Get the viewport canvas of a PtScrollArea
PhRect_t *PtScrollAreaCanvas( PtWidget_t *widget, PhRect_t *rect );
This function determines the canvas rectangle for the specified widget's viewport. The PtScrollArea canvas rectangle describes the area inside the widget's border; the viewport's canvas is the area inside the scrollbars. The rect argument must point to a PhRect_t structure; if you pass rect as NULL, the function returns NULL.
A pointer to the viewport's canvas, or NULL if an error occurs.
PhRect_t in the Photon Library Reference