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Assembly Source File | 1993-12-27 | 14.9 KB | 756 lines

TITLE XYCLIP - SUTHERLAND-HODGEMAN CLIPPER IN ASSEMBLER COMMENT $ // 26/12/93 by Dave Stampe // All algorithms and code (c) 1993 by Dave Stampe /* This code is part of the REND386 project, created by Dave Stampe and Bernie Roehl. Copyright 1992, 1993, 1994 by Dave Stampe and Bernie Roehl. May be freely used to write software for release into the public domain; all commercial endeavours MUST contact BOTH Bernie Roehl and Dave Stampe for permission to incorporate any part of this software into their products! Usually there is no charge for under 50-100 items for low-cost or shareware, and terms are reasonable. Any royalties are used for development, so equipment is often acceptable payment. ATTRIBUTION: If you use any part of this source code or the libraries in your projects, you must give attribution to REND386, Dave Stampe, and Bernie Roehl in your documentation, source code, and at startup of your program. Let's keep the freeware ball rolling! No more code ripoffs please. CONTACTS: dstampe@psych.toronto.edu, broehl@sunee.uwaterloo.ca See the COPYRITE.H file for more information. */ This is a reasonably efficient semi-recursive XY screen clipper for polygons. XY_clip_array() is the C call, which takes an array of (NVERTEX *) and processes to an output array. New clipped vertices may be produced: old vertices are not discarded. /* Contact: dstampe@sunee.waterloo.edu */ $ .MODEL large .386 .DATA include 3dstruct.inc include viewdata.inc ; clipper record variables first_top_vtx dd 0 ; for each level: record first, and latest vertex last_top_vtx dd 0 first_bottom_vtx dd 0 last_bottom_vtx dd 0 first_left_vtx dd 0 last_left_vtx dd 0 first_right_vtx dd 0 last_right_vtx dd 0 destptr dd 0 ; where to put output vtxcount dw 0 ; vertex passed count include rendmem.inc .CODE RENDERER ; defined in RENDMEM.INC ; alloc new vertex ; returns new vertex in ES:BX ; BX only affected ;ALLOCVTX MACRO ; les bx,_nvalloc ; sub bx, SIZE NVERTEX ; mov _nvalloc,bx ; mov WORD PTR es:[bx].NV_persp,0 ; ENDM ;/********** CREATE NEW INTERCEPT VERTEX **************/ ; static NVERTEX *y_intercept(NVERTEX *v1, NVERTEX *v2, long edge) ; static NVERTEX *x_intercept(NVERTEX *v1, NVERTEX *v2, long edge) ; ARGUMENTS: ; v1: ES:SI ; v2: ES:DI ; edge: ecx ; new, return: ES:BX ; MAKES ASSUMPTION THAT ALL x1 equ DWORD PTR es:[di].NV_xs ; NVERTEX ARE IN SAME SEGMENT y1 equ DWORD PTR es:[di].NV_ys z1 equ DWORD PTR es:[di].NV_z ; vtx 1 x2 equ DWORD PTR es:[si].NV_xs ; vtx 2 y2 equ DWORD PTR es:[si].NV_ys z2 equ DWORD PTR es:[si].NV_z xn equ DWORD PTR es:[bx].NV_xs ; intercept yn equ DWORD PTR es:[bx].NV_ys zn equ DWORD PTR es:[bx].NV_z y_intercept proc near ALLOCVTX ; es:bx is new vertex, assume es is renderer temp mov yn,ecx mov ecx,y1 sub ecx,y2 jl fwd_clip_y ; clip from high end to prevent roundoff jg rev_clip_y mov eax,x1 ; no slope: copy vtx 1 mov xn,eax mov eax,z1 mov zn,eax ret rev_clip_y: mov eax,yn ; compute new z sub eax,y2 mov edx,z1 sub edx,z2 imul edx idiv ecx add eax,z2 mov zn,eax mov eax,yn ; compute new x sub eax,y2 mov edx,x1 sub edx,x2 imul edx idiv ecx add eax,x2 mov xn,eax ret fwd_clip_y: neg ecx mov eax,yn ; compute new z sub eax,y1 mov edx,z2 sub edx,z1 imul edx idiv ecx add eax,z1 mov zn,eax mov eax,yn ; compute new