Bug 246590 – REGRESSION (r278062): Multiple backgrounds with "background-blend-mode: difference" breaks

• Status: RESOLVED
• Resolution: FIXED
• Component: Layout and Rendering

Created attachment 463015 [details]
Screenshot showing lines instead of checkerboard

Steps to reproduce:

*(ios16+) Go to: https://codepen.io/jokeyrhyme/pen/OVVzem

Expected result:

*Result should display a checkerboard pattern

Actual result:

*In the codepen result, only one background is displayed, rendering lines only. See screenshot from ios 16


Additional info:

This displays as a checkerboard in Firefox, Chrome and on iOS 15.7 but appears broken in iOS 16 so I would consider it a regression bug.
Don't know if/how it may affect other areas of using multiple backgrounds using "linear-gradient" and "background-blend-mode: difference"

[Radar WebKit Bug Importer]

<rdar://problem/101257606>

[Said Abou-Hallawa]

This happens on macOS also.

[Said Abou-Hallawa]

I think this is a regression of r278062.

This revision replaced the call to GraphicsContextCG::setPlatformCompositeOperation() by GraphicsContext::setCompositeOperation() in GraphicsContextCG::drawPattern(). setCompositeOperation() is platform independent and should not be called from GraphicsContextCG methods. Instead we should be calling GraphicsContextCG::setCGBlendMode(). 

Note: r280095 fixed a similar problem in drawNativeImage().

[Said Abou-Hallawa]

Pull request: https://github.com/WebKit/WebKit/pull/6280

[EWS]

Committed 256578@main (9ffcb90d8fa7): <https://commits.webkit.org/256578@main>

Reviewed commits have been landed. Closing PR #6280 and removing active labels.