scrmask(3G) scrmask(3G)
NAME
scrmask - defines a rectangular screen clipping mask
C SPECIFICATION
void scrmask(left, right, bottom, top)
Screencoord 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
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
drawmode, getscrmask, viewport
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.
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