Liang-Barsky Line Clipping Graphics Algorithm

Computer graphics program in C++

Liang-Barsky Line Clipping Algorithm using C++ graphics library

C++

# include <iostream>
 # include<graphics.h>
 # include<conio.h>
 # include<math.h>
using namespace std;

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

      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;
         }
};
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;
         }
};

const int clip_line(const WindowCoordinates,LineCoordinates&);
const int check_line(const float,const float,float&,float&);
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,"");
       WindowCoordinates WC(200,150,450,350);
       setcolor(15);
       Rectangle(WC.x_min,WC.y_min,WC.x_max,WC.y_max);
       LineCoordinates LC_1(150,160,120,320);
       LineCoordinates LC_2(250,100,150,200);
       LineCoordinates LC_3(160,200,490,260);
       LineCoordinates LC_4(300,300,400,380);
       LineCoordinates LC_5(550,300,450,400);
       LineCoordinates LC_6(440,110,400,370);
       setcolor(6);
       Line(LC_1.x_1,LC_1.y_1,LC_1.x_2,LC_1.y_2);
       Line(LC_2.x_1,LC_2.y_1,LC_2.x_2,LC_2.y_2);
       Line(LC_3.x_1,LC_3.y_1,LC_3.x_2,LC_3.y_2);
       Line(LC_4.x_1,LC_4.y_1,LC_4.x_2,LC_4.y_2);
       Line(LC_5.x_1,LC_5.y_1,LC_5.x_2,LC_5.y_2);
       Line(LC_6.x_1,LC_6.y_1,LC_6.x_2,LC_6.y_2);
       char Key=NULL;
       do
       {
         Key=getch( );
       }
       while(Key!='1');
       setcolor(14);
       if(clip_line(WC,LC_1))
       Line(LC_1.x_1,LC_1.y_1,LC_1.x_2,LC_1.y_2);

       if(clip_line(WC,LC_2))
       Line(LC_2.x_1,LC_2.y_1,LC_2.x_2,LC_2.y_2);

       if(clip_line(WC,LC_3))
       Line(LC_3.x_1,LC_3.y_1,LC_3.x_2,LC_3.y_2);

       if(clip_line(WC,LC_4))
       Line(LC_4.x_1,LC_4.y_1,LC_4.x_2,LC_4.y_2);

       if(clip_line(WC,LC_5))
       Line(LC_5.x_1,LC_5.y_1,LC_5.x_2,LC_5.y_2);

       if(clip_line(WC,LC_6))
       Line(LC_6.x_1,LC_6.y_1,LC_6.x_2,LC_6.y_2);

       getch( );
       return 0;
}

const int clip_line(const WindowCoordinates wc,LineCoordinates &lc)
{
       float u_1=0;
       float u_2=1;

       float dx=(lc.x_2-lc.x_1);
       float dy=(lc.y_2-lc.y_1);

       float p1=(-dx);
       float p2=dx;
       float p3=(-dy);
       float p4=dy;

       float q1=(lc.x_1-wc.x_min);
       float q2=(wc.x_max-lc.x_1);
       float q3=(lc.y_1-wc.y_min);
       float q4=(wc.y_max-lc.y_1);

       if(check_line(p1,q1,u_1,u_2) && check_line(p2,q2,u_1,u_2) &&
             check_line(p3,q3,u_1,u_2) && check_line(p4,q4,u_1,u_2))
      {
         if(u_2<1)
        {
           lc.x_2=(lc.x_1+(u_2*dx));
           lc.y_2=(lc.y_1+(u_2*dy));
        }

         if(u_1>0)
        {
           lc.x_1+=(u_1*dx);
           lc.y_1+=(u_1*dy);
        }

         lc.x_1=(int)(lc.x_1+0.5);
         lc.y_1=(int)(lc.y_1+0.5);
         lc.x_2=(int)(lc.x_2+0.5);
         lc.y_2=(int)(lc.y_2+0.5);

         return 1;
      }

       return 0;
}

const int check_line(const float p,const float q,float &u_1,float &u_2)
{
       int flag=1;

       float r=(q/p);

       if(p<0)
      {
         if(r>u_2)
        flag=0;

         else if(r>u_1)
        u_1=r;
      }

       else if(p>0)
      {
         if(r<u_1)
        flag=0;

         else if(r<u_2)
        u_2=r;
      }

       else
      {
         if(q<0)
        flag=0;
      }

       return flag;
}

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);
}

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);
        }
      }
}