The scrmask subroutine defines a rectangular, two-dimensional clipping mask. It is intended to be used primarily for fine character clipping, although it clips all drawing primitives, including clear . By default, the viewport subroutine sets the same area for both the viewport and screenmask , which the parameters left , right , bottom , top define. All drawing routines are also clipped to the viewport, but the scrmask subroutine is useful only for characters.
Gross clipping is sufficient for all other primitives.
Parameters left Specifies the coordinate of the left clipping plane of the screenmask. Specifies the coordinate of the right clipping plane of the screenmask. The left parameter must not be greater than the right parameter, nor the bottom parameter greater than the top parameter, otherwise no text can appear on the screen. The example C language program prompt.c uses the scrmask subroutine to define a new screenmask. Related Information Returning the current screenmask with the getscrmask subroutine.