1923846 - Support snapshotting individal pipelines off screen

Status: RESOLVED FIXED

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

Comment 1

[Nicolas Silva [:nical]]

Attachment: Bug 1923846 - Add a WebRender API to process pipelines offscreen. r=gw

The view-transition implementation needs a way to produce snapshots of various elements
before starting the transition without affecting the state of the current scene.
This commit makes this possible by adding the an "offscreen scene" concept to webrender.
Offscreen scenes are one-off scenes that are rendered immediately using a temporary frame
builder, temporary interners, etc. The only way that these offscreen scenes can have an
observable effect is by rendering snapshots into images of the resource cache which can
then be picked up by regular scenes.

To use the API:

• Create a pipeline.
• Build a display list for that pipeline containing snapshotted stacking contexts.
• Invoke Transaction::render_offscreen(pipelind_id).
• Delete the pipeline.

Long term it's worth revisiting whether this would be a good use case for the document API.
Some documents could be associated to a window while other documents remain off-screen.
Documents would have their own frame builder, interners and other retained states except for
the resource cache and gpu_caches that would be shared between all documents. Doing it this
way requires more work but would remove the need for a separate API and concept.

Comment 2

[Nicolas Silva [:nical]]

Attachment: Bug 1923846 - Allow WebRenderBridge to use an extra pipeline ID. r=#gfx-reviewers

This is quite the unsavory hack. For view-transition, the WR layer manager and bridge needs to be able to create a temporary pipeline without altering the one that is associated with the bridge and part of the scene that is being displayed. To do that the layer manager needs a pipeline Id to attach this premporary pipeline to, but allocating pipeline IDs is currently done in the main thread of the parent process and we can't afford the round-trip.
To work around this limitation, the patch makes it so that the pipeline IDs are effectively allocated in pairs. The even number is used for main pipeline ids, and the odd one can be used for temporary pipelines without risking collitions.

Ideally we would only allocate namespace ids (the upper 32 bits of the pipeline id) on the parent process main thread so that webrender bridges have the possibility to manage a large number of pipeline ids.

Comment 3

[Nicolas Silva [:nical]]

Attachment: Bug 1923846 - Render VT old-state snapshots offscreen without touching the main scene. r=emilio

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/454712144706
https://hg.mozilla.org/integration/autoland/rev/a88f72985079
Add a WebRender API to process pipelines offscreen. r=gw
https://github.com/mozilla-firefox/firefox/commit/9ef308540050
https://hg.mozilla.org/integration/autoland/rev/ff548f5b2ab2
Allow WebRenderBridge to use an extra pipeline ID. r=gfx-reviewers,lsalzman
https://github.com/mozilla-firefox/firefox/commit/67b387894754
https://hg.mozilla.org/integration/autoland/rev/0d38865e707a
Render VT old-state snapshots offscreen without touching the main scene. r=emilio
https://github.com/mozilla-firefox/firefox/commit/1b4e2aaa7e6f
https://hg.mozilla.org/integration/autoland/rev/3c76de70f9d9
apply code formatting via Lando

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/377e0e782805
https://hg.mozilla.org/integration/autoland/rev/f3ef179e4433
Revert "Bug 1923846: apply code formatting via Lando" for causing wr failures @ massive-element-below-and-on-top-of-viewport-partially-onscreen-old.html

Comment 6

[amarc]

Backed out for causing wr failures @ massive-element-below-and-on-top-of-viewport-partially-onscreen-old.html

• Backout link
• Push with failures
• Failure Log

Comment 7

[Nicolas Silva [:nical]]

Attachment: Bug 1923846 - Update test expectations. r=emilio

Something odd is happening on android specifically (the nothing-captured.html timeout is the worrying one).
This patch set contains important architectural changes for view-transition that I rather not block on the android failures, but it deserves followup investigations.

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/1e3669641284
https://hg.mozilla.org/integration/autoland/rev/38920927c798
Add a WebRender API to process pipelines offscreen. r=gw
https://github.com/mozilla-firefox/firefox/commit/62197b82b69f
https://hg.mozilla.org/integration/autoland/rev/433485a0ed73
Allow WebRenderBridge to use an extra pipeline ID. r=gfx-reviewers,lsalzman
https://github.com/mozilla-firefox/firefox/commit/0da0b0a10c2d
https://hg.mozilla.org/integration/autoland/rev/5a9f8ce554b5
Render VT old-state snapshots offscreen without touching the main scene. r=emilio
https://github.com/mozilla-firefox/firefox/commit/4c92c5b1115f
https://hg.mozilla.org/integration/autoland/rev/c0db14ee4a61
Update test expectations. r=emilio
https://github.com/mozilla-firefox/firefox/commit/253cbf632bd3
https://hg.mozilla.org/integration/autoland/rev/bc003754e55a
apply code formatting via Lando

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/69c4317b5b65
https://hg.mozilla.org/integration/autoland/rev/eb61a491850c
Revert "Bug 1923846: apply code formatting via Lando" for causing failures at massive-element-below-and-on-top-of-viewport-partially-onscreen-old.html.

Comment 10

[Atila Butkovits]

Backed out for causing failures at massive-element-below-and-on-top-of-viewport-partially-onscreen-old.html.

Backout link: https://hg-edge.mozilla.org/integration/autoland/rev/eb61a491850c367a4dec2de23bbfc2b82e15ecb3

Push with failures: https://treeherder.mozilla.org/jobs?repo=autoland&selectedTaskRun=fqmKsLA5SDuPWh1Y_--1Eg.0&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel&revision=bc003754e55a4e15693b175e44f88113e7cd8113

Failure log: https://treeherder.mozilla.org/logviewer?job_id=512235357&repo=autoland&lineNumber=2775

Comment 11

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/4b2420ec9831
https://hg.mozilla.org/integration/autoland/rev/35c6d1441032
Add a WebRender API to process pipelines offscreen. r=gw
https://github.com/mozilla-firefox/firefox/commit/6577b399dd00
https://hg.mozilla.org/integration/autoland/rev/93076b04b983
Allow WebRenderBridge to use an extra pipeline ID. r=gfx-reviewers,lsalzman
https://github.com/mozilla-firefox/firefox/commit/543d3cf67022
https://hg.mozilla.org/integration/autoland/rev/4c2f11d91585
Render VT old-state snapshots offscreen without touching the main scene. r=emilio
https://github.com/mozilla-firefox/firefox/commit/e29749965176
https://hg.mozilla.org/integration/autoland/rev/ab630cfe622b
Update test expectations. r=emilio
https://github.com/mozilla-firefox/firefox/commit/28d98d5c851a
https://hg.mozilla.org/integration/autoland/rev/83fa9cde3e29
apply code formatting via Lando

Comment 12

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/35c6d1441032
https://hg.mozilla.org/mozilla-central/rev/93076b04b983
https://hg.mozilla.org/mozilla-central/rev/4c2f11d91585
https://hg.mozilla.org/mozilla-central/rev/ab630cfe622b
https://hg.mozilla.org/mozilla-central/rev/83fa9cde3e29