; $$TABS=8 ; simple, dumb 3d polygon clipper. include 'demo.i' include '3d.i' xref point_coder,vertex,UnClippedPolygon DrawClippedPolygon:: ; ; input d0=orcodes,d1=andcodes ; (a0)=src poly (a1)=end poly ONTIMER 6 move.w #4,cliplim(a6) lea temp_polygon_buffer2(pc),a2 reclip: btst #CLIPB_TOP,d0 beq.s no_topclip lea intersect_top(pc),a3 moveq #CLIPB_TOP,d3 bsr ClipPlane tst.w d1 ; codes_and !=0? beq.s no_topclip reject_polygon: OFFTIMER 6 rts no_topclip: btst #CLIPB_BOT,d0 beq.s no_botclip lea intersect_bot(pc),a3 moveq #CLIPB_BOT,d3 bsr ClipPlane tst.w d1 bne.s reject_polygon no_botclip: btst #CLIPB_RIGHT,d0 beq.s no_rightclip lea intersect_right(pc),a3 moveq #CLIPB_RIGHT,d3 bsr.s ClipPlane tst.w d1 bne.s reject_polygon no_rightclip: btst #CLIPB_LEFT,d0 beq.s no_leftclip lea intersect_left(pc),a3 moveq #CLIPB_LEFT,d3 bsr.s ClipPlane tst.w d1 bne.s reject_polygon no_leftclip: tst.w d0 ; any codes set? beq.s project_polygon subq.w #1,cliplim(a6) bne.s reclip OFFTIMER 6 rts project_polygon: ; now, project it and move it to vertex ONTIMER 7 lea vertex(a6),a2 moveq #0,d0 project_loop: move.w (a0)+,d4 move.w (a0)+,d5 move.w (a0)+,d6 lea 2(a0),a0 ; codes muls #(DUNGEON_WINDOW_WIDTH/2),d4 divs d6,d4 add.w #DUNGEON_WINDOW_WIDTH/2,d4 swap d4 muls #(DUNGEON_WINDOW_HEIGHT/2),d5 divs d6,d5 add.w #DUNGEON_WINDOW_HEIGHT/2,d5 move.w d5,d4 move.l d4,(a2)+ addq #1,d0 move.l (a0)+,(a2)+ cmp.l a0,a1 bne.s project_loop OFFTIMER 7 bsr UnClippedPolygon rts ClipPlane:: ; ClipPlane - clip a polygon against a plane. ; input: a0=src poly a1=end poly a2=dest poly a3=clip routine d3=clip bit ; output: d0=or'd codes d1=anded codes ; a1=new end a0,a2 swapped ; polygon format is x y z c u1 u2 ; where u1 and u2 are additional parameters to be clipped ; one clipper instead of 4 for simplicity and to fit in cache. move.l a0,-(a7) move.l a2,-(a7) moveq #0,d0 ; orcodes=0 moveq #-1,d1 ; andcodes=-1. only lower word valid ; now, move first to last movem.l (a0),d2/d4/d5/d6/d7/a4 ; 6 lwords=2 pts movem.l d2/d4/d5/d6/d7/a4,(a1) lea 6*2(a1),a1 clip_loop: lea 6*2(a0),a0 ; skip initial point and handle in the wrap cmp.l a0,a1 beq.s done_clip trivial_accept_loop: move.w 6(a0),d6 ; fetch codes btst d3,d6 bne.s cur_off move.l (a0)+,(a2)+ ; x y or.w d6,d0 ; interleave writes and ops because of wait-states move.l (a0)+,(a2)+ ; z c and.w d6,d1 move.l (a0)+,(a2)+ ; u1 u2 cmp.l a0,a1 bne.s trivial_accept_loop done_clip: move.l a2,a1 ; a1=poly+npnts move.l (a7)+,a0 move.l (a7)+,a2 ; src and dest now swapped rts cur_off: ; the current point is off. ; if the previous was on, output the point bwteen prev and cur ; if the next is on, output the point between cur and next ; the plane clip routine takes d4/d5/d6=on point, (a5)=off point, d7=offy and returns ; d4/d5/d6=intxyz, d2=t btst d3,-12+7(a0) ; prv off? bne.s prv_was_off movem.w -12(a0),d4/d5/d6 move.l a0,a5 move.w 2(a5),d7 jsr (a3) ; call plane clip routine bsr point_coder movem.w d4-d7,(a2) ; output xyz or.w d7,d0 and.w d7,d1 lea 8(a2),a2 move.w 8(a0),d7 ; d7=u1 move.w -12+8(a0),d4 ; d4=u0 