zsourc(3G)

NAME
     zsourc - selects the source for z-buffering comparisons

FORTRAN 77 SPECIFICATION
     subroutine zsourc(src)
     integer*4 src

PARAMETERS
     src   expects one of two possible values:

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

           ZSRCCO, 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 ZSRCDE, the z-buffer
     operation is normal.  When  the src parameter is ZSRCCO, 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 zsourc 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 zsourc.

SEE ALSO
     drawmo, gversi, linesm, pntsmo, zbuffe, zfunct

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
     zsourc only while draw mode is NORMAL.

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

BUGS
     IRIS-4D GT and GTX models support zsourc(ZSRCCO) only for non-subpixel
     positioned lines drawn after a linesm(SMLON) call.

     On early serial numbers of the Personal Iris, ZSRCDE is the only
     supported setting for this routine. For compatibility, they accept the
     call zsourc(ZSCCCO), but it has the same effect as calling
     zfunct(ZFALWA), 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 gversi to determine which type of
     Personal Iris you have.
     IRIS-4D VGX models support zsourc(ZSRCCO) only in color map mode.
     Stencil operation is undefined in this case.