Behavior of jumpTo

[Nir Lisker]

Hi,

As I'm continuing my work on the animations front, I came across an
ambiguous behavior of JumpTo. The specifications don't say anything about
it, but in FiniteClipEnvelop, if the rate is negative, it jumps to the
specified time *counted from the end*. This seems intentional because it's
checked explicitly:

                pos = ticks % cycleTicks;
                if (rate < 0) {
                    pos = cycleTicks - pos;
                }
                if ((pos == 0) && (ticks > 0)) {
                    pos = cycleTicks;
                }

SingleLoopClipEnvelope does not behave this way. I submitted [1] to track
this. This also causes an issue with jumping when rate=0, however, there
are other issues with rate=0, for example [2], and it's hard to separate
them.

What should be the proper behavior of jumpTo with respect to the rate? I
think that they shouldn't be coupled: jumping should always be calculated
from the start. The application can always calculate (totalTime -
requiredTime) and send that to jumpTo.

- Nir

[1] https://bugs.openjdk.java.net/browse/JDK-8237973
[2] https://bugs.openjdk.java.net/browse/JDK-8237757