// opengl_example.cpp : Defines the entry point for the console application.

//

#include "stdafx.h"

//#include <stdlib.h>

//#include <windows.h>

#include "cv.h"

#include "highgui.h"

#include <GL/glut.h>

void init(void) 

{

   glClearColor (0.0, 0.0, 0.0, 0.0);

   glShadeModel (GL_FLAT);

   glEnable(GL_CULL_FACE);

}

void display(void)

{

   glClear (GL_COLOR_BUFFER_BIT);

   glColor3f (1.0, 1.0, 1.0);

   glLoadIdentity ();             /* clear the matrix */

           /* viewing transformation  */

   glTranslated(0, 0, -25);

   //glScalef (1.0, 2.0, 1.0);      /* modeling transformation */ 

   glBegin(GL_QUADS);                // Draw A Quad

    glVertex3f(-10.0f, 10.0f, 0.0f);                                // Top Left

    glVertex3f(-10.0f,-10.0f, 0.0f);                                // Bottom Left

    glVertex3f( 10.0f,-10.0f, 0.0f);                                // Bottom Right

    glVertex3f( 10.0f, 10.0f, 0.0f);                                // Top Right

  glEnd();

   glFlush ();

}

void reshape (int w, int h)

{

   glViewport (0, 0, (GLsizei) w, (GLsizei) h); 

   glMatrixMode (GL_PROJECTION);

   glLoadIdentity ();

   gluPerspective(90, (double)w/h, 5.0, 400.0);

   glMatrixMode (GL_MODELVIEW);

   gluLookAt(0.0, 0.0, 0.0, 0.0, 0.0, -400.0, 0.0, 1.0, 0.0);

}

void keyboard(unsigned char key, int x, int y)

{

   switch (key) {

      case 27:

         exit(0);

         break;

   }

}

int main(int argc, char** argv)

{

  int screenWidth = 512, screenHeight = 512;

  glutInit(&argc, argv);

  glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);

  glutInitWindowSize (screenWidth, screenHeight); 

  glutInitWindowPosition (100, 100);

  glutCreateWindow (argv[0]);

  init ();

  //glutDisplayFunc(display); 

  //glutReshapeFunc(reshape);

  //glutKeyboardFunc(keyboard);

  //glutMainLoop();

  reshape (screenWidth, screenHeight);

  int error_code = glGetError();  // Error Code: 0, NO Error

  glDrawBuffer(GL_FRONT);

  display();

  //glPushClientAttrib(GL_CLIENT_ALL_ATTRIB_BITS);

  cv::Mat image1;

  image1.create(screenHeight,screenWidth, CV_8UC3);

  glReadPixels(0, 0, screenWidth, screenHeight, GL_BGR_EXT, GL_UNSIGNED_BYTE, (uchar*)image1.data);

  int error_code1 = glGetError();  // Error Code: 0, NO Error

  //glPopClientAttrib();

  const char *title = "glReadPixels";

  cv::namedWindow(title);  

  int error_code2 = glGetError();  // Error Code: 1282, GL_INVALID_OPERATION

  //cv::flip(image1, image1, 0);

  cv::imshow(title, image1);

  int error_code3 = glGetError();  // Error Code: 1282, GL_INVALID_OPERATION

  cv::waitKey(2000);

  int error_code4 = glGetError();  // Error Code: 0, NO Error

  cv::destroyWindow(title);        // IMP: however if I will comment this line then below/2nd display will work!!!

  int error_code5 = glGetError();  // Error Code: 1282, GL_INVALID_OPERATION

  image1.release();

  int error_code6 = glGetError();  // Error Code: 1282, GL_INVALID_OPERATION

  glDrawBuffer(GL_FRONT);

  int error_code7 = glGetError();// Error Code: 1282, GL_INVALID_OPERATION

  //Do it again!

  display();

  //glPushClientAttrib(GL_CLIENT_ALL_ATTRIB_BITS);

  cv::Mat image2;

  image2.create(screenHeight,screenWidth, CV_8UC3);

  glReadPixels(0, 0, screenWidth, screenHeight, GL_BGR_EXT, GL_UNSIGNED_BYTE, (uchar*)image2.data);

  int error_code8 = glGetError();  // Error Code: 0, NO Error

  //cv::flip(image2, image2, 0);

  cv::imshow(title, image2);

  cv::waitKey(5000);

   return 0;

}