reset method
Restore the effect to its original state as it was when the effect was just created.
A common use case for this method is to have an effect which is
permanently attached to its target (i.e. with removeOnFinish == false
),
and then periodically resetting this effect each time you need to apply
it to the target.
Implementation
@override
void reset() {
super.reset();
// We can't accumulate rounding errors between resets because we don't know
// if the opacity has been affected by anything else in between.
_roundingError = 0.0;
}