zbuffe(3G)zbuffe(3G)NAMEzbuffe - enable or disable z-buffer operation in the current framebuffer
FORTRAN 77 SPECIFICATION
subroutine zbuffe(bool)
logical bool
PARAMETERS
bool is either .TRUE. or .FALSE..
.TRUE. enables z-buffer operation.
.FALSE. disables z-buffer operation.
DESCRIPTIONzbuffe turns z-buffer mode off or on for the current framebuffer, one of
normal, popup, overlay, and underlay, as specified by drawmo. 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 zfunct.
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
drawmo, getzbu, lsetde, stenci, zclear, zdraw, zfunct, zsourc, zwrite
NOTE
On some models z-buffer hardware is optional. Call getgde(GDBNZB) 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
zbuffe only while draw mode is NORMAL.
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.
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zbuffe(3G)zbuffe(3G)
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 PUPDRA,
OVERDR, and UNDERD. This operation is incorrect and will be changed in a
future release of the Graphics Library.
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