1829186 - Scroll root detection broken in presence of backdrop filter

Status: NEW

(Core :: Graphics: WebRender, defect)

Description

[Jamie Nicol [:jnicol]]

See this test case from bug 1809738, with gfx.webrender.debug.picture-caching enabled. At the time this showed how backdrop filter means we cannot put the fixed position items on a separate slice than the scrollable content. Which is expected with backdrop filter.

However, since then, scroll root detection is entirely broken. The slice is not scrollable, meaning the entire page is invalidated on scroll. This was regressed by bug 1800358. Glenn, do you know whether we can fix this without reintroducing the bug that fixed?

This affects both desktop and android.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1800358

Comment 2

[Glenn Watson [:gw]]

I'm not sure without spending some more time investigating the specific case. I do vaguely recall at the time of fixing that regression thinking that the fix is conservative, and could be relaxed with some more careful analysis though, so it's likely we can fix it. I'll need to try and find some time to take a detailed look.

Comment 3

[BugBot [:suhaib / :marco/ :calixte]]

The severity field is not set for this bug.
:gw, could you have a look please?

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