#define BLACK 0
#include <GL/glut.h>
#include <stdio.h>

void draw_pixel(int ix, int iy, int value)
{
  glBegin(GL_POINTS);
    glVertex2i( ix, iy);
  glEnd();
}

void lineDDA(int x1, int y1, int xn, int yn)
{
     int dx, dy, m, i;
     m = (yn-y1)/(xn-x1);
     for (i=x1; i<=xn; i++)
     {
          if (m <= 1)
          {
               dx = 1;
               dy = m * dx;
             }
             else
             {
                  dy = 1;
                  dx = dy / m;
             }
             x1 = x1 + dx;
             y1 = y1 + dy;
             draw_pixel(x1, y1, BLACK);
             }
}

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);
    lineDDA(0, 100, 100, 200);
    glFlush();
}

void myinit()
{
    glClearColor(1.0, 1.0, 1.0, 1.0);
    glColor3f(1.0, 0.0, 0.0);
    glPointSize(1.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0.0, 499.0, 0.0, 499.0);
}

int main(int argc, char** argv)
{

/* standard GLUT initialization */

    glutInit(&argc;,argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); /* default, not needed */
    glutInitWindowSize(500,500); /* 500x500 pixel window */
    glutInitWindowPosition(0,0); /* place window top left on display */
    glutCreateWindow("Bresenham's Algorithm"); /* window title */
    glutDisplayFunc(display); /* display callback invoked when window opened */

    myinit(); /* set attributes */

    glutMainLoop(); /* enter event loop */
}