Sets the values of automatic scrollbars. (This method has no effect on manual scrollbars.)
If either argument is #f, the scrollbar value is not changed in the corresponding direction.
The h-value and v-value arguments each specify a fraction of the scrollbar's movement. A 0.0 value sets the scrollbar to its left/top, while a 1.0 value sets the scrollbar to its right/bottom. A 0.5 value sets the scrollbar to its middle. In general, if the canvas's virtual size is v, its client size is c, and (> v c), then scrolling to p sets the view start to (floor (* p (- v c))).