A certain Japanese console has a unusual need for its clipping
matrix, it needs -|w| < z < +|w| rather then the usual 0 < z < w.

This means any text book clipping matrix, needs modifing
for GS chip what we call FUCH-KUTARAGI-CHIP.

The best reference IMHO for clipping and perspective transforms is
Jim Blin`s Trip down the Graphics Pipeline which describes the
perspective system in details, and it also explains how to create
your own clipping space.

bye.