3D transform causes backdrop-filter effect to be applied incorrectly

• Component: Compositing
• Status: NEW ---

Created attachment 464973 [details]
Comparison between correct result in Chrome and the result in Epiphany.

How to reproduce: set both a 3D transform and a backdrop-filter on an element.

Live test: https://codepen.io/thebabydino/pen/oNMLELr

Live test with plane intersection: https://codepen.io/thebabydino/pen/vYzBPgd

I've only tested via Epiphany, but it's been confirmed it also happens in actual Safari - see replies with screenshots:

https://twitter.com/anatudor/status/1609985403251216387

https://mastodon.social/@anatudor/109621114959498459

Perhaps also relevant/ somewhat related to this other bug https://bugs.webkit.org/show_bug.cgi?id=249952

Another demo which looks broken because of this https://www.cssscript.com/demo/glassmorphism-credit-card/ - this demo in particular only uses `backdrop-filter` without a prefix so you're not going to see any blur effect at first, but if you add the prefix via DevTools, you're going to see the blurred backdrop area is incorrect during the animation/ if you also add a `transform: rotate(45deg)` on the `.card` element.

[Matt Woodrow]

It looks like the second test case is a slightly different issue, the preserve-3d isn't applied because the child is a pseudo element.

Filed https://bugs.webkit.org/show_bug.cgi?id=252277 for that issue.

Here's a test of the intersection with spans instead of pseudos https://codepen.io/thebabydino/pen/BaOaEbj

And a cube-cube intersection test https://codepen.io/thebabydino/pen/XWProEq

This last one is how I actually came across this problem, as I was trying to get the intersecting glassy cubes effect like https://www.pinterest.com/pin/432838214178310878/

[Radar WebKit Bug Importer]

<rdar://problem/105690050>

[Michael Catanzaro]

If the bug happens in Safari too, then this shouldn't be assigned to WebKitGTK component. That reduces the chance of the right people looking.

[Simon Fraser (smfr)]

Created attachment 468193 [details]
macOS screenshot