/* W B Langdon at MUN 10 May 2007
 * Program to demonstarte use of OpenGL's glDrawPixels
 */

/* modified for animation by Sam Watkins.
   refs:
     http://www.cs.mun.ca/~blangdon/opengl/glDrawPixels.html
     http://www.gamedev.net/community/forums/topic.asp?topic_id=470849
     http://www.rage3d.com/board/showthread.php?t=33651848
*/

  //http://msdn2.microsoft.com/en-us/library/ms537062.aspx
  //glDrawPixels writes a block of pixels to the framebuffer.

#include <GL/gl.h>
#include <GL/glext.h>
#include <GL/glut.h>

//#include <iostream>
//#include <sstream>
#include "stdio.h"
#include "stdlib.h"
#include "math.h"
#include "string.h"
#include <unistd.h>
#include <sys/time.h>

unsigned int window_width = 1024, window_height = 768;
int size;
unsigned long *pixels;

double last_time = 0;

//WBL 9 May 2007 Based on
//http://www.codeguru.com/cpp/w-d/dislog/commondialogs/article.php/c1861/
//Common.h

//Convert a wide range of data values into nice colours 
void colour(const float data, unsigned char * out) {
  //convert data to angle
  out[0] = 128 + data*128/10;
  out[1] = 64 - data*64/10;
  out[2] = 32;
  out[3] = 128;
}

int frame = 0;

//#define rgb(r,g,b) ((r)<<24|(g)<<16|(b)<<8)
#define rgb(r,g,b) ((b)<<16|(g)<<8|(r))

void animate()
{
  unsigned long *px = pixels;
  unsigned char  r = frame, g = frame, b = -frame;
  int x, y;
  for(y=0; y<window_height; ++y) {
    for(x=0; x<window_width; ++x) {
//      *px = 7654321;
//      *px = rgb((x+frame)&255,(y+frame)&255,(x+y-frame)&255);
      *px++ = rgb(r++,g,b++);
    }
    g++; b++;
  }
  r++; g++; b--;
  if (frame % 100 == 0) {
    double t;
    struct timeval tv;
    gettimeofday(&tv, NULL);
    t = tv.tv_sec + tv.tv_usec * 1e-6;
    if (last_time != 0) {
      double fps = 100.0/(t - last_time);
      fprintf(stderr, "fps: %f\n", fps);
    }
    last_time = t;
  }
  ++frame;
}

void invert_pixels(unsigned long *to, unsigned long *from)
{
  // hack around GL's inability to plot pixmaps "upside-down" (up the right way) at reasonable speed
  // this is crap, but it's a lot faster than glPixelZoom
  // I will hack brace so that I always use stride, and can use negative stride for GL buffers.
  int y;
  to += window_width*(window_height-1);
  for(y=0; y<window_height; ++y) {
    memcpy(to, from, window_width*4);
    to -= window_width;
    from += window_width;
  }
}

void display()
{
//  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  unsigned long upsidedown[size];
  invert_pixels(upsidedown, pixels);  // !@#$@$#!@#$
  glDrawPixels(window_width,window_height,GL_RGBA,GL_UNSIGNED_BYTE,upsidedown);

  glutSwapBuffers();
  glFlush();
}

void idle()
{
  animate();
  glutPostRedisplay();
//  fprintf(stderr, "frame %d  ", frame);
}

int main(int argc, char** argv) {
  size = window_width * window_height;
  pixels = malloc(4 * size);
  pixels += window_width;
  if (!pixels) {
    fprintf(stderr, "malloc failed\n");
    exit(1);
  }

  glutInit(&argc, argv);

  glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
  glutInitWindowSize(window_width, window_height);
  glutCreateWindow("OpenGL glDrawPixels demo");

  glDisable(GL_DEPTH_TEST);
  glDepthMask(GL_FALSE);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(0,1,1,0,-1,1);
//  glMultMatrixf((GLfloat[]){1,0,0,0,0,-1,0,0,0,0,1,0,0,0,0,1});
//  glPixelZoom(1.0, -1.0);
//  glRasterPos2f(0, 1); // window_height);

  glutDisplayFunc(display);
  //glutReshapeFunc(reshape);
  //glutMouseFunc(mouse_button);
  //glutMotionFunc(mouse_motion);
  //glutKeyboardFunc(keyboard);
  glutIdleFunc(idle);
  
  glClearColor(0.0, 0.0, 0.0, 1.0);
  //glPointSize(2);

  glutMainLoop();
}