[Webkit-unassigned] [Bug 133842] [CSS Blending] Rendering defects when using background-blend-mode on a radial-gradient background image

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=133842





--- Comment #5 from Ion Rosca <rosca at adobe.com>  2014-06-16 09:20:06 PST ---
I did a bit of investigation and it might be a CG issue. I'll describe the attached tests and what happens.

"Test with body"
* html: the body element has a background color (aqua), a radial-gradient image (a yellow oval) and background-blend-mode.
* result: the yellow oval drawn over a background being random content from other tabs (see "Screenshot blending on body")

"Test with divs"
* html: div elements have background color (aqua), radial-gradient image (yellow circle) and background-blend-mode.
* result: almost all divs (except those having normal and screen blend modes) contain a yellow circle on a white background.

Debugging:
* Everything up to CGContextDrawRadialGradient paints correctly (the aqua background color). 
* calling any CGContextFillRect function right before CGContextDrawRadialGradient will have no effect,  because the latter replaces everything on the viewport.
* calling CGContextFillRect with a red color right after CGContextDrawRadialGradient will draw the red rectangle, blending it correctly with the yellow gradient and other content in the viewport.

Exceptions:
* I could not reproduce "Test with body" on Safari 8, Mac OS 10.10, but "Test with divs" is still there.
* Screen blend mode works everywhere.
* Adding a css border on divs having background-blend-mode in the "Test with divs" file fixes the issue for this test case.
* It works correctly in minibrowser.

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