scrmask(3G)							   scrmask(3G)

NAME    [Toc]    [Back]

     scrmask - defines a rectangular screen clipping mask

C SPECIFICATION    [Toc]    [Back]

     void scrmask(left,	right, bottom, top)
     Screencoord left, right, bottom, top;

PARAMETERS    [Toc]    [Back]

     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    [Toc]    [Back]

     scrmask 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.
     scrmask operates in all draw modes.

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

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

     scrmask must be specified entirely	within the current viewport.

SEE ALSO    [Toc]    [Back]

     drawmode, getscrmask, viewport

NOTE    [Toc]    [Back]

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


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