;
; now uses @def(symbol) command to check user additions...
;
; 11.October - start on planning for more efficient visibility
;              algorithm. Points are perspectivized, if z clip
;              OK a clipmask is calculated (else clipmask is negative)
;            - For calc_vis, *after* direction algorithm, clipmask
;              of poly is calculated and stored (instead of just
;              dot product)
;            - PLUS clipmask idea extended to write over z-coord,
;              done after perspective calculation. Z_clip is now
;              bit 4 of the clipmask (z clip calc by ORing masks
;              rather than ANDing to see if poly easily offscreen)
;              Storing instead of z-coord allows easy lookup
;              and saves memory!
;              >>>>>>BUT MUCKS UP THE Z-SORTING ALGORITHM>>>>>>
;			   Solution to this found, but "proper" z-clipping is out
;			   of the question
;	24.10.96	clipmask buffer set to shade_buffer+2 to allow
;				env/phong mapping
;
;	21.1.97		Work on gouraud-shaded texture-mapping
;				started
;	14.3.97		Environment-style texture-mapping
;
;	17.3.97		Bug introduced after fixing flat shading,
;			when sorted objects done
