计算机图形学-裁减算法

1、Cohen-Sutherland裁减算法#define LEFT 1#define RIGHT 2#define BOTTOM 4#define TOP 8int encode(float x,float y) int c=0; if(xXR) c|=RIGHT; if(xYB) c|=BOTTOM; if(xYT) c|=TOP; retrun c;void CS_LineClip(x1,y1,x2,y2,XL,XR,YB,YT)float x1,y1,x2,y2,XL,XR,YB,YT;/(x1,y1)(x2,y2)为线段的端点坐标，其他四个参数定义窗口的边界 int code1,code

2、2,code; code1=encode(x1,y1); code2=encode(x2,y2); while(code1!=0 |code2!=0) /都为0,在窗口内,则取,直接绘制此直线. if(code1&code2 !=0) return; /与运算不为0,在窗口外,则弃, 不需处理 code = code1; if(code1=0) code = code2; /选择窗口外的端点 if(LEFT&code !=0) /该位编码不为0,与对应窗口边界求交 x=XL; y=y1+(y2-y1)*(XL-x1)/(x2-x1); else if(RIGHT&code !=0) x=XR;

3、 y=y1+(y2-y1)*(XR-x1)/(x2-x1); else if(BOTTOM&code !=0) y=YB;x=x1+(x2-x1)*(YB-y1)/(y2-y1);else if(TOP & code !=0) y=YT; x=x1+(x2-x1)*(YT-y1)/(y2-y1); if(code =code1) /用交点替换窗口外的端点,继续处理余下的线段. x1=x;y1=y; code1 =encode(x,y);else x2=x;y2=y; code2 =encode(x,y); displayline（x1,y1,x2,y2）;动画演示：Cohen-Sutherla

4、nd直线段裁剪算法动画演示：Cohen-Sutherland算法和中点分割算法的比较Liang - Barskey算法void LB_LineClip(x1,y1,x2,y2,XL,XR,YB,YT)float x1,y1,x2,y2,XL,XR,YB,YT; float dx,dy,u1,u2; ul=0; u2=1; dx =x2-x1; dy =y2-y1; if(ClipT(-dx,x1-Xl,&u1,&u2) if(ClipT(dx,XR-x1, &u1,&u2) if(ClipT(-dy,y1-YB, &u1,&u2) if(ClipT(dy,YT-y1, &u1,&u2) displayline(x1+u1*dx,y1+u1*dy, x1+u2*dx,y1+u2*dy) return; bool ClipT(p,q,u1,u2)float p,q,*u1,*u2; float r; if(p*u2)return FALSE; else if(r*u1) *u1=r; return TRUE; else if(p0) r=q/p; if(r*u1) return FALSE;