x sub eax,y1 mov edx,x2 sub edx,x1 imul edx idiv ecx add eax,x1 mov xn,eax ret y_intercept endp x_intercept proc near ALLOCVTX ; es:bx is new vertex, assume es is renderer temp mov xn,ecx mov ecx,x1 sub ecx,x2 jl fwd_clip_x ; clip from high end to prevent roundoff jg rev_clip_x mov eax,y1 ; no slope: copy vtx 1 mov yn,eax mov eax,z1 mov zn,eax ret rev_clip_x: mov eax,xn ; compute new z sub eax,x2 mov edx,z1 sub edx,z2 imul edx idiv ecx add eax,z2 mov zn,eax mov eax,xn ; compute new y sub eax,x2 mov edx,y1 sub edx,y2 imul edx idiv ecx add eax,y2 mov yn,eax ret fwd_clip_x: neg ecx mov eax,xn ; compute new z sub eax,x1 mov edx,z2 sub edx,z1 imul edx idiv ecx add eax,z1 mov zn,eax mov eax,xn ; compute new y sub eax,x1 mov edx,y2 sub edx,y1 imul edx idiv ecx add eax,y1 mov yn,eax ret x_intercept endp ;/************* CLIPPER C INTERFACE **********/ ; XY clip an array of vertices, store in array ; returns number of vertices produced ; ; int XY_clip_array(NVERTEX **src, NVERTEX **dest, int count); src equ DWORD PTR [bp+8] ; arguments dest equ DWORD PTR [bp+12] count equ WORD PTR [bp+16] srcptr equ DWORD PTR [bp-4] ; locals n equ WORD PTR [bp-8] ; vertex counter ;CHECKMEM MACRO num_vertex ;; DEFINED IN RENDMEM.INC ; mov ax,num_vertex ; imul ax,SIZE NVERTEX ; add ax,200 ; add ax,WORD PTR _npalloc ; neg ax ; add ax,WORD PTR _nvalloc ; carry clear if out of memory ; ENDM PUBLIC _XY_clip_array _XY_clip_array proc far push ebp mov ebp,esp sub esp,16 push esi push edi push ecx push edx mov last_top_vtx,0 ; reset clipper variables mov last_bottom_vtx,0 mov last_left_vtx,0 mov last_right_vtx,0 mov vtxcount,0 mov eax,src mov srcptr,eax mov eax,dest mov destptr,eax mov ax,count mov n,ax ; enough mem for all vtxs? CHECKMEM 10 jc have_memory mov vtxcount,-1 jmp exit_clip have_memory: next_clip: mov ax,OTOP ; call top level of clipper push ax les bx,srcptr mov eax,es:[bx] push eax call near ptr XY_clip add esp,6 add srcptr,4 dec n jne next_clip cmp count,2 jle exit_clip mov ax,OTOP ; flush clipper push ax xor eax,eax push eax call near ptr XY_clip add esp,6 exit_clip: mov ax,vtxcount pop edx pop ecx pop edi pop esi mov esp,ebp pop ebp ret _XY_clip_array endp ;/************ RECURSIVE CLIPPER KERNAL *************/ ;static void XY_clip(NVERTEX *vtx, int stage) ; /* XY semirecursive clipper */ ; /* set last = NULL before first call */ ; /* call with all (copied) vertices */ ; /* call with NULL to flush */ ; /* also copies output to poly table */ vtx equ DWORD PTR [bp+6] ; arguments stage equ WORD PTR [bp+10] ; FOR NEAR CALL OFFSETS XY_clip proc near push ebp ; generic entry mov ebp,esp mov ax,stage ; find stage cmp ax,OTOP je top_clip cmp ax,ORIGHT je right_clip cmp ax,OBOTTOM je bottom_clip jmp left_clip XY_clip_bottom: ; fast local entries push ebp mov ebp,esp jmp bottom_clip XY_clip_left: push ebp mov ebp,esp jmp left_clip XY_clip_right: push ebp mov ebp,esp jmp right_clip XY_clip_top: push ebp mov ebp,esp ;;;;;;;; START OF TOP CLIP;;;;;;;;;;; top_clip: mov eax,DWORD PTR last_top_vtx ; is this the first? or eax,eax jnz not_first_top or eax,vtx ; traps NULL if first=last je right_clip mov last_top_vtx,eax ; record mov first_top_vtx,eax les bx,vtx mov al,BYTE PTR es:[bx].NV_ocode ; pass if in window test al,OTOP ; we can use outcode on first only jnz end_XY_clip jmp right_clip not_first_top: ; OK, we've got an edge mov