Program to show the implementation of Sutherland-Hodgeman Polygon Clipping Algorithm

 # include <iostream.h>
 # include <graphics.h>
 # include    <conio.h>
 # include     <math.h>


 class PointCoordinates
    {
       public:
      float x;
      float y;

      PointCoordinates( )
         {
        x=0;
        y=0;
         }
    };


 //---------------------------  LineCoordinates  -------------------------//


 class LineCoordinates
    {
       public:
      float x_1;
      float y_1;
      float x_2;
      float y_2;

      LineCoordinates( )
         {
        x_1=0;
        y_1=0;
        x_2=0;
        y_2=0;
         }

      LineCoordinates(const float x1,const float y1,
                          const float x2,const float y2)
         {
        x_1=x1;
        y_1=y1;
        x_2=x2;
        y_2=y2;
         }
    };


 //-------------------------  WindowCoordinates  -------------------------//


 class WindowCoordinates
    {
       public:
      float x_min;
      float y_min;
      float x_max;
      float y_max;

      WindowCoordinates(const float x1,const float y1,
                          const float x2,const float y2)
         {
        x_min=x1;
        y_min=y1;
        x_max=x2;
        y_max=y2;
         }
    };


 void show_screen( );

 void clip_polygon(const WindowCoordinates,const int,const int []);

 const int check_line(const LineCoordinates,const LineCoordinates);
 const int check_point(const LineCoordinates,const float,const float);

 const PointCoordinates get_intersection_point(LineCoordinates,
                                LineCoordinates);

 void Polygon(const int,const int []);
 void Rectangle(const int,const int,const int,const int);
 void Line(const int,const int,const int,const int);


 int main( )
    {
       int driver=VGA;
       int mode=VGAHI;

       initgraph(&driver,&mode,\"..\\\\Bgi\");

       show_screen( );

       WindowCoordinates WC(180,140,470,340);

       setcolor(15);
     Rectangle(WC.x_min,WC.y_min,WC.x_max,WC.y_max);

       int n=10;

       int polygon_vertices[20]={ 100,240 , 180,370 , 210,310 , 380,375 ,
                  520,310 , 480,260 , 510,80  , 280,180 ,
                  210,90  , 100,240 };

       setcolor(7);
     Polygon(n,polygon_vertices);

       setcolor(15);
       settextstyle(0,0,1);
     outtextxy(300,240,\"Window\");
     outtextxy(80,240,\"Polygon\");

       char Key=NULL;

       do
      {
         Key=getch( );
      }
       while(Key!=\'C\' && Key!=\'c\');

       settextstyle(0,0,1);
     setcolor(0);
       outtextxy(163,450,\"  Press \'C\' to see the Clipped Polygon. \");

    setcolor(15);
       outtextxy(163,450,\"------                          ---------\");

     setcolor(12);
       outtextxy(213,450,\"  Press any Key to exit.  \");

       clip_polygon(WC,n,polygon_vertices);

       setcolor(15);
       settextstyle(0,0,1);
     outtextxy(280,155,\"Clipped Polygon\");

       getch( );
       return 0;
    }



 //--------------------------  clip_polygon( )  --------------------------//


 void clip_polygon(const WindowCoordinates wc,const int n,
                         const int polygon_edges[])
    {
       int edges_counter;
       int number_of_edges=n;

       int *edges=new int[(n*4)];
       int *clipped_edges=new int[(n*4)];

       for(int count_1=0;count_1<(n*2);count_1++)
      edges[count_1]=polygon_edges[count_1];

       LineCoordinates window_line;

       for(int count_2=1;count_2<=4;count_2++)
      {
         edges_counter=1;

         for(int count_3=0;count_3<(number_of_edges*4);count_3++)
        clipped_edges[count_3]=0;

         if(count_2==1)
        {
           window_line.x_1=wc.x_min;
           window_line.y_1=wc.y_max;
           window_line.x_2=wc.x_max;
           window_line.y_2=wc.y_max;
        }

         else if(count_2==2)
        {
           window_line.x_1=wc.x_max;
           window_line.y_1=wc.y_max;
           window_line.x_2=wc.x_max;
           window_line.y_2=wc.y_min;
        }

         else if(count_2==3)
        {
           window_line.x_1=wc.x_max;
           window_line.y_1=wc.y_min;
           window_line.x_2=wc.x_min;
           window_line.y_2=wc.y_min;
        }

         else if(count_2==4)
        {
           window_line.x_1=wc.x_min;
           window_line.y_1=wc.y_min;
           window_line.x_2=wc.x_min;
           window_line.y_2=wc.y_max;
        }

         int rule_no;

