Line Generation (Bresenhams) using OpenGL – Program Source Code

#include<stdlib.h>
#include<GL/glut.h>
#include<math.h>
#include<stdio.h>
void init()
{
 glMatrixMode(GL_PROJECTION);
 gluOrtho2D(0.0,300.0,0.0,300.0);
 glClearColor(0.0,0.0,0.0,0.0);
}
void setpixel(int x,int y)
{
 glBegin(GL_POINTS);
 glVertex2i(x,y);
 glEnd();
 glFlush();
}
void lineBressenham(int xa,int ya,int xb,int yb)
{
 int x,y,xEnd,yEnd;
int dx=abs(xa-xb);
 int dy=abs(ya-yb);
int p=2*dy-dx;
 int twody=2*dy;
 int twodydx=2*(dy-dx);
float m=(float)(yb-ya)/(float)(xb-xa);
if((m>=0) && (m<=1))
 { 
 if(xa>xb)
 {
 x=xb;
 y=yb;
 xEnd=xa;
 }
 else
 {
 x=xa;
 y=ya;
 xEnd=xb;
 }

 setpixel(x,y);
while(x<xEnd)
 {
 x++;
 if(p<0)
 p+=twody;
 else
 {
 y++; 
 p+=twodydx;
 }

 setpixel(x,y);
 }
 }

 else if(m>1)
 {
 if(ya>yb)
 {
 x=xb;
 y=yb;
 yEnd=ya;
 }
 else
 {
 x=xa;
 y=ya;
 yEnd=yb;
 }

 setpixel(x,y);
while(y<yEnd)
 {
 y++;
 if(p<0)
 p+=2*dx;
 else
 {
 x++; 
 p+=2*(dx-dy);
 }

 setpixel(x,y);
 }
 }
else if(m<-1)
 {
 if(ya>yb)
 {
 x=xb;
 y=yb;
 yEnd=ya;
 }
 else
 {
 x=xa;
 y=ya;
 yEnd=yb;
 }

 setpixel(x,y);
while(y<yEnd)
 {
 y--;
 if(p<0)
 p+=2*dx;
 else
 {
 x++; 
 p+=2*(dx-dy);
 }

 setpixel(x,y);
 }
 }
else if((m>=-1) && (m<=0))
 {
 if(xa>xb)
 {
 x=xb;
 y=yb;
 xEnd=xa;
 }
 else
 {
 x=xa;
 y=ya;
 xEnd=xb;
 }

 setpixel(x,y);
while(x<xEnd)
 {
 x++;
 if(p<0)
 p+=twody;
 else
 {
 y--; 
 p+=twodydx;
 }

 setpixel(x,y);
 }
 }

}
void setdata()
{
 int xa,xb,ya,yb; 
 glClear(GL_COLOR_BUFFER_BIT);
 glColor3f(1.0,0.0,0.0);
 glPointSize(4.0);
 printf("Enter the points : ");
 scanf("%d %d %d %d",&xa,&ya,&xb,&yb);
 lineBressenham(xa,ya,xb,yb);
}
int main(int argc,char**argv)
{
 glutInit(&argc,argv);
 glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
 glutInitWindowSize(400,400);
 glutInitWindowPosition(0,0);
 glutCreateWindow("Bressenham Line Algorithm");
 init();
 glutDisplayFunc(setdata);
 glutMainLoop();
 return 0;
}

OUTPUT: