#define LEFT_EDGE 0x1 #define RIGHT_EDGE 0x2 #define BOTTOM_EDGE 0x4 #define TOP_EDGE 0x8 #define INSIDE(a) (!a) #define REJECT(a,b) (a&b) #define ACCEPT(a,b) (!(a|b)) #define FALSE 0 #define TRUE 1 struct point2d { int x; int y; }; unsigned char encode(struct point2d pt,struct point2d winMin,struct point2d winMax) { unsigned char code=0x00; if(pt.xwinMax.x) code = code | RIGHT_EDGE; if(pt.ywinMax.y) code = code | TOP_EDGE; return code; } void swapPts(struct point2d *p1,struct point2d *p2) { struct point2d tmp; tmp=*p1; *p1=*p2; *p2=tmp; } void swapCodes(unsigned char *c1,unsigned char * c2) { unsigned char tmp; 

tmp=*c1; *c1=*c2; *c2=tmp; } void clipLine(struct point2d winMin,struct point2d winMax,struct point2d p1,struct point2d p2) { unsigned char code1,code2; int done=FALSE,draw=FALSE; float m; while(!done) { code1=encode(p1,winMin,winMax); code2=encode(p2,winMin,winMax); if(ACCEPT(code1,code2)) { done=TRUE; draw=TRUE; } else { if(REJECT(code1,code2)) { done=TRUE; } else { if(INSIDE(code1)) { swapPts(&p1,&p2); swapCodes(&code1,&code2); } if(p2.x!=p1.x) m=(float)(p2.y-p1.y)/(p2.x-p1.x); if(code1 & LEFT_EDGE) { p1.y+=(winMin.x-p1.x)*m; p1.x=winMin.x; } else { if(code1 & RIGHT_EDGE) { 

p1.y+=(winMax.x-p1.x)*m; p1.x=winMax.x; } else { if(code1 & BOTTOM_EDGE) { if(p2.x!=p1.x) p1.x+=(winMin.y-p1.y)/m; p1.y=winMin.y; } else { if(code1 & TOP_EDGE) { if(p2.x!=p1.x) p1.x+=(winMax.y-p1.y)/m; p1.y=winMax.y; } } } } } } } if(draw) line(p1.x,p1.y,p2.x,p2.y); }