Kartikaya Gupta (email:kats@mozilla.staktrace.com) Assignee
	Description • 7 years ago

With WR+APZ enabled, the layout/reftests/async-scrolling/split-opacity-layers-1.html reftest fails [1]. It looks like one of the purple divs is 10 pixels off from where it should be.

I was able to modify the scrolling example in webrender to reproduce a similar scenario. It looks like webrender internally treats a "None" transform differently from a "Some(PropertyBinding::Value(LayoutTransform::identity()))" transform. Right now we pretty much always use the identity transform on stacking contexts but maybe we shouldn't be? See bug 1345577.

[1] https://treeherder.mozilla.org/#/jobs?repo=try&revision=68c5c545d47a35f45b6af5c79dcf2e6e59c00bf3&selectedJob=102461411

	Kartikaya Gupta (email:kats@mozilla.staktrace.com) Assignee
	Comment 1 • 7 years ago

I filed servo/webrender#1304 for the issue since it seems like unexpected behaviour in WR.

	Kartikaya Gupta (email:kats@mozilla.staktrace.com) Assignee
	Comment 2 • 7 years ago

Hacking it up so that identity transforms get turned into "None" fixed the test for me locally. I did a try push to see what else changes: https://treeherder.mozilla.org/#/jobs?repo=try&revision=5b8d2a2cfb0db0016aee29e08af1b913df67ed10

	Kartikaya Gupta (email:kats@mozilla.staktrace.com) Assignee
	Comment 3 • 7 years ago

The patch fixes the split-opacity-layers-1.html test as expected, and doesn't appear to affect any other test. All the other failures are exactly the same as without this patch.

	Kartikaya Gupta (email:kats@mozilla.staktrace.com) Assignee
	Comment 4 • 7 years ago

I realized that we have another PushStackingContext codepath which this didn't affect. I should fix that one too.

	Peter Chang[:pchang]
	Comment 7 • 7 years ago
mozreview-review

Comment on attachment 8873170 [details]
Bug 1368551 - Remove unneccessary overload of PushStackingContext.

https://reviewboard.mozilla.org/r/144640/#review148618

	Peter Chang[:pchang]
	Comment 8 • 7 years ago
mozreview-review

Comment on attachment 8873171 [details]
Bug 1368551 - Don't send transforms to WR in push_stacking_context if they are identity.

https://reviewboard.mozilla.org/r/144642/#review148626

	Pulsebot
	Comment 9 • 7 years ago

Pushed by kgupta@mozilla.com:
https://hg.mozilla.org/projects/graphics/rev/85e598624e0f
Remove unneccessary overload of PushStackingContext. r=pchang
https://hg.mozilla.org/projects/graphics/rev/67f689dd202d
Don't send transforms to WR in push_stacking_context if they are identity. r=pchang

	Ryan VanderMeulen [:RyanVM]
	Comment 10 • 7 years ago
bugherder

https://hg.mozilla.org/mozilla-central/rev/85e598624e0f
https://hg.mozilla.org/mozilla-central/rev/67f689dd202d