zbuffer(3G)							   zbuffer(3G)

NAME    [Toc]    [Back]

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

C SPECIFICATION    [Toc]    [Back]

     void zbuffer(Boolean bool)

PARAMETERS    [Toc]    [Back]

     bool   is either TRUE or FALSE.

	    TRUE enables z-buffer operation.

	    FALSE disables z-buffer operation.

DESCRIPTION    [Toc]    [Back]

     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    [Toc]    [Back]

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

NOTE    [Toc]    [Back]

     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.




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zbuffer(3G)							   zbuffer(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    [Toc]    [Back]

     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.


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