[Webkit-unassigned] [Bug 3438] incorrect display of transparent 1x1 PNGs

[bugzilla-daemon at opendarwin.org]

http://bugzilla.opendarwin.org/show_bug.cgi?id=3438





------- Comment #11 from opendarwin.org at mitzpettel.com  2006-07-30 11:45 PDT -------
This bug turns out to be about premultiplied vs. non-premultiplied alpha! The
m_solidColor member of Image is supposed to be non-premul, but in
Image::checkForSolidColor() it is initialized from a premul bitmap context.

Dividing out by the alpha (if it's non-zero) in checkForSolidColor() fixes the
test case. A more straightforward approach (and more accurate, if the image
format is non-premul) would be to use a non-premul bitmap context, however when
I change the kCGImageAlphaPremultipliedLast to kCGImageAlphaLast in the
CGBitmapContextCreate I get a NULL context -- I have no idea why. Next thing
I'm going to try is use 8-bit unsigned instead of float components and see if
that changes anything.


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