zsource(3G)

NAME
     zsource - selects the source for z-buffering comparisons

C SPECIFICATION
     void zsource(src)
     long src;

PARAMETERS
     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
     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
     drawmode, gversion, linesmooth, pntsmooth, zbuffer, zfunction

NOTES
     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
     IRIS-4D GT and GTX models support zsource(ZSRC_COLOR) only for non-
     subpixel 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.
     IRIS-4D VGX models support zsource(ZSRC_COLOR) only in color map mode.
     Stencil operation is undefined in this case.