1594364 - Protonmail text no longer using subpixel anti-aliasing where it does on Chrome

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect)

Description

[Kestrel]

Attachment: Protonmail text without subpixel anti-aliasing

STR:

1. With WebRender compositor on Ubuntu 19.10.
2. Go to https://protonmail.com
3. Inspect the text with a magnifying glass.

Text is using grayscale anti-aliasing instead of subpixel.

Does not happen with Basic compositor. Works on Chrome.

Regression range:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=26b8000a4954f3f9ee7c5b34f10a73843167fb06&tochange=60e6c61a7f455624b2ef0702d1925f8d8303bb38

Regressed by Bug 1590284.

Comment 2

[Jeff Muizelaar [:jrmuizel]]

This is a specific instance of the problem that we want to understand and perhaps deal with differently than bug 1593216

Comment 3

[Glenn Watson [:gw]]

Confirmed - will take this and work out what the differences are.

Comment 4

[Glenn Watson [:gw]]

Interestingly, Chrome decides not to create a compositor surface for the large(ish) fixed position images that show up during scrolling as a parallax effect. I'm not sure exactly what determines that yet - it does create a compositor surface for cases like https://reddit.com/r/rust, disabling subpixel AA in that case.

I prototyped not creating a compositor surface in WR for this case, and found that everything was being invalidated and rasterized every frame. Which led me to investigate and find the root cause - https://phabricator.services.mozilla.com/D52275. With that fix in place, when WR renders the protonmail page as a single compositor layer, the invalidation works as expected, just rasterizing the fixed position elements as you scroll past it. Once that lands, it will be much more feasible / efficient to not create compositor layers for fixed position elements in cases like this.

Comment 5

[Glenn Watson [:gw]]

Attachment: Bug 1594364 - Support subpx AA with picture caching in more cases.

Instead of creating a picture caching slice for any content that
is fixed position, also check if the clip(s) for the cluster are
fixed position or anchored to the scroll root.

This prevents WR creating slices for parallax style effects. There's
not much point in doing this anyway, since those slices will invalidate
due to the spatial node of the clip changing during scrolling. This
also allows subpixel AA to be enabled in more situations.

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/03ab38bbbd2e
Support subpx AA with picture caching in more cases. r=kvark

Comment 7

[Oana Pop-Rus]

https://hg.mozilla.org/mozilla-central/rev/03ab38bbbd2e