2. bresenham line.cpp

#include<iostream>
#include<math.h>
#include<GL/gl.h>
#include<GL/glut.h>

 using namespace std;
 
 
  struct point
  {
    int x;
    int y;
    
   } ;
   point p1,p2;
   
   void bresenham(point p1 , point p2)
   {
      int dx , dy , x , y , xinc , yinc;
      int e , inc1 , inc2;
      
      dx = p2.x - p1.x;
      dy = p2.y - p1.y;
      
      xinc = (p2.x >p1.x ) ? 1 : -1;
      yinc = (p2.y >p1.y ) ? 1 : -1;
      
      x=p1.x;
      y=p1.y;
      
      glBegin(GL_POINTS);
      glVertex2i(x , y);
      
      if(dx >=dy)
      {
        e = 2*dy - dx;
        inc1 = 2 *(dy-dx);
        inc2 = 2 * dy;
        
        for(int i=0 ; i<dx ; i++)
        {
           if(e>=0)
           {
              y += yinc;
              e +=inc1;
           }else
           {
              e +=inc2;
           }
           x += xinc;
           
           
           if(i%9!=0 &&i%10!=0 && i%11!=0 &&i%12!=0 &&i%16!=0&&i%17!=0 && i%18!=0&&i%19!=0)
		{
			glVertex2i(x,y);
		}
        }
      
      
       
   }else
   {
       
        e = 2*dx - dy;
        inc1 = 2 *(dx- dy);
        inc2 = 2 * dx;
        
        for(int i=0 ; i<dy ; i++)
        {
           if(e>=0)
           {
               x += xinc;
              e +=inc1;
           }else
           {
              e +=inc2;
           }
          
           y += yinc;
           
           
           if(i%9!=0 &&i%10!=0 && i%11!=0 &&i%12!=0 &&i%16!=0&&i%17!=0 && i%18!=0&&i%19!=0)
		{
			glVertex2i(x,y);
		}
        
      }
       
     }
     glEnd();
      glFlush();
   }
   
   void init()
   {
      glClearColor(0.0 , 0.0 , 0.0 , 1.0);
      glColor3f(1.0 , 0.0 ,0.0);
      glPointSize(2.0);
      glMatrixMode(GL_PROJECTION);
      gluOrtho2D(0.0 , 640.0 , 0.0 , 480.0);
      glClear(GL_COLOR_BUFFER_BIT);
      glFlush();
      
   }
   
     int main(int argc , char **argv)
     {
        glutInit(&argc , argv);
        glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
        glutInitWindowSize(640 , 480);
        glutInitWindowPosition(0,0);
        glutCreateWindow("Bresenham");
        
        init();
        
       glBegin(GL_LINES);
		glVertex2i(0,240);
		glVertex2i(640,240);
		glVertex2i(320,0);
		glVertex2i(320,480);
        
        glEnd();
        glFlush();
        
        cout<<"\nEnter the Initial Co-ordinates\n Enter the X cordinate and Y coordinate";
        cin>>p1.x>>p1.y;
        
         cout<<"\nEnter the Final Co-ordinates\n Enter the X cordinate and Y coordinate";
        cin>>p2.x>>p2.y;
        
        
        p1.x+=320;
	p2.y+=240;
	p2.x+=320;
	p1.y+=240;
	glColor3f(0.0,1.0,1.0);
        bresenham(p1 , p2);
        glutMainLoop();
        
        
     }