get-view-start in canvas%
Get the location at which the visible portion of the canvas starts,
based on the current values of the horizontal and vertical scrollbars
if they are initialized as automatic (see
init-auto-scrollbars ). Combined with
get-client-size, an application can efficiently redraw only the visible portion of
the canvas. The values are in pixels.
If the scrollbars are disabled or initialized as manual (see
init-manual-scrollbars), the result is 0.