1573893 - backdrop-filter disables subpixel AA for elements inside a backdrop

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect, P3)

Description

[Connor Brewster [:cbrewster]]

Any elements that are in the backdrop of an element with backdrop-filter will get rendered to an intermediate surface. In WebRender, we aren't sure if the intermediate surface will be opaque, so subpixel AA is disabled.
https://searchfox.org/mozilla-central/rev/c7e8bc4996f979e5876b33afae3de3b1ab4f3ae1/gfx/wr/webrender/src/picture.rs#2957

Comment 1

[Tynach]

I just want to say that it's good to see this actually being marked as blocking #1578503. Chrome used to not do this, allowing subpixel antialiasing of text underneath a backdrop-filtered element.. Then at some point it stopped supporting that for some reason, rendering the text as grayscale instead.

Even if that same decision might end up prevailing here in Firefox, I'm glad that Firefox is - at the very least - considering the idea of making it a goal, even to the point of labeling it as a bug that blocks the use of backdrop-filter being enabled by default in the mainline release.

Comment 2

[Glenn Watson [:gw]]

This is no longer an issue with the updated implementation - text that is on a picture cache which is part of a backdrop-filter effect will know whether it's opaque and should select subpixel in this case.