The simple stepper decrements a start threshold with every update() call. It
is finished if the update value is not a number, below zero or larger than
the last value. It also stops if the decremented threshold falls below one.
Initialize the simple sequential stepper with a starting threshold.
threshold - The starting threshold.
public void update(double value)
Decrement the threshold if the stepper is not marked as finished.
Rendering a stepper finished happens if is not a number,
below or equal zero or bigger than the last update value. The same
thing happens if the internal threshold falls below one.