1957806 - `backdrop-filter` and `mix-blend-mode` affect subpixel text antialiasing differently

Status: UNCONFIRMED

(Core :: Graphics: WebRender, defect)

Description

[Bartosz Dziewoński]

Steps to reproduce:

See attached test cases and screenshots (scaled 8x for convenience).

Actual results:

backdrop-filter and mix-blend-mode affect subpixel text antialiasing differently.

mix-blend-mode disables subpixel AA for the affected elements, which is the correct behavior.

backdrop-filter does not disable subpixel AA, which results in incorrect text rendering for some operations.

Expected results:

I would expect the two attached test cases to render pixel-to-pixel identical. One of them has an element with backdrop-filter: invert(); background: transparent; and the other with mix-blend-mode: difference; background: white;.

Comment 1

[Bartosz Dziewoński]

Attachment: subpixel-aa-backdrop-filter.html

Comment 2

[Bartosz Dziewoński]

Attachment: subpixel-aa-mix-blend-mode.html

Comment 3

[Bartosz Dziewoński]

Attachment: firefox_subpixel-aa-backdrop-filter.png

Comment 4

[Bartosz Dziewoński]

Attachment: firefox_subpixel-aa-mix-blend-mode.png

Comment 5

[Bartosz Dziewoński]

Chrome behaves differently in this test case, but I believe its behavior is also incorrect. See https://issues.chromium.org/issues/407785181

Comment 6

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

The Bugbug bot thinks this bug should belong to the 'Core::Graphics: WebRender' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 7

[Sotaro Ikeda [:sotaro]]

:gw, can you comment to this bug?