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//*************************************************************************
//
//  File Name   : PixGen.c
//  Author      : Ali BaderEddin
//  Created     : December 2003
//  Modified    : March 2010
//
//  Description : Generate new image with random colors on mouse click.
//
//*************************************************************************

#include <stdlib.h>
#include <time.h>
#include <gl/glut.h>

//  Avoid showing up the console window
#pragma comment(linker,"/subsystem:\"windows\" /entry:\"mainCRTStartup\"")

//  constants representing the window size
#define WINDOW_WIDTH 512
#define WINDOW_HEIGHT 512

//  Initialization
void init ();

//  Callback functions
void display (void);
void mouse (int button, int state, int x, int y);
void keyboard (unsigned char key, int x, int y);

//  Support Functions
void centerOnScreen ();

//  define the window position on screen
int window_x;
int window_y;

//  variable representing the window title
char *window_title = "Image Generator";

//  Tells whether to display the window full screen or not
//  Press Alt + Esc to exit a full screen.
int full_screen = 0;

//  Generates a random image...
void generateImage ();

//  Represents the pixel buffer in memory
GLubyte buffer[WINDOW_WIDTH][WINDOW_HEIGHT][3];

//-------------------------------------------------------------------------
//  Set OpenGL program initial state.
//-------------------------------------------------------------------------
void init ()
{
    glClearColor (0.0, 0.0, 0.0, 0.0);
    glShadeModel(GL_FLAT);
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    srand (time(NULL));
    generateImage();
}

//-------------------------------------------------------------------------
//  This function is passed to glutDisplayFunc in order to display
//  OpenGL contents on the window.
//-------------------------------------------------------------------------
void display (void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glDrawPixels(WINDOW_WIDTH, WINDOW_HEIGHT, GL_RGB,
                    GL_UNSIGNED_BYTE, buffer);
    glutSwapBuffers ();
}

//-------------------------------------------------------------------------
//  This function is passed to the glutMouseFunc and is called
//  whenever the mouse is clicked.
//-------------------------------------------------------------------------
void mouse (int button, int state, int x, int y)
{
    if (state == GLUT_DOWN)
    {
        generateImage ();
        glutPostRedisplay ();
    }
}

//-------------------------------------------------------------------------
//  This function is passed to the glutKeyboardFunc and is called
//  whenever the user hits a key.
//-------------------------------------------------------------------------
void keyboard (unsigned char key, int x, int y)
{
    switch (key)
    {
        case 'g':
            generateImage ();
            glutPostRedisplay ();
            break;
        case 27:
            exit (0);
    }
}

//-------------------------------------------------------------------------
//  This function sets the window x and y coordinates
//  such that the window becomes centered
//-------------------------------------------------------------------------
void centerOnScreen ()
{
    window_x = (glutGet (GLUT_SCREEN_WIDTH) - WINDOW_WIDTH)/2;
    window_y = (glutGet (GLUT_SCREEN_HEIGHT) - WINDOW_HEIGHT)/2;
}

//-------------------------------------------------------------------------
//  Generate new image with random colors
//-------------------------------------------------------------------------
void generateImage ()
{
    int i, j;

    for (i = 0; i < WINDOW_WIDTH; i++)
    {
        for (j = 0; j < WINDOW_HEIGHT; j++)
        {
            buffer[i][j][0] = (GLubyte) (rand () % 256);
            buffer[i][j][1] = (GLubyte) (rand () % 256);
            buffer[i][j][2] = (GLubyte) (rand () % 256);
        }
    }
}

//-------------------------------------------------------------------------
//  Program Main method.
//-------------------------------------------------------------------------
void main (int argc, char **argv)
{
    //  Connect to the windowing system
    glutInit(&argc, argv);

    //  create a window with the specified dimensions
    glutInitWindowSize (WINDOW_WIDTH, WINDOW_HEIGHT);

    //  Set the window x and y coordinates such that the
    //  window becomes centered
    centerOnScreen ();

    //  Position Window
    glutInitWindowPosition (window_x, window_y);

    //  Set Display mode
    glutInitDisplayMode (GLUT_RGB | GLUT_DOUBLE);

    //  Create window with the specified title
    glutCreateWindow (window_title);

    //  View in full screen if the full_screen flag is on
    if (full_screen)
        glutFullScreen ();

    //  Set OpenGL program initial state.
    init();

    // Set the callback functions
    glutDisplayFunc (display);
    glutKeyboardFunc (keyboard);
    glutMouseFunc (mouse);

    //  Start GLUT event processing loop
    glutMainLoop();
}