zfunction(3G)							 zfunction(3G)

NAME    [Toc]    [Back]

     zfunction - specifies the function	used for z-buffer comparison by	the
     current framebuffer

C SPECIFICATION    [Toc]    [Back]

     void zfunction(func)
     long func;

PARAMETERS    [Toc]    [Back]

     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	zbuffer
 bitplanes.

	    ZF_ALWAYS, the z-buffer function always passes.

DESCRIPTION    [Toc]    [Back]

     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    [Toc]    [Back]

     drawmode, zbuffer,	zsource

NOTES    [Toc]    [Back]

     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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