1723469 - Background image larger than 4096px ignore CSS opacity

Status: RESOLVED FIXED

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

Description

[Romuald Brunet]

Attachment: HTML example reproducing the issue

Description

When a CSS element have an image whose background-image is an image larger than 4096 pixels (in height at least), the opacity CSS attribute is somehow ignored.

Any value more than 0.0 will be displayed with an actual opacity of 1.0

• when using a CSS definition with an image of 4096px height and 0.3 opacity, the opacity correctly displayed
• when using a CSS definition with an image of 4097px height and 0.3 opacity, the opacity is set to 1.0

I've attached an HTML page showing the issue

---

Additional information

This is a regression, as this works fine in Firefox 78 (ESR)

This seems to affect all platforms

For some reason, adding a visible text (not space for example) inside the element will circumvent the issue and take the opacity into account

(Actual use case is CSS sprites image whose width / height can be very large)

Comment 1

[Romuald Brunet]

Attachment: Example reproducing the issue (images included)

Included the actual images as data-url as the original ones obviously weren't included >_<

Comment 2

[Romuald Brunet]

The example can also be found at https://chivil.com/bugs/firefox-background-opacity/

Comment 3

[Krzysztof]

Mozregression says that it's regression from bug 1669840.

Comment 4

[Brad Werth [:bradwerth]]

I'll figure out what we can do here. Likely we're hitting some texture limit in WebRender that puts us on a fallback path that handles opacity differently.

Comment 5

[Lee Salzman [:lsalzman]]

I would suspect something to do with image tiling?

Comment 6

[Jan Honza Odvarko [:Honza] (always need-info? me)]

Hi Brad, any chance to look at this one (and perhaps also triage)?
Thank you!

Comment 7

[Brad Werth [:bradwerth]]

Sorry for the lack of action on this. I'll stay on it; just need to complete some other things first.

Comment 8

[Lougenia Bailey]

:bradwerth is this still a priority?

Comment 9

[Brad Werth [:bradwerth]]

(In reply to Lougenia Bailey from comment #8)

:bradwerth is this still a priority?

P3 is still appropriate. I have higher-priority bugs assigned to me.

Comment 11

[Ryan VanderMeulen [:RyanVM]]

Hi Brad, any chance we can revisit the priority of this bug? It appears to have picked up a dupe recently and is hitting in the wild.

Comment 12

[Brad Werth [:bradwerth]]

Comment on attachment 9234227 [details]
HTML example reproducing the issue

The other reproduction case is self-contained.

Comment 13

[Brad Werth [:bradwerth]]

Attachment: Bug 1723469 Part 1: Prevent large background images from using opacity flattening.

This prevents opacity from being set on large images sent to WebRender.
Instead, opacity will be handled in the parent layer, which is less efficient,
but correct for these large images.

This can be a temporary fix until WR supports opacity on arbitrarily large
images.

Comment 14

[Brad Werth [:bradwerth]]

Still need to add a test, and a dependent Bug for a better fix within WebRender.

Comment 15

[Brad Werth [:bradwerth]]

Attachment: Bug 1723469 Part 2: Add reftest for opacity flattening of large images.

Depends on D137360

Comment 17

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/01e61a4cc0af
Part 1: Prevent large background images from using opacity flattening. r=aosmond,emilio
https://hg.mozilla.org/integration/autoland/rev/086ba0886b3f
Part 2: Add reftest for opacity flattening of large images. r=aosmond,emilio

Comment 18

[Andreea Pavel [:apavel]]

https://hg.mozilla.org/mozilla-central/rev/01e61a4cc0af
https://hg.mozilla.org/mozilla-central/rev/086ba0886b3f

Comment 19

[Brad Werth [:bradwerth]]

Post-landing comments on https://phabricator.services.mozilla.com/D137360 revealed a flaw that needs patching.

Comment 20

[Brad Werth [:bradwerth]]

Attachment: Bug 1723469 Part 3: Calculate WR images limits in dev pixels.

WebRender doesn't care about CSS scale, so calculate its limits in terms of
the scale it does care about.