If progress is not NULL, the animation progress will be returned
there, 0.0 means the state is closest to being FALSE, while 1.0 means
it’s closest to being TRUE. This means transition animations will
run from 0 to 1 when state is being set to TRUE and from 1 to 0 when
it’s being set to FALSE.
Returns TRUE if there is a transition animation running for the current region (see Style.contextPushAnimatableRegion).
If progress is not NULL, the animation progress will be returned there, 0.0 means the state is closest to being FALSE, while 1.0 means it’s closest to being TRUE. This means transition animations will run from 0 to 1 when state is being set to TRUE and from 1 to 0 when it’s being set to FALSE.