4.7.2.c

计算机图形学

/*4.7.2、中点分割算法    */
#include <math.h>
#include"stdio.h"
#include "Conio.h"
#include "graphics.h"
void initgr(void) /* BGI初始化 */
{ int gd=DETECT, gm=0;
  registerbgidriver(EGAVGA_driver);
  initgraph(&gd, &gm, "");
}
int encode(int x,int y,int xl,int xr,int yb,int yt)
{int c=0;
 if (x<xl) c=c|1;
 else if (x>xr) c=c|2;
 if (y<yb) c=c|4;
 else if (y>yt) c=c|8;
 return c;
}
struct point
{int x;
 int y;};
struct point *edgepoint(int x1,int y1,int x2,int y2,int xl,int xr,int yb,int yt)
{struct point *pt;
 int code1,code2,code;
 int xx,yy;
 long d,d1,d2;
 pt=(struct point *)malloc(sizeof(struct point));
 code1=encode(x1,y1,xl,xr,yb,yt);
 code2=encode(x2,y2,xl,xr,yb,yt);
 if (code1==0)/*(x1,y1)在裁剪窗口内,返回该点*/
  {xx=x1; yy=y1;
   pt->x=xx; pt->y=yy;
   return pt;
  }
 if ((code1&code2)!=0) return NULL;
 do{
    xx=(x1+x2)/2;
    yy=(y1+y2)/2;
    code=encode(xx,yy,xl,xr,yb,yt);
    d1=(yy-y1)*(yy-y1);
    d2=(xx-x1)*(xx-x1);
    d=sqrt(d1+d2);
    pt->x=xx;pt->y=yy;
    if((code&code1)!=0)
      {x1=xx;y1=yy;
       }
    else{x2=xx;
         y2=yy;}
   }while(d>1);
 return pt;
}


main()
{ int xl,xr,yt,yb;
  int x1,y1,x2,y2;
  struct point *p1,*p2;
  initgr();
  printf("Enter the left,right,buttom,top edge:");
  scanf("%d,%d,%d,%d",&xl,&xr,&yb,&yt);
  setcolor(12);
  line(xl,yt,xr,yt);  line(xl,yb,xr,yb);
  line(xl,yt,xl,yb);  line(xr,yt,xr,yb);
  printf("Enter the first point of the line:");
  scanf("%d,%d",&x1,&y1);
  printf("Enter the second point of the line:");
  scanf("%d,%d",&x2,&y2);
  setcolor(1);
  line(x1,y1,x2,y2);
  /*求出最靠近(x1,y1)的内点*/
  p1=edgepoint(x1,y1,x2,y2,xl,xr,yb,yt);
  /*求出最靠近(x2,y2)的内点*/
  p2=edgepoint(x2,y2,p1->x,p1->y,xl,xr,yb,yt);
  setcolor(14);
  if(p1!=NULL&&p2!=NULL)
     line(p1->x,p1->y,p2->x,p2->y);
  else
     printf("\nthe line is invisiable.");
  getch();
  closegraph();
}