zwrite(3G)

NAME
     zwrite - specifies a write mask for the z-buffer of the current
     framebuffer

FORTRAN 77 SPECIFICATION
     zwrite(mask)
     integer*4 mask;

PARAMETERS
     mask   expects a mask indicating which z-buffer bitplanes are read only
            and which can be written to.  Z-buffer bitplanes that correspond
            to zeros in the mask are read only.  Z-buffer bitplanes that
            correspond to ones in the mask can be written.

DESCRIPTION
     zwrite specifies a mask used to control which z-buffer bitplanes are
     written, and which are read only.  A separate mask is maintained by each
     of the framebuffers, normal, popup, overlay, and underlay.  The mask
     affects both writes to the z-buffer that are the result of z-buffer pixel
     operation, and writes resulting from zclear operation.

     zwrite is ignored while drawing directly to the z-buffer, as when zdraw
     is TRUE. In this case the current writemask applies to the z-buffer as
     well as to the color bitplanes.

     zwrite is initialized when a window is created, and when gconfi is
     called, to enable all z-buffer bitplanes.

SEE ALSO
     gconfi, wmpack, writem, zbuffer, zdraw

NOTES
     Currently z-buffer operation is supported only in the normal framebuffer.
     To insure compatibility with future releases of the GL, make calls to
     zwrite only while draw mode is NORMAL.

BUGS
     This subroutine does not function on IRIS-4D B or G models.

     IRIS-4D GT and GTX models, RealityEngine models, and the Personal Iris,
     currently support a subset of z write mask functionality.  Specifically,
     zwrite either enables or disables the writing of all z-buffer bitplanes.
     The mask passed to zwrite will disable z-buffer writes if it is zero;
     otherwise all z-buffer bitplanes are written.  To assure upward
     compatibility with the IRIS-4D VGX and other future models, call zwrite
     with mask equal to either 0 or $FFFFFFFF when all-or-nothing update is
     desired.

     On Impact and Infinite Reality individual z bitplanes are not maskable.