zfunction(3G) zfunction(3G)
NAME
zfunction - specifies the function used for z-buffer comparison by the
current framebuffer
C SPECIFICATION
void zfunction(func)
long func;
PARAMETERS
func expects one of eight possible flags used when comparing z values.
The available flags are:
ZFNEVER, the z-buffer function never passes.
ZFLESS, the z-buffer function passes if the incoming pixel z
value is less than the z value stored in the z-buffer bitplanes.
ZFEQUAL, the z-buffer function passes if the incoming pixel z
value is equal to the z value stored in the z-buffer bitplanes.
ZFLEQUAL, the z-buffer function passes if the incoming pixel z
value is less than or equal to the z value stored in the z-buffer
bitplanes. (This is the default value.)
ZFGREATER, the z-buffer function passes if the incoming pixel z
value is greater than the z value stored in the z-buffer
bitplanes.
ZFNOTEQUAL, the z-buffer function passes if the incoming pixel z
value is not equal to the z value stored in the z-buffer
bitplanes.
ZFGEQUAL, the z-buffer function passes if the incoming pixel z
value is greater than or equal to the z value stored in the z-
buffer bitplanes.
ZFALWAYS, the z-buffer function always passes.
DESCRIPTION
zfunction specifies the function used to compare each incoming pixel z
value with the z value present in the z-buffer bitplanes. For example,
if func is ZF_LESS and the incoming pixel z value is less than the z
value in the z-buffer bitplanes, the comparison passes. Refer to the
zbuffer manual page for an explanation of z-buffer operation in the cases
of z function pass and failure.
A separate zfunction mode is retained by each of the framebuffers:
normal, popup, overlay, and underlay. The current draw mode determines
which z function value is used, and which is modified by zfunction.
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zfunction(3G) zfunction(3G)
SEE ALSO
drawmode, zbuffer, zsource
NOTES
Currently z-buffer operation is supported only in the normal framebuffer.
To insure compatibility with future releases of the GL, make calls to
zfunction only while draw mode is NORMALDRAW.
On the Personal Iris, if you use zfunction with czclear you can increase
the speed of buffer clearing.
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