多边形裁剪

[c]代码库

 #include"conio.h"
#include"graphics.h"
#define right 1
#define bottom 2
#define left 3
#define top 4
#define N 20
void clip_polygon (int Xwmax,int Xwmin,int Ywmax,int Ywmin,int& n,int *x,int *y);
void clip_single_edge(int edge,int type,int& nin,int *xin,int *yin,int& nout,int *xout,int *yout);
void test_intersect(int edge,int type,int x1,int y1,int x2, int y2, int& xout,int& yout,int& yes,int& is_in);
void main()
{  
   int i;
   int xwmax=400, xwmin=200,ywmax=400,ywmin=200,n=7;
   int x[]={500,300,300,100,351,80,380};
   int y[]={320,125,450,320,242,420,350};
   initgraph(640,640);
   setcolor(YELLOW);
   rectangle(200,200,400,400);
   outtextxy(200,20,"按回车键开始剪裁");
   setcolor(RED);
   for(i=0;i<n;i++)
   {
     moveto(x[i],y[i]);
  if(i+1!=n)
       lineto(x[i+1],y[i+1]);
  else lineto(x[0],y[0]);
   }
   getch(); 
  cleardevice();
   setcolor(YELLOW);
   rectangle(200,200,400,400);
   clip_polygon(xwmax,xwmin,ywmax,ywmin,n,x,y);
   getch();
   closegraph();
}
void clip_polygon (int Xwmax,int Xwmin,int Ywmax,int Ywmin,int& n,int *x,int *y)
{  int x1[N],y1[N],x2[N],y2[N],n1;
   clip_single_edge(Xwmax,right,n,x,y,n1,x1,y1);
   clip_single_edge(Ywmax,bottom,n1,x1,y1,n1,x2,y2);
   clip_single_edge(Xwmin,left,n1,x2,y2,n1,x1,y1);
   clip_single_edge(Ywmin,top,n1,x1,y1,n1,x2,y2);
   setcolor(GREEN);
   for(int i=0;i<n1;i++)
   {
     moveto(x2[i],y2[i]);
   if(i+1!=n1)
   lineto(x2[i+1],y2[i+1]);
   else lineto(x2[0],y2[0]);
   }
}           
void clip_single_edge(int edge,int type,int& nin,int *xin,int *yin,int& nout,int *xout,int *yout)
{
  int  k=0, yes, is_in;
  int x, y, x_intersect, y_intersect;
   x=xin[nin-1];y=yin[nin-1];
       
  for(int j=0; j<nin; j++)
    {
       test_intersect(edge, type, x, y,xin[j], yin[j],x_intersect,y_intersect,yes,is_in);
       if(yes) 
          {
             xout[k]=x_intersect;
             yout[k]=y_intersect;
             k++; 
          }
         if(is_in) 
            {  
               xout[k]=xin[j];
               yout[k]=yin[j];
               k++;
            }
        x=xin[j];    
        y=yin[j];
     }
  nout=k;
}
void test_intersect(int edge,int type,int x1,int y1,int x2, int y2, int& xout,int&  yout,int&  yes,int&  is_in)
{
   float m; 
   is_in=yes=0;
   if(x1!=x2)
   m=(float)((float)y2-(float)y1)/((float)x2-(float)x1);
   switch(type)
     { 
        case right :
             if (x2<edge)
                {   
                  is_in=1;
                  if(x1>edge) 
                      yes=1;
                }
               else
                if(x1<=edge)
                  yes=1;
                  break; 
        case bottom: 
             if(y2<=edge) 
               { 
                  is_in=1; 
                  if(y1>edge)
                  yes=1;  
               } 
              else 
                if(y1<=edge)
                   yes=1;
                   break;
        case left: 
             if(x2>=edge) 
               { 
                  is_in=1; 
                  if(x1<edge)  
                  yes=1; 
               }
              else
                if(x1>=edge)
                  yes=1;
                  break; 
        case top :
             if(y2>=edge)
               {
                  is_in=1;
                  if(y1<edge)
                  yes=1; 
               }
              else
                if(y1>=edge)
                   yes=1;
       default: break;
    }
    if(yes)
       if((type==right) || (type==left)) 
          {
             xout = edge;
             yout=(y1+m*(xout-x1));
          }
    else 
      if(x1==x2)
   {      
           if(type==2&&(y1<=edge||y2<=edge))
     {xout=x1;yout=edge;}
     if(type==4&&(y1>=edge||y2>=edge))
     {xout=x1;yout=edge;}
   }
         else
           {  
              yout=edge; xout=x1+(yout-y1)/m; 
           }
  }