sub.w d4,d7 muls d2,d7 add.l d7,d7 swap d7 add.w d4,d7 move.w d7,(a2)+ move.w 10(a0),d7 ; d3=v1 move.w -12+10(a0),d4 ; d4=v0 sub.w d4,d7 muls d2,d7 add.l d7,d7 swap d7 add.w d4,d7 move.w d7,(a2)+ prv_was_off: btst d3,7+12(a0) ; next off? bne.s clip_loop ; next off too, so we are done movem.w 12(a0),d4/d5/d6 move.l a0,a5 move.w 2(a5),d7 jsr (a3) ; comput intersection bsr point_coder movem.w d4-d7,(a2) ; output xyz or.w d7,d0 and.w d7,d1 lea 8(a2),a2 move.w 8(a0),d7 ; d3=u1 move.w 12+8(a0),d4 ; d4=u0 sub.w d4,d7 muls d2,d7 add.l d7,d7 swap d7 add.w d4,d7 move.w d7,(a2)+ move.w 10(a0),d7 ; d3=v1 move.w 12+10(a0),d4 ; d4=v0 sub.w d4,d7 muls d2,d7 add.l d7,d7 swap d7 add.w d4,d7 move.w d7,(a2)+ bra clip_loop intersect_top: ; point is above z=y ; so, t=(z0-y0)/(y1-y0-z1+z0) ; out=(x1-x0)*t+x0,(y1-y0)*t+y0,y ; (a4)=x0 (a5)=x1 ; ret d4/d5/d6=xyz d2=t can trash d7/a4/a5 move.w d6,d2 ; d2=z0 sub.w d5,d2 ; d2=z0-y0 swap d2 clr.w d2 asr.l #1,d2 sub.w d5,d6 ; d6=z0-y0 add.w d7,d6 ; d6=y1-y0+z0 sub.w 4(a5),d6 ; d6=y1-y0-z1+z0 divs d6,d2 ; d2=t move.w d4,d6 ; d6=x0 sub.w (a5),d4 neg.w d4 ; d4=x1-x0 muls d2,d4 add.l d4,d4 swap d4 ; d4=t*(x1-x0) add.w d6,d4 ; d4=outx=t*(x1-x0)+x0 sub.w d5,d7 ; d7=y1-y0 muls d2,d7 add.l d7,d7 swap d7 add.w d7,d5 ; d5=outy=t*(x1-y0)+y0 move.w d5,d6 ; d6=outz=outy rts intersect_bot: ; point is below z=-y ; so, t=(z0+y0)/(y0+z0-z1-y1) ; out=(x1-x0)*t+x0,(y1-y0)*t+y0,-y ; (a4)=x0 (a5)=x1 ; ret d4/d5/d6=xyz d2=t can trash d7/a4/a5 move.w d6,d2 ; d2=z0 add.w d5,d2 ; d2=z0+y0 swap d2 clr.w d2 asr.l #1,d2 sub.w d7,d6 ; d6=z0-y1 add.w d5,d6 ; d6=z0-y1+y0 sub.w 4(a5),d6 ; d6=z0-y1+y0-z1 divs d6,d2 ; d2=t move.w d4,d6 ; d6=x0 sub.w (a5),d4 neg.w d4 ; d4=x1-x0 muls d2,d4 add.l d4,d4 swap d4 ; d4=t*(x1-x0) add.w d6,d4 ; d4=outx=t*(x1-x0)+x0 sub.w d5,d7 ; d7=y1-y0 muls d2,d7 add.l d7,d7 swap d7 add.w d7,d5 ; d5=outy=t*(x1-y0)+y0 move.w d5,d6 neg.w d6 ; d6=outz=-outy rts intersect_right: ; point is to the right of z=x ; so, t=(x0-z0)/(z1-x1+x0-z0) ; out=(x1-x0)*t+x0, (y1-y0)*t+y0, x move.w d4,d2 ; d2=x0 sub.w d6,d2 ; d2=x0-z0 swap d2 clr.w d2 asr.l #1,d2 neg.w d6 ; d6=-z0 add.w d4,d6 ; d6=x0-z0 sub.w (a5),d6 ; d6=-x1+x0-z0 add.w 4(a5),d6 ; d6=z1-x1+x0-z0 divs d6,d2 ; d2=t move.w d4,d6 ; d6=x0 sub.w (a5),d4 neg.w d4 ; d4=x1-x0 muls d2,d4 add.l d4,d4 swap d4 ; d4=t*(x1-x0) add.w d6,d4 ; d4=outx=t*(x1-x0)+x0 sub.w d5,d7 ; d7=y1-y0 muls d2,d7 add.l d7,d7 swap d7 add.w d7,d5 ; d5=outy=t*(y1-y0)+y0 move.w d4,d6 ; d6=outz=x rts intersect_left: ; point is to the left of z=-x ; so,t=(z0+x0)/(x0+z0-z1-x1) ; out=(x1-x0)*t+x0, (y1-y0)*t+y0, -x add d4,d6 ; d6=z0+x0 move d6,d2 swap d2 clr.w d2 asr.l #1,d2 sub.w (a5),d6 ; d6=z0+x0-x1 sub.w 4(a5),d6 ; d6=z0+x0-x1 divs d6,d2 ; d2=t move.w d4,d6 sub.w (a5),d4 ; x0-x1 neg.w d4 ; x1-x0 muls d2,d4 add.l d4,d4 swap d4 add.w d6,d4 ; d4=outx move.w d5,d6 ; d6=y0 sub.w d7,d5 ; y0-y1 neg.w d5 ; y1-y0 muls d2,d5 add.l d5,d5 swap d5 add.w d6,d5 move.w d4,d6 neg.w d6 rts temp_polygon_buffer2: ds.w 6*20 ; 18 vertices max section __MERGED,data cliplim:: dc.w 0