847286 - layers conflate OMTA animation generation from transitions and from animations

Status: RESOLVED FIXED

(Core :: Graphics: Layers, defect)

Description

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

While doing code inspection in order to fix bug 822721, I noticed an issue with the animation generation member of Layer.

The purpose of the animation generation is for us to known whether we need to send new information to the layer tree from the style system.

I *think* (though I don't entirely remember) that it's possible for a element that is simultaneously undergoing both animations and transitions to end up with a different animation generation on its ElementTransitions and its ElementAnimations.  If that happens, then AddAnimationsAndTransitionsToLayer in nsDisplayList.cpp will end up giving the layer the result from animations (and ignoring the one from transitions).

https://hg.mozilla.org/users/dbaron_mozilla.com/patches/raw-file/1b19c4c230a0/separate-generation-counters is a shot at what we'd need to do to fix this, although the patch needs a little cleanup.  I'm a little hesitant to touch this code given its current testing situation (bug 788549), though.

Comment 1

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Fixed by bug 1229280.