Returns a real number indicating the fractional change in the scrollbar
setting that corresponds to a given change in thumb position. For
example, if the scrollbar is horizontal, the result indicates how much
the scrollbar setting must change to move the thumb deltaX pixels to the
right (deltaY is ignored in this case). If the scrollbar is vertical,
the result indicates how much the scrollbar setting must change to move
the thumb deltaY pixels down. The arguments and the result may be zero
or negative.
Returns a real number indicating the fractional change in the scrollbar setting that corresponds to a given change in thumb position. For example, if the scrollbar is horizontal, the result indicates how much the scrollbar setting must change to move the thumb deltaX pixels to the right (deltaY is ignored in this case). If the scrollbar is vertical, the result indicates how much the scrollbar setting must change to move the thumb deltaY pixels down. The arguments and the result may be zero or negative.