         PointCoordinates point;

         for(int count_4=1;count_4<number_of_edges;count_4++)
        {
           LineCoordinates line(edges[((count_4*2)-2)],
                    edges[((count_4*2)-1)],
                    edges[(count_4*2)],
                    edges[((count_4*2)+1)]);

           rule_no=check_line(window_line,line);

           switch(rule_no)
              {
             case 1 : clipped_edges[(edges_counter*2)]=
                             (int)(line.x_2+0.5);
                  clipped_edges[((edges_counter*2)+1)]=
                             (int)(line.y_2+0.5);
                  edges_counter++;
                  break;

             case 2 : break;

             case 3 : point=
                    get_intersection_point(window_line,line);

                  clipped_edges[(edges_counter*2)]=
                              (int)(point.x+0.5);
                  clipped_edges[((edges_counter*2)+1)]=
                              (int)(point.y+0.5);
                  edges_counter++;
                  break;

             case 4 : point=
                    get_intersection_point(window_line,line);

                  clipped_edges[(edges_counter*2)]=
                              (int)(point.x+0.5);
                  clipped_edges[((edges_counter*2)+1)]=
                              (int)(point.y+0.5);
                  edges_counter++;

                  clipped_edges[(edges_counter*2)]=
                             (int)(line.x_2+0.5);
                  clipped_edges[((edges_counter*2)+1)]=
                             (int)(line.y_2+0.5);
                  edges_counter++;
                  break;
              }
        }

         clipped_edges[0]=clipped_edges[((edges_counter*2)-2)];
         clipped_edges[1]=clipped_edges[((edges_counter*2)-1)];

         for(int count_5=0;count_5<(edges_counter*2);count_5++)
        edges[count_5]=0;

         number_of_edges=edges_counter;

         for(int count_6=0;count_6<(edges_counter*2);count_6++)
        edges[count_6]=clipped_edges[count_6];
     }

       setcolor(10);
     Polygon(number_of_edges,edges);

       delete edges;
       delete clipped_edges;
    }


 //----------------------------  check_line( )  --------------------------//


 const int check_line(const LineCoordinates line,const LineCoordinates edge)
    {
       int rule_number=0;
       int point_1=check_point(line,edge.x_1,edge.y_1);
       int point_2=check_point(line,edge.x_2,edge.y_2);

       if(point_1==1 && point_2==1)
      rule_number=1;

       else if(point_1!=1 && point_2!=1)
      rule_number=2;

       else if(point_1==1 && point_2!=1)
      rule_number=3;

       else if(point_1!=1 && point_2==1)
      rule_number=4;

       return rule_number;
    }


 //----------------------------  check_point( )  -------------------------//


 const int check_point(const LineCoordinates lc,const float x,const float y)
    {
       float c=(((lc.x_2-lc.x_1)*(y-lc.y_1))-((lc.y_2-lc.y_1)*(x-lc.x_1)));

       if(c<=0)
      return 1;

       else
      return 0;
    }


 //----------------------  get_intersection_point( )  --------------------//


 const PointCoordinates get_intersection_point(LineCoordinates lc1,
                            LineCoordinates lc2)
    {
       float x_min=lc1.x_1;
       float x_max=lc1.x_2;
       float y_min=lc1.y_1;
       float y_max=lc1.y_2;

       if(lc1.x_1==lc1.x_2)
      {
         if(lc2.y_2>=lc2.y_1 && lc2.y_2>y_max)
        y_max=lc2.y_2;

         else if(lc2.y_1>lc2.y_2 && lc2.y_1>y_max)
        y_max=lc2.y_1;

         if(lc2.y_1<=lc2.y_2 && lc2.y_1<y_min)
        y_min=lc2.y_1;

         else if(lc2.y_2<lc2.y_1 && lc2.y_2<y_min)
        y_min=lc2.y_2;
      }

       else if(lc1.y_1==lc1.y_2)
      {
         if(lc2.x_2>=lc2.x_1 && lc2.x_2>x_max)
        x_max=lc2.x_2;

         else if(lc2.x_2<lc2.x_1 && lc2.x_1>x_max)
        x_max=lc2.x_1;

         if(lc2.x_1<=lc2.x_2 && lc2.x_1<x_min)
        x_min=lc2.x_1;

         else if(lc2.x_2<lc2.x_1 && lc2.x_2<x_min)
        x_min=lc2.x_2;
      }

       float x_mid;
       float y_mid;

       if(lc2.y_1>y_max)
      {
         while(lc2.y_1!=y_max)
        {
           x_mid=((lc2.x_1+lc2.x_2)/2);
           y_mid=((lc2.y_1+lc2.y_2)/2);

           if(y_mid>=y_max)
              {
             lc2.x_1=x_mid;
             lc2.y_1=y_mid;
              }

           else
              {
             lc2.x_2=x_mid;
             lc2.y_2=y_mid;
              }
        }
      }

       else if(lc2.y_1<y_min)
      {
         while(lc2.y_1!=y_min)
        {
           x_mid=((lc2.x_1+lc2.x_2)/2);
           y_mid=((lc2.y_1+lc2.y_2)/2);

