Scroll to a specific position.
scrollBy([in] int dx, [in] int dy)
This function is similar to
scrollTo, except that it scrolls relative to the current position. A positive
dxvalue scrolls right, a negative
dxvalue scrolls left. Similarly, positive and negative
dyvalues scroll down and up, respectively. For example:
viewer.scrollBy 5, -10would scroll 5 pixels to the right and 10 pixels up from the current position.