zbuffer

[David A. Tristram]

There doesn;t seem to be much in the way of documentation for z-buffer
access for 3000 or 4d/60's, however, if its any consolation, the GT
has *extensive* access to the z-buffer, including read/write and 
control of the comparison mode (ALWAYS,<,==,>,<=,>=,!=,NEVER), primitive
writemasks (on or off, basically), and when drawing, z-type comparisons
may also be made from the regular image planes.  How's that for the old
'its fixed in the next version' frustrations?

tristram