[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 #4 from arno. <arno at renevier.net>  2012-06-21 10:53:41 PST ---
(In reply to comment #3)
> Is this a measurable perf win on a specific test?

http://renevier.net/misc/webkit_89246.html

tested with GtkLauncher

getImageData goes from 275ms to 136ms when alpha is 255
             goes from 255ms to 261ms when alpha is 128
putImageData goes from 165ms to 82ms when alpha is 255
             goes from 160ms to 165ms when alpha is 128

So, we loose about 3% or 5% speed when there is transparency (may be because of the extra condition check?), but we are twice as fast when there is no transparency.

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