1463313 - Canvas updates are delayed by a frame if the canvas is the only thing that changes

Status: RESOLVED FIXED

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

Description

[Markus Stange [:mstange]]

Attachment: testcase 1: canvas updates on mousemove

In this testcase, as you move your mouse over the grey rectangle, the green square should always be under the mouse cursor. However, with WebRender enabled, it frequently lags behind.

I noticed this when interacting with the flame graph in perf.html.

This problem does not seem to occur if other page content changes at the same time, as demonstrated by the second testcase.

Comment 1

[Markus Stange [:mstange]]

Attachment: testcase 2: canvas and page update on mousemove

Comment 2

[Sotaro Ikeda [:sotaro]]

async-scene-build seems to be related. When I set "gfx.webrender.async-scene-build;0". I did not saw the delay.

Comment 3

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

A guess as to what's happening here is that we get a RecvUpdateResources and send a transaction with the updates at [1], but that gets processed on the scene builder thread. There's nothing that triggers a composite after that. There is some code at [2] that does it, but that only gets invoked in the case where there was a new scene built, which doesn't happen if it's just a resource update.

[1] https://searchfox.org/mozilla-central/rev/2aa42f2cab4a110edf21dd7281ac23a1ea8901f9/gfx/layers/wr/WebRenderBridgeParent.cpp#467
[2] https://searchfox.org/mozilla-central/rev/2aa42f2cab4a110edf21dd7281ac23a1ea8901f9/gfx/webrender_bindings/src/bindings.rs#729

Comment 4

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

This seems to fix it for me locally, which confirms comment 3: https://treeherder.mozilla.org/#/jobs?repo=try&revision=4f5047f7ea31f7c23dfa3f56e0cc5eb8913009b8

Comment 5

[David Bolter [:davidb] (NeedInfo me for attention)]

Batch updating status flags based on WR schedule - please adjust if needed.

Comment 6

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

This should be fixed in the next nightly.