eax,DWORD PTR vtx or eax,eax jnz not_flush_top ; NULL to flush clipper les si,first_top_vtx ; look for window top crossing mov al,BYTE PTR es:[si].NV_ocode les di,last_top_vtx xor al,BYTE PTR es:[di].NV_ocode test al,OTOP jz right_clip ; nv = y_intercept(first_top_vtx, last_top_vtx, VS_top4); ; XY_clip(nv,RIGHT); /* process this new point */ mov ecx,_VS_top4 ; si,di,es already loaded call y_intercept ; create intercept vertex push es push bx call near ptr XY_clip_right ; and clip it add esp,4 jmp right_clip ; continue to flush not_flush_top: les si,vtx mov al,BYTE PTR es:[si].NV_ocode push ax les di,last_top_vtx xor al,BYTE PTR es:[di].NV_ocode test al,OTOP jz do_top_clip mov ecx,_VS_top4 ; si,di,es already loaded call y_intercept ; create intercept vertex push es push bx ; and clip it call near ptr XY_clip_right add esp,4 ; continue with original vertex do_top_clip: mov eax,vtx ; ave as last vertex mov last_top_vtx,eax pop ax test al,OTOP ; was vertex in window? jnz end_XY_clip ; no: discard it ;;;;;;;; START OF RIGHT CLIP;;;;;;;;;;; right_clip: mov eax, last_right_vtx or eax,eax jnz not_first_right or eax, vtx je bottom_clip mov last_right_vtx,eax ; first vertex mov first_right_vtx,eax les bx, vtx mov eax, es:[bx].NV_xs cmp eax, _VS_right4 jg end_XY_clip jmp bottom_clip not_first_right: mov eax, vtx or eax,eax jnz not_flush_right les si, first_right_vtx ; flush: test for in-out pair mov eax, es:[si].NV_xs cmp eax, _VS_right4 jle pas1b les di, last_right_vtx mov eax, es:[di].NV_xs cmp eax, _VS_right4 jle pas2b jmp bottom_clip pas1b: les di, last_right_vtx mov eax, es:[di].NV_xs cmp eax, _VS_right4 jg pas2b jmp bottom_clip pas2b: ; nv = x_intercept(first_right_vtx, last_right_vtx, VS_right4); ; XY_clip(nv,BOTTOM); /* process this new point */ mov ecx,_VS_right4 ; si,di,es already loaded call x_intercept ; create intercept vertex push es push bx call near ptr XY_clip_bottom ; and clip it add esp,4 jmp bottom_clip ; continue to flush not_flush_right: ; full in-out test les si, vtx mov eax, es:[si].NV_xs cmp eax, _VS_right4 jle pat1b les di, last_right_vtx mov eax, es:[di].NV_xs cmp eax, _VS_right4 jg no_right_clip ; nv = x_intercept(vtx, last_right_vtx, VS_right4); ; XY_clip(nv,BOTTOM); /* process this new point */ mov ecx,_VS_right4 ; si,di,es already loaded call x_intercept ; create intercept vertex push es push bx call near ptr XY_clip_bottom ; and clip it add esp,4 no_right_clip: mov eax, vtx ; save mov last_right_vtx,eax ; was outside, so junk vtx jmp end_XY_clip pat1b: ; in-window test cont'd les di, last_right_vtx mov eax, es:[di].NV_xs cmp eax, _VS_right4 jle do_right_clip ; nv = x_intercept(vtx, last_right_vtx, VS_right4); ; XY_clip(nv,BOTTOM); /* process this new point */ mov ecx,_VS_right4 ; si,di,es already loaded call x_intercept ; create intercept vertex push es push bx call near ptr XY_clip_bottom ; and clip it add esp,4 do_right_clip: mov eax, vtx ; was in window: continue mov last_right_vtx,eax ;;;;;;;; START OF BOTTOM CLIP;;;;;;;;;;; bottom_clip: mov eax, last_bottom_vtx or eax,eax jnz not_first_bottom or eax, vtx je left_clip mov last_bottom_vtx,eax mov first_bottom_vtx,eax les bx, vtx mov eax, es:[bx].NV_ys cmp eax, _VS_bottom4 jg end_XY_clip jmp left_clip not_first_bottom: mov eax, vtx or eax,eax jnz not_flush_bottom les si, first_bottom_vtx mov eax, es:[si].NV_ys cmp eax, _VS_bottom4 