writemask(3G)

NAME
     writemask - grants write permission to bitplanes

C SPECIFICATION
     void writemask(wtm)
     Colorindex wtm;

PARAMETERS
     wtm   expects a mask whose bits control which bitplanes are available for
           drawing and which are read only.

           The mask contains one bit per available bitplane. If a bit is set
           in the writemask, the system writes the current color index into
           the corresponding bitplane. If a bit is set to zero in the
           writemask, the corresponding bitplane is read-only.

DESCRIPTION
     Use writemask to reserve bitplanes for special purposes.  When the
     writemask marks a bitplane as read-only, that bitplane is write protected
     from ordinary drawing routines.

     Use RGBwritemask in RGB mode.

SEE ALSO
     color, drawmode, RGBwritemask

BUGS
     writemask does not work properly on the IRIS-4D VGX, VGXT and SKYWRITER
     models when the current drawmode is not NORMALDRAW.