Bug 21025 – CSS transition with duration=0 and delay=0 doesn't override ongoing transition

• Component: CSS
• Status: VERIFIED FIXED

[Kari Hiitola]

When setting -webkit-transition-duration and -webkit-transition-delay to zero and starting a new transition during another transition, the new transition doesn't override the ongoing one but instead is completed after the ongoing transition is finished.

In the supplied test page the moving text on the top (#bug) should move immediately back to the upper left corner after the 2s timeout (When the text changes). Changing the delay or duration in function "test_bug" to 1ms overcomes this as demonstrated on the bottom part (#ok).

There is an explicit test for the zero-zero condition in the source code (WebCore/page/animation/CompositeAnimation.cpp) , and removing the test makes the problem disappear with the test page. I'm not sure if there would be any side-effects, though. 

It's not apparent to me, why immediate and undelayed transforms should not override the ongoing transition. As I've understood it,  that wouldn't indicate an empty transition, as the code comments hint (// If this is an empty transition, skip it).

[Chris Marrin]

Created attachment 23925 [details]
LayoutTest file

[Chris Marrin]

Bug was as you suspected. But I had to add a bit of logic to make sure to not add a transition if the delay and duration were 0. To do so would, at least, fire an end transition event erroneously. I also added an optimization to avoid doing the property equality test if the duration and delay were 0.

[Darin Adler]

Comment on attachment 23925 [details]
LayoutTest file

This is just the layout test file, not the patch at all!

[Chris Marrin]

Created attachment 23928 [details]
Patch, including LayoutTest file

[Chris Marrin]

Comment on attachment 23928 [details]
Patch, including LayoutTest file

Sorry, grabbed the wrong file. I need a better naming scheme!

Comment on attachment 23928 [details]
Patch, including LayoutTest file

r=me

[Chris Marrin]

Sending        LayoutTests/ChangeLog
Adding         LayoutTests/transitions/interrupt-zero-duration-expected.txt
Adding         LayoutTests/transitions/interrupt-zero-duration.html
Sending        WebCore/ChangeLog
Sending        WebCore/page/animation/CompositeAnimation.cpp
Sending        WebCore/page/animation/KeyframeAnimation.h
Transmitting file data ......
Committed revision 37485.