jle pas1bb les di, last_bottom_vtx mov eax, es:[di].NV_ys cmp eax, _VS_bottom4 jle pas2bb jmp left_clip pas1bb: les di, last_bottom_vtx mov eax, es:[di].NV_ys cmp eax, _VS_bottom4 jg pas2bb jmp left_clip pas2bb: ; nv = y_intercept(first_bottom_vtx, last_bottom_vtx, VS_bottom4); ; XY_clip(nv,LEFT); /* process this new point */ mov ecx,_VS_bottom4 ; si,di,es already loaded call y_intercept ; create intercept vertex push es push bx call near ptr XY_clip_left ; and clip it add esp,4 jmp left_clip ; continue flush not_flush_bottom: les si, vtx mov eax, es:[si].NV_ys cmp eax, _VS_bottom4 jle pat1t les di, last_bottom_vtx mov eax, es:[di].NV_ys cmp eax, _VS_bottom4 jg no_bottom_clip ; nv = y_intercept(vtx, last_bottom_vtx, VS_bottom4); ; XY_clip(nv,LEFT); /* process this new point */ mov ecx,_VS_bottom4 ; si,di,es already loaded call y_intercept ; create intercept vertex push es push bx call near ptr XY_clip_left ; and clip it add esp,4 no_bottom_clip: mov eax, vtx mov last_bottom_vtx,eax jmp end_XY_clip ; out, so discard it pat1t: les di, last_bottom_vtx mov eax, es:[di].NV_ys cmp eax, _VS_bottom4 jle do_bottom_clip ; nv = y_intercept(vtx, last_bottom_vtx, VS_bottom4); ; XY_clip(nv,LEFT); /* process this new point */ mov ecx,_VS_bottom4 ; si,di,es already loaded call y_intercept ; create intercept vertex push es push bx call near ptr XY_clip_left ; and clip it add esp,4 ; in, so continue do_bottom_clip: mov eax, vtx mov last_bottom_vtx,eax ;;;;;;;; START OF LEFT CLIP;;;;;;;;;;; left_clip: mov eax, last_left_vtx or eax,eax jnz not_first_left or eax, vtx je end_XY_clip mov last_left_vtx,eax mov first_left_vtx,eax les bx, vtx mov eax, es:[bx].NV_xs cmp eax, _VS_left4 jl end_XY_clip jmp do_left_clip not_first_left: mov eax, vtx or eax,eax jnz not_flush_left les si, first_left_vtx mov eax, es:[si].NV_xs cmp eax, _VS_left4 jge pas1x les di, last_left_vtx mov eax, es:[di].NV_xs cmp eax, _VS_left4 jge pas2x jmp end_XY_clip pas1x: les di, last_left_vtx mov eax, es:[di].NV_xs cmp eax, _VS_left4 jge end_XY_clip pas2x: ; nv = x_intercept(first_left_vtx, last_left_vtx, VS_left4); mov ecx,_VS_left4 ; si,di,es already loaded call x_intercept ; create intercept vertex mov ax,es ; build far ptr shl eax,16 mov ax,bx les di,destptr add destptr,4 mov es:[di],eax ; store new vertex ptr inc vtxcount jmp end_XY_clip not_flush_left: les si, vtx mov eax, es:[si].NV_xs cmp eax, _VS_left4 jge pat1x les di, last_left_vtx mov eax, es:[di].NV_xs cmp eax, _VS_left4 jl no_left_clip ; nv = x_intercept(vtx, last_left_vtx, VS_left4); mov ecx,_VS_left4 ; si,di,es already loaded call x_intercept ; create intercept vertex mov ax,es ; build far ptr shl eax,16 mov ax,bx les di,destptr add destptr,4 mov es:[di],eax ; store new vertex ptr inc vtxcount no_left_clip: mov eax, vtx mov last_left_vtx,eax jmp end_XY_clip pat1x: les di, last_left_vtx mov eax, es:[di].NV_xs cmp eax, _VS_left4 jge do_left_clip ; nv = x_intercept(vtx, last_left_vtx, VS_left4); mov ecx,_VS_left4 ; si,di,es already loaded call x_intercept ; create intercept vertex mov ax,es ; build far ptr shl eax,16 mov ax,bx les di,destptr add destptr,4 mov es:[di],eax ; store new vertex ptr inc vtxcount do_left_clip: mov eax, vtx mov last_left_vtx,eax les di,destptr add destptr,4 mov es:[di],eax ; store new vertex ptr inc vtxcount end_XY_clip: mov esp,ebp pop ebp ret XY_clip endp end