1401898 - background-blend-mode chooses wrong backdrop color to blend in WR Layer-free mode

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, enhancement, P1)

Description

[Kevin Chen[:kechen] (UTC + 8)]

There is a try failure[1] when we enable nsDisplayBackgroundImage image in Bug 1359242.

The reason is that, when WR layer-free is enabled, we blend the background image with the color of elements behind it which, according to spec[2], we shouldn't.

[1] https://treeherder.mozilla.org/#/jobs?repo=try&revision=1ddb2fd73588d1c76b1b3dadb8f5964dd0b3dfed&selectedJob=131243114
[2] https://drafts.fxtf.org/compositing-1/#background-blend-mode

Comment 1

[Kevin Chen[:kechen] (UTC + 8)]

Attachment: Bug 1401898 - Add root StackingContext for WebRenderCommandBuilder which prevents Webrender from treating the first StackingContext as page root and setting the wrong isolation mode;

Review commit: https://reviewboard.mozilla.org/r/186714/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/186714/

Comment 2

[Kevin Chen[:kechen] (UTC + 8)]

The problem is that the first StackingContext pushed to Webrender will be treated as the page group[2]; however, this kind of StackingContext is not pushed by gecko so I added one here.

[1] https://github.com/servo/webrender/blob/29d325f54bbead84e97dcf7dc536463c45f8eece/webrender/src/frame_builder.rs#L388
[2] https://www.w3.org/TR/compositing-1/#pagebackdrop

Comment 3

[Kartikaya Gupta (email:[e-mail])]

Hm, this used to happen as part of wr_dp_begin but I guess at some point along the way we disconnected that piece of code...

Comment 4

[Jeff Muizelaar [:jrmuizel]]

Comment on attachment 8915503 [details]
Bug 1401898 - Add root StackingContext for WebRenderCommandBuilder which prevents Webrender from treating the first StackingContext as page root and setting the wrong isolation mode;

I'm not familiar enough with this. I'll let kats try.

Comment 5

[Kartikaya Gupta (email:[e-mail])]

Comment on attachment 8915503 [details]
Bug 1401898 - Add root StackingContext for WebRenderCommandBuilder which prevents Webrender from treating the first StackingContext as page root and setting the wrong isolation mode;

https://reviewboard.mozilla.org/r/186714/#review191968

This seems fine to me. In a separate bug or patch we should get rid of the three unused arguments to StackingContextHelper's constructor.

Comment 6

[Mozilla Autoland]

We're sorry, Autoland could not rebase your commits for you automatically. Please manually rebase your commits and try again.

hg error in cmd: hg rebase -s 6953c82f7d0c -d 5b41d7a0fe73: rebasing 424501:6953c82f7d0c "Bug 1401898 - Add root StackingContext for WebRenderCommandBuilder which prevents Webrender from treating the first StackingContext as page root and setting the wrong isolation mode; r=kats" (tip)
merging gfx/layers/wr/WebRenderCommandBuilder.cpp
warning: conflicts while merging gfx/layers/wr/WebRenderCommandBuilder.cpp! (edit, then use 'hg resolve --mark')
unresolved conflicts (see hg resolve, then hg rebase --continue)

Comment 7

[Kevin Chen[:kechen] (UTC + 8)]

Comment on attachment 8915503 [details]
Bug 1401898 - Add root StackingContext for WebRenderCommandBuilder which prevents Webrender from treating the first StackingContext as page root and setting the wrong isolation mode;

Review request updated; see interdiff: https://reviewboard.mozilla.org/r/186714/diff/1-2/

Comment 8

[Kartikaya Gupta (email:[e-mail])]

Comment on attachment 8915503 [details]
Bug 1401898 - Add root StackingContext for WebRenderCommandBuilder which prevents Webrender from treating the first StackingContext as page root and setting the wrong isolation mode;

https://reviewboard.mozilla.org/r/186714/#review192696

Comment 9

[Mozilla Autoland]

We're sorry - something has gone wrong while rewriting or rebasing your commits. The commits being pushed no longer match what was requested. Please file a bug.

Comment 10

[Kartikaya Gupta (email:[e-mail])]

I'll just land this by hand along with the other patch.

Comment 11

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/6b7fbf00410e
Add root StackingContext for WebRenderCommandBuilder which prevents Webrender from treating the first StackingContext as page root and setting the wrong isolation mode; r=kats

Comment 12

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/6b7fbf00410e