zsource(3G)							   zsource(3G)

NAME    [Toc]    [Back]

     zsource - selects the source for z-buffering comparisons

C SPECIFICATION    [Toc]    [Back]

     void zsource(src)
     long src;

PARAMETERS    [Toc]    [Back]

     src   expects one of two possible values:

	   ZSRC_DEPTH, z-buffering is done by depth comparison (default).

	   ZSRC_COLOR, z-buffering is done by color comparison.

DESCRIPTION    [Toc]    [Back]

     By	default	z-buffer comparisons are done on depth data.  However, in
     certain cases, it can be useful to	z-buffer by comparing color values,
     especially	the color index	values generated by the	linesmooth and
     pntsmooth hardware.  When the src parameter is ZSRC_DEPTH,	the z-buffer
     operation is normal.  When	 the src parameter is ZSRC_COLOR, however,
     source and	destination color values are compared to determine which
     pixels the	system draws.  In this mode, the zbuffer is not	updated	when a
     pixel is written.

     A separate	zsource	mode is	retained by each of the	framebuffers:  normal,
     popup, overlay, and underlay.  The	current	draw mode determines which z
     source mode is used, and which is modified	by zsource.

SEE ALSO    [Toc]    [Back]

     drawmode, gversion, linesmooth, pntsmooth,	zbuffer, zfunction

NOTES    [Toc]    [Back]

     This subroutine does not function on IRIS-4D B or G models.

     Currently z-buffer	operation is supported only in the normal framebuffer.
     To	insure compatibility with future releases of the GL, make calls	to
     zsource only while	draw mode is NORMALDRAW.

     Use zsource(ZSRC_COLOR) for correct anti-aliasing support in color	index
     mode on Iris Indy and Iris	Indigo.

BUGS    [Toc]    [Back]

     IRIS-4D GT	and GTX	models support zsource(ZSRC_COLOR) only	for nonsubpixel
 positioned lines drawn after a linesmooth(SML_ON)	call.

     On	early serial numbers of	the Personal Iris, ZSRC_DEPTH is the only
     supported setting for this	routine. For compatibility, they accept	the
     call zsource(ZSRC_COLOR), but it has the same effect as calling
     zfunction(ZF_ALWAYS), which turns off z value comparison. This allows the
     unrestricted drawing of color values into the front and back buffers and
     depth values into the z-buffer.  Use gversion to determine	which type of
     Personal Iris you have.



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zsource(3G)							   zsource(3G)



     IRIS-4D VGX models	support	zsource(ZSRC_COLOR) only in color map mode.
     Stencil operation is undefined in this case.


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