           if(y_mid<=y_min)
              {
             lc2.x_1=x_mid;
             lc2.y_1=y_mid;
              }

           else
              {
             lc2.x_2=x_mid;
             lc2.y_2=y_mid;
              }
        }
      }

       if(lc2.x_1>x_max)
      {
         while(lc2.x_1!=x_max)
        {
           x_mid=((lc2.x_1+lc2.x_2)/2);
           y_mid=((lc2.y_1+lc2.y_2)/2);

           if(x_mid>=x_max)
              {
             lc2.x_1=x_mid;
             lc2.y_1=y_mid;
              }

           else
              {
             lc2.x_2=x_mid;
             lc2.y_2=y_mid;
              }
        }
      }

       else if(lc2.x_1<x_min)
      {
         while(lc2.x_1!=x_min)
        {
           x_mid=((lc2.x_1+lc2.x_2)/2);
           y_mid=((lc2.y_1+lc2.y_2)/2);

           if(x_mid<=x_min)
              {
             lc2.x_1=x_mid;
             lc2.y_1=y_mid;
              }

           else
              {
             lc2.x_2=x_mid;
             lc2.y_2=y_mid;
              }
        }
      }

       PointCoordinates ipt;

       ipt.x=lc2.x_1;
       ipt.y=lc2.y_1;

       return ipt;
    }



 //---------------------------  Rectangle( )  ----------------------------//


 void Rectangle(const int x_1,const int y_1,const int x_2,const int y_2)
    {
       Line(x_1,y_1,x_2,y_1);
       Line(x_2,y_1,x_2,y_2);
       Line(x_2,y_2,x_1,y_2);
       Line(x_1,y_2,x_1,y_1);
    }


 //-----------------------------  Polygon( )  ----------------------------//


 void Polygon(const int n,const int coordinates[])
    {
       if(n>=2)
      {
         Line(coordinates[0],coordinates[1],
                         coordinates[2],coordinates[3]);

         for(int count=1;count<(n-1);count++)
        Line(coordinates[(count*2)],coordinates[((count*2)+1)],
                        coordinates[((count+1)*2)],
                        coordinates[(((count+1)*2)+1)]);
      }
    }


 //--------------------------  Line( )  ------------------------//


 void Line(const int x_1,const int y_1,const int x_2,const int y_2)
    {
       int color=getcolor( );

       int x1=x_1;
       int y1=y_1;

       int x2=x_2;
       int y2=y_2;

       if(x_1>x_2)
      {
         x1=x_2;
         y1=y_2;

         x2=x_1;
         y2=y_1;
      }

       int dx=abs(x2-x1);
       int dy=abs(y2-y1);
       int inc_dec=((y2>=y1)?1:-1);

       if(dx>dy)
      {
         int two_dy=(2*dy);
         int two_dy_dx=(2*(dy-dx));
         int p=((2*dy)-dx);

         int x=x1;
         int y=y1;

         putpixel(x,y,color);

         while(x<x2)
        {
           x++;

           if(p<0)
              p+=two_dy;

           else
              {
             y+=inc_dec;
             p+=two_dy_dx;
              }

           putpixel(x,y,color);
        }
      }

       else
      {
         int two_dx=(2*dx);
         int two_dx_dy=(2*(dx-dy));
         int p=((2*dx)-dy);

         int x=x1;
         int y=y1;

         putpixel(x,y,color);

         while(y!=y2)
        {
           y+=inc_dec;

           if(p<0)
              p+=two_dx;

           else
              {
             x++;
             p+=two_dx_dy;
              }

           putpixel(x,y,color);
        }
      }
    }


 //--------------------------  show_screen( )  ---------------------------//


 void show_screen( )
    {
       setfillstyle(1,1);
     bar(125,26,510,38);

       settextstyle(0,0,1);
     setcolor(15);
       outtextxy(5,5,\"******************************************************************************\");
       outtextxy(5,17,\"*-**************************************************************************-*\");
       outtextxy(5,29,\"*-------------                                                  -------------*\");
       outtextxy(5,41,\"*-**************************************************************************-*\");
       outtextxy(5,53,\"*-**************************************************************************-*\");

     setcolor(11);
       outtextxy(134,29,\"Sutherland-Hodgeman Polygon Clipping Algorithm\");

     setcolor(15);

       for(int count=0;count<=30;count++)
          outtextxy(5,(65+(count*12)),\"*-*                                                                        *-*\");

       outtextxy(5,438,\"*-**************************************************************************-*\");
       outtextxy(5,450,\"*-------------------                                         ----------------*\");
       outtextxy(5,462,\"******************************************************************************\");

     setcolor(12);
       outtextxy(163,450,\"  Press \'C\' to see the Clipped Polygon. \");
    }