RGBwritemask(3G)

NAME
     RGBwritemask - grants write access to a subset of available bitplanes

C SPECIFICATION
     void RGBwritemask(red, green, blue)
     short red, green, blue;

PARAMETERS
     red     expects the mask for the corresponding red bitplanes.

     green   expects the mask for the corresponding green bitplanes.

     blue    expects the mask for the corresponding blue bitplanes.

DESCRIPTION
     RGBwritemask sets the red, green, and blue write mask components of the
     currently active GL framebuffer, one of normal, popup, overlay, or
     underlay as specified by drawmode, to the specified values.  The alpha
     mask component is set to enable writing to all alpha bitplanes.  The
     current framebuffer must be in RGB mode for the RGBwritemask command to
     be applicable.  All drawing into the color bitplanes of the current
     framebuffer is masked by the current write mask.  Write mask components
     are retained in each draw mode, so when a draw mode is re-entered, the
     red, green, blue, and alpha masks are reset to the last values specified
     in that draw mode.

     Each write mask component is an 8-bit mask, which allows changes only to
     bitplanes corresponding to ones in the mask.  For example,
     RGBwritemask(0xF0,0x00,0x00) allows changes only to the 4 most
     significant bits of red, and to all the bits of alpha.  Bits 8 through 15
     of each component specification are ignored, only bits 0 through 7 are
     significant.

     It is an error to call RGBwritemask while the current framebuffer is in
     color map mode.

     The write mask components of all framebuffers in RGB mode are set to 0xFF
     when gconfig is called.

SEE ALSO
     drawmode, gRGBmask, RGBmode, wmpack

NOTE
     On Impact and Infinite Reality individual bits within a component cannot
     be masked.