1186204 - make animations of transform with backface-visibility:hidden work on the compositor thread

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect)

Description

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

In bug 1186061 I'm going to disable compositor-thread (off-main-thread, OMT) animation of transform animations that have backface-visibility:hidden.

This bugs covers reenabling them, which I believe means detecting that the transform animation has crossed from showing the front face to showing the back face, and thus that we need to rerender.  This gets complicated in combination with preserve-3d (which we also don't support doing on the compositor).

Comment 1

[Matt Woodrow (:mattwoodrow)]

I don't think we need to rerender when we transition, since any 'backface' that is expected to become visible should be a separate element (with a separate layer).

I think we can get away with just having a flag specifying that the backface is hidden, and have the compositor cull the layer if necessary.

Comment 2

[Thinker Li [:sinker]]

According the discussion on a mail loop with dbaron and Matt, we are ready to move backface hidden and transform animation to the compositor.

Comment 3

[Markus Stange [:mstange]]

Cool! So what's necessary here? Just a layer flag for backface-visibility, and the LayerManagerComposite code to not render those layers if they face away from the camera?

Comment 4

[Matt Woodrow (:mattwoodrow)]

Does this not work already?

http://searchfox.org/mozilla-central/source/gfx/layers/composite/ContainerLayerComposite.cpp#202

Comment 5

[Markus Stange [:mstange]]

Oh! And the patch in bug 779598 already removes the backface-visibility check.

Comment 6

[Thinker Li [:sinker]]

The problem that this bug tried to fix had been fixed by other bugs.

Comment 7

[Hiroyuki Ikezoe (:hiro)]

Reopening since I am going to fix only preserve-3d case in bug 779598.

Comment 10

[Emilio Cobos Álvarez (:emilio)]

Hiro, do you know what exactly doesn't work here nowadays if we remove this check? Maybe WebRender deals fine with them?

Comment 11

[Hiroyuki Ikezoe (:hiro)]

The only one test case I could recall is animate-backface-hidden.html. I confirmed the test case works fine even without the check locally. So yeah, now we can drop the check.

Comment 13

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1186204 - Allow animations with backface-visibility: hidden to run in the compositor. r=#animation!

The check is not fully correct as per the comment (bug 779598 removed
the preserve-3d check).

I went through the relevant bugs and nothing misbehaves with this
afaict.

Comment 14

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/51c5d71d8ff4
Allow animations with backface-visibility: hidden to run in the compositor. r=firefox-animation-reviewers,devtools-reviewers,nchevobbe,boris

Comment 15

[Serban Stanca [:SerbanS]]

https://hg.mozilla.org/mozilla-central/rev/51c5d71d8ff4