[Webkit-unassigned] [Bug 90375] Parallel image decoders

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=90375





--- Comment #61 from Hin-Chung Lam <hclam at google.com>  2012-08-01 19:49:37 PST ---
(In reply to comment #59)
> I would prefer not to remove the optimizations that currentFrameHasAlpha() allows. I hope we can make more, not less use of it in future.

I agree that having the information of alpha channel can allow some nice optimizations. Currently as it is now is it a blocker for having parallel (or deferred) image decoding. Particularly the implementation requires decoding an entire frame to get this information. We would like to start image decoding only during painting.

For most cases getting the alpha channel can be done differently. Many use cases of this method is to optimize texture upload or having an opaque texture. For these use cases that involve NativeImagePtr each port can get query the native image directly.

The use of it in RenderImage is the outstanding one that doesn't involve a NativeImagePtr. It seems to benefit a specific use case. According to http://trac.webkit.org/changeset/91628 it is the case of JPEG <img> with a GIF background. Maybe we should do this optimization a different to allow parallel image decoding? For example halt GIF animation in the background?

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