[Webkit-unassigned] [Bug 89246] do not multiply/demultiply colors when alpha is 255

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=89246





--- Comment #15 from arno. <arno at renevier.net>  2012-08-02 10:42:21 PST ---
Actually, I discovered that skipping the calls to premultipliedARGBFromColor/colorFromPremultipliedARGB, and performing the computation inside the loop is much faster. This optimization is already performed in webkitVideoSinkRender:
http://trac.webkit.org/browser/trunk/Source/WebCore/platform/graphics/gstreamer/VideoSinkGStreamer.cpp?rev=124472#L212
This makes getImageData 10% faster, and putImageData 30% faster.

Then, if I don't perform the multiply/demultiply when alpha is 255, it's still 3%/5% slower with transparency. But with the 10%/30% previous win, overall, there is no case with performance loss.

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