zbuffer(3G)

NAME
     zbuffer - enable or disable z-buffer operation in the current framebuffer

C SPECIFICATION
     void zbuffer(Boolean bool)

PARAMETERS
     bool   is either TRUE or FALSE.

            TRUE enables z-buffer operation.

            FALSE disables z-buffer operation.

DESCRIPTION
     zbuffer turns z-buffer mode off or on for the current framebuffer, one of
     normal, popup, overlay, and underlay, as specified by drawmode.  The z
     buffer is a bitplane bank that is associated with a single framebuffer,
     and that stores a depth value for each pixel in that framebuffer.  When
     z-buffer operation is enabled, the depth value associated with each
     incoming pixel is compared to the depth value stored in the framebuffer
     at that pixel location.  The comparison function is specified by
     zfunction.  If the comparison passes, the incoming pixel color is written
     into the color bitplane bank or banks, and the incoming pixel depth is
     written into the z-buffer bitplanes.  The current z write mask controls
     which z-buffer bitplanes are written with new depth data.

     If the comparison fails, no change is made to the contents of either the
     color bitplane banks or the z-buffer bitplane bank.  In some cases,
     however, a change is made to the contents of the stencil bitplanes.

     By default z-buffer operation is disabled in all framebuffers.

SEE ALSO
     drawmode, getzbuffer, lsetdepth, stencil, zclear, zdraw, zfunction,
     zsource, zwritemask

NOTE
     On some models z-buffer hardware is optional.  Call
     getgdesc(GD_BITS_NORM_ZBUFFER) to determine whether z-buffer hardware is
     available.

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

     Error accumulation in the iteration of z can cause wrapping when the full
     depth range supported by the graphics hardware is used.  (An iteration
     wraps when it accidentally converts a large positive value into a
     negative value, or vice versa.) While the effects of wrapping are
     typically not observed; if they are, they can be eliminated by reducing
     the depth range by a small percentage.
     At most four color buffers, such as front-left, front-right, back-left,
     back-right, and zdraw, can be rendered into simultaneously on the IRIS-4D
     RealityEngine model.

BUGS
     IRIS-4D GT and GTX models accept z-buffer commands, and support z-buffer
     operation using the normal z buffer, when the draw mode is PUPDRAW,
     OVERDRAW, and UNDERDRAW.  This operation is incorrect and will be changed
     in a future release of the Graphics Library.