1543974 - Allow reusing render tasks within a frame

Status: RESOLVED FIXED

Description

[Nicolas Silva [:nical]]

There can currently be only one render task reading the input of another task in the render task tree.

We want to be able to have several tasks read the output of another task (effectively turning the render task tree into a render task graph), in order to perform some optimizations such as reusing intermediate work when an item has multiple shadows, and efficiently expressing SVG filter graphs.

Comment 1

[Nicolas Silva [:nical]]

Attachment: Bug 1543974 - Deal with conflicting render task rect scheduling and allocation. r=gw,kvark

Due to the render task ping-pong target allocation scheme, we need to ensure:

• that tasks only read from tasks that are an odd number of passes apart,
• that render task content is kept valid long enough for all of the dependent tasks.

The former is solved in this patch through blit tasks, the latter by marking tasks for saving as needed.

Comment 2

[Nicolas Silva [:nical]]

Attachment: render task graph with shadow stacks

Screenshot of wrench with a stack of 4 shadows and the generated render task graph. Two shadows with identical radii (so they share all render tasks), one with a slightly higher radius that can reuse both down-scale passes but needs its own blur passes, and one with a smaller radius using a single downscale and a blit to resolve the allocation conflict.

Comment 3

[Nicolas Silva [:nical]]

Attachment: Bug 1543974 - Add render task scheduling tests. r=gw

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5cba75dd63c2
Deal with conflicting render task rect scheduling and allocation. r=kvark

Comment 5

[Oana Pop-Rus]

https://hg.mozilla.org/mozilla-central/rev/5cba75dd63c2

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/8f066e5c42c8
Add render task scheduling tests. r=gw

Comment 7

[Alexandru Michis [:malexandru]]

Backed out changeset 8f066e5c42c8 (Bug 1543974) for causing bustages on webrender builds

Backout link: https://hg.mozilla.org/integration/autoland/rev/bfeb8f1e42e35f32fe2f4382962c3586336b5b33

Push with failures: https://treeherder.mozilla.org/#/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception&revision=8f066e5c42c8d093eca140056720b3808065f7e7

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/2bcdd7ab7d95
Add render task scheduling tests. r=gw

Comment 9

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/2bcdd7ab7d95