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:

            ZF_NEVER, the z-buffer function never passes.

            ZF_LESS, the z-buffer function passes if the incoming pixel z
            value is less than the z value stored in the z-buffer bitplanes.

            ZF_EQUAL, the z-buffer function passes if the incoming pixel z
            value is equal to the z value stored in the z-buffer bitplanes.

            ZF_LEQUAL, 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.)

            ZF_GREATER, the z-buffer function passes if the incoming pixel z
            value is greater than the z value stored in the z-buffer
            bitplanes.

            ZF_NOTEQUAL, the z-buffer function passes if the incoming pixel z
            value is not equal to the z value stored in the z-buffer
            bitplanes.

            ZF_GEQUAL, 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.

            ZF_ALWAYS, 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.
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.