Bug 103424 – [Qt] A new compositing bug uncovered by r135859

• Status: RESOLVED
• Resolution: INVALID
• Component: New Bugs

[Csaba Osztrogonác]

fast/backgrounds/background-opaque-images-over-color.html started to
fail on Qt after r135859 and r135861 - refactoring to reftest

See https://bugs.webkit.org/show_bug.cgi?id=103275 for details.

Image diff on the Qt bot: http://build.webkit.sed.hu/results/x86-64%20Linux%20Qt%20Release/r135862%20%2845465%29/fast/backgrounds/background-opaque-images-over-color-diffs.html

[Csaba Osztrogonác]

I skipped it by r135865. Please unskip it with the proper fix.

[Allan Sandfeld Jensen]

It seems to be case 3 and case 8 that that fails.

  <div id="case_3" class="redBack" style="background-image: -webkit-cross-fade(url(../../http/tests/multipart/resources/green-100x100.png), url(../../http/tests/multipart/resources/green-100x100.png), 50%)"></div>

   <div id="case_9" class="redBack" style="background-repeat: no-repeat; background-image: url(../../http/tests/multipart/resources/green-100x100.png),url(resources/64x32-red.png)"></div>

 So it appears cross-fading between two identical images produces something that is not an identical image.

[Allan Sandfeld Jensen]

A quick investigation shows that cross-fading images is crossplatform code. It does however rely on a PLUS composition to ensure the two images opacity adds up to 100%. It could appear that QPainter does not composition opacity values set by QPainter::setOpacity but only thoses in the alpha values of painted images.

[Jocelyn Turcotte]

=== Bulk closing of Qt bugs ===

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