[Webkit-unassigned] [Bug 90445] Add a comment in order to clarify why BitmapImage::frameHasAlphaAtIndex returns true as default.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=90445





--- Comment #7 from Eric Seidel <eric at webkit.org>  2012-07-03 16:57:37 PST ---
(From update of attachment 150579)
View in context: https://bugs.webkit.org/attachment.cgi?id=150579&action=review

>>> Source/WebCore/platform/graphics/BitmapImage.cpp:322
>>> +    // When a frame has not finished decoding, always mark it as having alpha.
>> 
>> The comment was copied from ImageSource::frameHasAlphaAtIndex(size_t index)
> 
> The comment of ImageSource::frameHasAlphaAtIndex is long, so I pasted just summary of the comment to BitmapImage::frameHasAlphaAtIndex.
> 
> bool ImageSource::frameHasAlphaAtIndex(ImageFrame* buffer)
> {
>     // When a frame has not finished decoding, always mark it as having alpha.
>     // Ports that check the result of this function to determine their
>     // compositing op need this in order to not draw the undecoded portion as
>     // black.
>     // TODO: Perhaps we should ensure that each individual decoder returns true
>     // in this case.
>     return !frameIsCompleteAtIndex(buffer) || buffer->hasAlpha();
> }

You should add a line that said:
// See ImageSource::framehasAlphaAtIndex for explanation of why incomplete images claim to have alpha.

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