scrmas(3G)

NAME
     scrmas - defines a rectangular screen clipping mask

FORTRAN 77 SPECIFICATION
     subroutine scrmas(left, right, bottom, top)
     integer*4 left, right, bottom, top

PARAMETERS
     left     expects the window coordinate of the left-most pixel column
              within the mask region.

     right    expects the window coordinate of the right-most pixel column
              within the mask region.

     bottom   expects the window coordinate of the lowest pixel row within the
              mask region.

     top      expects the window coordinate of the highest pixel row within
              the mask region.

DESCRIPTION
     scrmas defines a subregion of the current viewport that can be updated by
     drawing commands.  Pixels outside this region cannot be modified by any
     drawing commands, including point, line, polygon, character, pixel write,
     and pixel copy commands.  All pixel bitplane buffers, including color,
     depth, accumulation, and stencil buffers, are write protected.  scrmas
     operates in all draw modes.

     The enabled subregion is specified as a screen-aligned rectangle in
     window coordinates.  Like viewpo, the boundary specification is
     inclusive, so the call scrmas(0,0,0,0) specifies a 1-pixel rectangle in
     the lower-left corner of the window.

     When viewpo is called, the screen mask is set to match the newly
     specified viewport.  Any previous scrmas specification is lost.

     scrmas must be specified entirely within the current viewport.

SEE ALSO
     drawmo, getscr, viewpo

NOTE
     If you set left to be greater than right or bottom to be greater than
     top, all pixels in the viewport are write protected.