1976163 - Banding in linear gradient even when WebRender dithering is enabled

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect)

Description

[Sotaro Ikeda [:sotaro]]

Banding is perceived in linear gradient even when WebRender dithering is enabled.

Comment 1

[Sotaro Ikeda [:sotaro]]

Attachment: linear-gradient.html

Comment 2

[Sotaro Ikeda [:sotaro]]

When Attachment 9499116 [details] is shown with large window, the linear gradient rendering was repeatedly darkens and lightens slightly.

Comment 3

[Sotaro Ikeda [:sotaro]]

Attachment: screenshot

Comment 4

[Sotaro Ikeda [:sotaro]]

Attachment: enlarge part of screenshot

Comment 5

[Sotaro Ikeda [:sotaro]]

Regression window

10:04.66 INFO: Got as far as we can go bisecting nightlies...
10:04.66 INFO: Last good revision: 79514ae28ef4b3508baf56fc8e89ef593a9b77b1 (2020-01-21)
10:04.66 INFO: First bad revision: ed735c504092d21e78ecf5cb4debf5faecb4c4ab (2020-01-22)
10:04.66 INFO: Pushlog:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=79514ae28ef4b3508baf56fc8e89ef593a9b77b1&tochange=ed735c504092d21e78ecf5cb4debf5faecb4c4ab

Bug 1608741 seemed to cause the regression.

Comment 6

[Sotaro Ikeda [:sotaro]]

Attachment: screenshot.png

Comment 7

[Sotaro Ikeda [:sotaro]]

Attachment: enlarge_part_of_screenshot.png

Comment 8

[BugBot [:suhaib / :marco]]

:gw, since you are the author of the regressor, bug 1608741, could you take a look? Also, could you set the severity field?

For more information, please visit BugBot documentation.

Comment 9

[Sotaro Ikeda [:sotaro]]

Bug 1608741 disabled dithering. But re-enabling dithering with pref gfx.webrender.dithering = true did not address the problem.

Comment 10

[Sotaro Ikeda [:sotaro]]

The problem existed even with taking snapshot. The snapshot does not use WebRender for rendering.

Comment 11

[Glenn Watson [:gw]]

Nical might have more idea what we're seeing in this case.

Comment 12

[Sotaro Ikeda [:sotaro]]

I am not sure yet if the problem is an artifact or a banding as in the following.

• https://github.com/servo/webrender/issues/929

Comment 13

[Sotaro Ikeda [:sotaro]]

(In reply to Sotaro Ikeda [:sotaro] from comment #12)

I am not sure yet if the problem is an artifact or a banding as in the following.

• https://github.com/servo/webrender/issues/929

Ah, it is just a perception. By using color picker app, color was changed correctly. And WebRender dithering did not address the banding perception.

Comment 14

[Sotaro Ikeda [:sotaro]]

Attachment: temporal patch - force brush shader for linear gradient

Comment 15

[Sotaro Ikeda [:sotaro]]

With Attachment 9499392 [details] [diff], when brush shader is used for linear gradient instead of cached shader, the dithering seemed to work as expected.

Comment 16

[Sotaro Ikeda [:sotaro]]

Optimization of LinearGradientTemplate::from() caused the problem for dithering.

Comment 17

[Sotaro Ikeda [:sotaro]]

Attachment: Bug 1976163 - Disable optimization of linear gradient in LinearGradientTemplate::from() when dithering is enabled

Comment 18

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/486f1e707607
https://hg.mozilla.org/integration/autoland/rev/3bf6c55941a1
Disable optimization of linear gradient in LinearGradientTemplate::from() when dithering is enabled r=gfx-reviewers,gw

Comment 19

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/777be8b6b88e
https://hg.mozilla.org/integration/autoland/rev/44aa76ccd422
Revert "Bug 1976163 - Disable optimization of linear gradient in LinearGradientTemplate::from() when dithering is enabled r=gfx-reviewers,gw" for causing wrench bustages

Comment 20

[amarc]

Backed out for causing wrench bustages

• Backout link
• Push with failures
• Failure Log

Comment 21

[Sotaro Ikeda [:sotaro]]

Addressed wrench test failure.
https://treeherder.mozilla.org/jobs?repo=try&revision=ea126c085045e17ae58db6ec13aed3295e31ab25

Comment 22

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/3ef5c6dd71df
https://hg.mozilla.org/integration/autoland/rev/84d3a58e6897
Disable optimization of linear gradient in LinearGradientTemplate::from() when dithering is enabled r=gfx-reviewers,gw

Comment 23

[Serban Stanca [:SerbanS]]

https://hg.mozilla.org/mozilla-central/rev/84d3a58e6897