[Webkit-unassigned] [Bug 192554] [GTK][WPE] Rendering artifact on subpixel positions

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=192554

Olivier Blin <olivier.blin at softathome.com> changed:

           What    |Removed                     |Added
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                 CC|                            |cgarcia at igalia.com

--- Comment #28 from Olivier Blin <olivier.blin at softathome.com> ---
We had multiple issues to build a reference image that was suitable for the Mac test runners as well.

The GTK test runner always output images in the 800x600 resolution, with no alpha channel.
In the first iteration, the test case gave on Mac a test result in the 1600x1200 resolution, so the test had to be updated to give a 800x600 output on Mac too, by avoid using a 100% size on the body.

Then there was an issue with the alpha channel, because the reference image was generated with the GTK test runner, which never adds an alpha channel in the PNG image if there is no transparent pixel (this is the behavior of the PNG writer in the cairo library).
But the Mac test runner appears to always add an alpha channel, so the images did not match.
We had to tweak a local build of the cairo library to always generate an alpha channel.

This is all to add a test case because we noticed a rounding mismatch between the layout and painting when accelerated compositing is used.

We would appreciate a feedback regarding the behavior on the Mac port.
Is the issue reproduced as well?

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