[Webkit-unassigned] [Bug 60750] Optimize outline rendering to avoid transparency layers

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=60750


Darin Adler <darin at apple.com> changed:

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--- Comment #5 from Darin Adler <darin at apple.com>  2011-11-04 10:13:38 PST ---
(From update of attachment 113618)
View in context: https://bugs.webkit.org/attachment.cgi?id=113618&action=review

> Source/WebCore/rendering/RenderObject.cpp:1145
> +    if (outlineStyle == SOLID && outlineColor.hasAlpha()) {

I think this code needs a why comment.

If you look at just this code, it's surprising that we have a special case just for the case where we have alpha. A good way to make that clear is to put this optimization inside the "use transparency layer" if statement. There it is easy to see that we are avoiding an expensive transparency layer. Otherwise, it is unclear why there is no fast case for the case where we don’t have alpha. The reason is that the code is already fast, and this alternate implemenation would probably be slower, in cases where we are not making a transparency layer.

So you could just add a comment, or you could even put this entire fast case inside the useTransparencyLayer if statement, or you could at least use the useTransparencyLayer boolean to trigger this fast case.

I think the key is that this is an optimization because it avoids the transparency layer and the code should make this crystal clear.

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