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<body><span class="vcard"><a class="email" href="mailto:magomez@igalia.com" title="Miguel Gomez <magomez@igalia.com>"> <span class="fn">Miguel Gomez</span></a>
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<a class="bz_bug_link
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title="NEW - REGRESSION(r205841): [GTK] Test fast/images/animated-png.html is failing since r205841"
href="https://bugs.webkit.org/show_bug.cgi?id=168425">bug 168425</a>
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<td>sabouhallawa@apple.com
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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - REGRESSION(r205841): [GTK] Test fast/images/animated-png.html is failing since r205841"
href="https://bugs.webkit.org/show_bug.cgi?id=168425#c3">Comment # 3</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - REGRESSION(r205841): [GTK] Test fast/images/animated-png.html is failing since r205841"
href="https://bugs.webkit.org/show_bug.cgi?id=168425">bug 168425</a>
from <span class="vcard"><a class="email" href="mailto:magomez@igalia.com" title="Miguel Gomez <magomez@igalia.com>"> <span class="fn">Miguel Gomez</span></a>
</span></b>
<pre>Once I found the fix for the animation not running, I've been debugging why one of the images of the test fails. The problem seems to be how alpha premultiplied components are calculated.
Before r205841, premultiplied alpha components were calculated in PNGImageDecoder::setPixelPremultipliedRGBA as
fastDivideBy255(colorComponent * alpha);
But after r205841 this was moved to Color::premultipliedChannel, where it's calculated as
fastDivideBy255(colorComponent * alpha + 254);
which is not producing the same result as before the changes. This seems to be causing problems with animations that blend frames into the previous ones.
I'm not sure why 254 is added for the calculation. I've always seen it as just colorComponent * alpha, so I may be missing something here. Said, what do you think?</pre>
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