast/canvas/canvas-composite-image.html
    fast/canvas/canvas-composite-transformclip.html
    fast/canvas/canvas-composite.html

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