Computes the parameters for a blit where the backing store image currently contains oldLoc in the upper left hand corner and we're scrolling to newLoc. The parameters are modified to return the values required for the blit.

Parameters:

dx		the horizontal delta
dy		the vertical delta
blitFrom		the Point we're blitting from
blitTo		the Point we're blitting to
blitSize		the Dimension of the area to blit
blitPaint		the area to blit

Returns:  true if the parameters are modified and we're ready to blit; false otherwise