1505363 - Animated element sometimes flashes at the end of the animation

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect, P4)

Description

[Nicolas Chevobbe [:nchevobbe]]

Attachment: end of animation glitch

**Steps to reproduce**
1. Go to `data:text/html,<meta charset=utf8><style>h1 {animation: 1.1s linear appears;}@keyframes appears {0% {opacity: 0;}100% {opacity: 1;}}</style><h1>Hello</h1>`


**Expected results**

The "Hello" text slowly appears. At the end of the animation, the text stays visible

**Actual results**

Sometimes, there's a flash at the end of the animation (see attached screencast, at 2-3s).
You can reload the tab a few times, I usually reproduce this in 3 tries.
This only seems to happen with webRender enabled

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Comment 1

[Jeff Muizelaar [:jrmuizel]]

What platform do you see this on?

Comment 2

[Nicolas Chevobbe [:nchevobbe]]

OSX

Comment 3

[Sotaro Ikeda [:sotaro]]

I tried the STR in comment 0 with latest nightly on osx, win10 and linux, but could not reproduce the problem.

Comment 4

[Sotaro Ikeda [:sotaro]]

It might be similar to Bug 1497852.

Comment 5

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

Getting a WR capture here would probably help. Might not be too hard to modify the code to just grab a capture for every frame in an OMTA and then just pick out the bad frame.

Comment 6

[Jeff Muizelaar [:jrmuizel]]

Nicolas, can you reproduce this problem on Windows?

Comment 7

[Sotaro Ikeda [:sotaro]]

I could reproduce the problem by adding latency in LowPrioritySceneBuilder::process_transaction() from it. The problem seemed to be caused by async animation.

Comment 8

[Sotaro Ikeda [:sotaro]]

Attachment: temporal patch - Add latency to LowPrioritySceneBuilder::process_transaction()

Comment 9

[Sotaro Ikeda [:sotaro]]

With attachment 9034650 [details] [diff] [review] , I reproduce  the parobem with STR in comment 0.

And when I disabled async animation by pref layers.offmainthreadcomposition.async-animations:false, I did not see the problem.

Comment 10

[Sotaro Ikeda [:sotaro]]

WebRenderBridgeParent::RemoveEpochDataPriorTo() seems to delete animation too early.

WebRenderLayerManager::DiscardCompositorAnimations() was called just before calling WrBridge()->EndTransaction() in WebRenderLayerManager::EndTransactionWithoutLayer(). Then WebRenderBridgeParent::RecvDeleteCompositorAnimations() was called just before WebRenderBridgeParent::RecvSetDisplayList() call. The RecvSetDisplayList() update WrEpoch. Then the RecvDeleteCompositorAnimations() stored old epoch in mCompositorAnimationsToDelete.

https://dxr.mozilla.org/mozilla-central/source/gfx/layers/wr/WebRenderBridgeParent.cpp#778

Comment 11

[Sotaro Ikeda [:sotaro]]

It seems better to call WebRenderLayerManager::DiscardCompositorAnimations() after calling WrBridge()->EndTransaction() in WebRenderLayerManager::EndTransactionWithoutLayer().

Comment 12

[Sotaro Ikeda [:sotaro]]

Attachment: Bug 1505363 - Call DiscardCompositorAnimations() after calling WrBridge()->EndTransaction()

Comment 13

[Nicolas Chevobbe [:nchevobbe]]

> Nicolas, can you reproduce this problem on Windows?

I tried with the STR, reloading the page ~50 times and couldn't reproduce it.

Comment 14

[Sotaro Ikeda [:sotaro]]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=24d4765ec7689757f8c9660c4d4268f0b56f5429

Comment 15

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/ed51ef14289e
Call DiscardCompositorAnimations() after calling WrBridge()->EndTransaction() r=kats

Comment 16

[Oana Pop-Rus]

https://hg.mozilla.org/mozilla-central/rev/ed51ef14289e