#include<GL/gl.h>
#include<GL/glu.h>
#include<GL/glut.h>
#include<stdlib.h>

void drawDot(GLint x, GLint y);

const int screenWidth = 640;
const int screenHeight = 480;

void drawDot(GLint x, GLint y)
{
  glBegin(GL_POINTS);
    glVertex2i(x,y);
  glEnd();
  glFlush();
}

void myMouse(int button, int state, int x, int y)
{
  if(button == GLUT_LEFT_BUTTON && state == GLUT_DOWN)
    drawDot(x, screenHeight - y);
  else if(button == GLUT_RIGHT_BUTTON && state == GLUT_DOWN)
    exit(-1);
}

void myDisplay(void)
{
  glClear(GL_COLOR_BUFFER_BIT);  // clear the screen
}

void myInit(void)
{
  glClearColor(1.0,1.0,1.0,0.0); // background
  glColor3f(0.0, 0.0, 0.0);   // drawing color
  glPointSize(4.0);              // pointsize
  glMatrixMode(GL_PROJECTION);   // random necessary wierdness
  glLoadIdentity();                    
  gluOrtho2D(0.0, 640.0, 0.0, 480.0);  
}

void main(int argc, char** argv)
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
  glutInitWindowSize(640, 480);
  glutInitWindowPosition(100, 150);
  glutCreateWindow("place dots with mouse:");
  glutMouseFunc(myMouse);
  glutDisplayFunc(myDisplay);
  myInit();
  glutMainLoop();
}