RFR: 8236753: Animations do not play backwards after being stopped

[Ambarish Rapte]

On Fri, 10 Jan 2020 00:39:53 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> I'll review this next week. This seems a fine candidate for openjfx14, so it (along with a couple other pending reviews that can be for 14) will be a good test of targeting a PR to the stabilization branch.
>> 
>> I also request @arapte to review.
> 
> I should add that it will depend on whether there are any regressions. One thing we do need to be careful of is introducing regressions during rampdown.

The fix looks good to me.
After this change the steps needed for playing an `Animation` backwards will change.
Earlier this was documented with `Animation.play()` API as below.
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To play an `Animation` backwards from the end:
animation.setRate(negative rate);
animation.jumpTo(overall duration of animation);
animation.play();
-------------

After this PR call to `jumpTo()` won't be needed here.
So this PR may need a document change for `Animation.play()`.
Also to note that the behavior of above mentioned three calls remains same with the changes in this change.

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PR: https://git.openjdk.java.net/jfx/pull/82