#include <iostream>
#include <stdlib.h>
#include <GL/glut.h>

using namespace std;

void drawfunc(void);
void keyfunc(unsigned char, int, int);
void myglinit(void);

char *easel;
int width, height;

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

  // width and height of the window
  width = height = 256;

  // create a char buffer, 3 bytes per pixel of the window
  easel = new char[width*height*3];
  
  // initialize the glut system and create a window
  glutInitWindowSize(width, height);
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
  glutCreateWindow("example");

  // initialize some OpenGL state
  myglinit();
  
  // set callback functions.  drawfunc is the function that gets
  // called automatically as fast as possible.  keyfunc only is
  // invoked if the user hits a keyboard key.

  glutDisplayFunc(drawfunc);
  glutKeyboardFunc(keyfunc);
  
  // start the main glut loop, no code runs after this
  glutMainLoop();
  
}

void setpixel(char *buf, int x, int y, int r, int g, int b) {

  buf[(y*width+x)*3+0] = r;
  buf[(y*width+x)*3+1] = g;
  buf[(y*width+x)*3+2] = b;

}

// main draw function, gets called over and over, as fast as possible
void drawfunc(void) {
  int i,j;

  cout << "in drawfunc" << endl;

  // set first half of buffer to red
  for (i=0; i<width/2; i++) {
    for (j=0; j<height; j++) {
      // set pixel at coord i,j to 'red'
      setpixel(easel, i, j, 255, 0, 0);
    }
  }

  // set second half to green
  for (i=width/2; i<width; i++) {
    for (j=0; j<height; j++) {
      // set pixel at coord i,j to 'green'
      setpixel(easel, i, j, 0, 255, 0);
    }
  }

  // drawpixels draws the rgb data stored in 'easel' to the screen
  glDrawPixels(width, height, GL_RGB, GL_UNSIGNED_BYTE, easel);


  // in double buffer mode so we swap to avoid a flicker
  glutSwapBuffers();

  // instruct event system to call 'drawfunc' again
  glutPostRedisplay();
}

void keyfunc(unsigned char k, int x, int y) {

  cout << "in keyfunc" << endl;

  switch (k) {
  case 27:
    // escape key
    exit(0);
    break;
  case GLUT_KEY_UP:
    // up arrow
    break;
  case 'a':
    // 'a' key
    break;
  }

}

// set some OpenGL state variables
void myglinit() {


  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();

  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();

  glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
  glClear(GL_COLOR_BUFFER_BIT);

}