// This code was created by Jeff Molofee '99 (ported to Linux/GLUT by Richard Campbell '99)
//
// If you've found this code useful, please let me know.
//
// Visit me at www.demonews.com/hosted/nehe 
// (email Richard Campbell at ulmont@bellsouth.net)
//
#include <GL/glut.h>    // Header File For The GLUT Library 
#include <GL/gl.h>	// Header File For The OpenGL32 Library
#include <GL/glu.h>	// Header File For The GLu32 Library
#include <unistd.h>     // Header file for sleeping.

/* ascii code for the escape key */
#define ESCAPE 27

/* The number of our GLUT window */
int window; 

/* A general OpenGL initialization function.  Sets all of the initial parameters. */
void InitGL(int Width, int Height)	        // We call this right after our OpenGL window is created.
{
  glClearColor(0.0f, 0.0f, 0.0f, 0.0f);		// This Will Clear The Background Color To Black
  glClearDepth(1.0);				// Enables Clearing Of The Depth Buffer
  glDepthFunc(GL_LESS);				// The Type Of Depth Test To Do
  glEnable(GL_DEPTH_TEST);			// Enables Depth Testing
  glShadeModel(GL_SMOOTH);			// Enables Smooth Color Shading

  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();				// Reset The Projection Matrix

  gluPerspective(45.0f,(GLfloat)Width/(GLfloat)Height,0.1f,100.0f);	// Calculate The Aspect Ratio Of The Window

  glMatrixMode(GL_MODELVIEW);
}

/* The function called when our window is resized (which shouldn't happen, because we're fullscreen) */
void ReSizeGLScene(int Width, int Height)
{
  if (Height==0)				// Prevent A Divide By Zero If The Window Is Too Small
    Height=1;

  glViewport(0, 0, Width, Height);		// Reset The Current Viewport And Perspective Transformation

  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();

  gluPerspective(45.0f,(GLfloat)Width/(GLfloat)Height,0.1f,100.0f);
  glMatrixMode(GL_MODELVIEW);
}

/* The main drawing function. */
void DrawGLScene()
{
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);		// Clear The Screen And The Depth Buffer
  glLoadIdentity();				// Reset The View

  // since this is double buffered, swap the buffers to display what just got drawn.
  glutSwapBuffers();
}

/* The function called whenever a key is pressed. */
void keyPressed(unsigned char key, int x, int y) 
{
    /* avoid thrashing this procedure */
    usleep(100);

    /* If escape is pressed, kill everything. */
    if (key == ESCAPE) 
    { 
	/* shut down our window */
	glutDestroyWindow(window); 
	
	/* exit the program...normal termination. */
	exit(0);                   
    }
}

int main(int argc, char **argv) 
{  
  /* Initialize GLUT state - glut will take any command line arguments that pertain to it or 
     X Windows - look at its documentation at http://reality.sgi.com/mjk/spec3/spec3.html */  
  glutInit(&argc, argv);  

  /* Select type of Display mode:   
     Double buffer 
     RGBA color
     Alpha components supported 
     Depth buffer */  
  glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_ALPHA | GLUT_DEPTH);  

  /* get a 640 x 480 window */
  glutInitWindowSize(640, 480);  

  /* the window starts at the upper left corner of the screen */
  glutInitWindowPosition(0, 0);  

  /* Open a window */  
  window = glutCreateWindow("Jeff Molofee's GL Code Tutorial ... NeHe '99");  

  /* Register the function to do all our OpenGL drawing. */
  glutDisplayFunc(&DrawGLScene);  

  /* Go fullscreen.  This is as soon as possible. */
  glutFullScreen();

  /* Even if there are no events, redraw our gl scene. */
  glutIdleFunc(&DrawGLScene);

  /* Register the function called when our window is resized. */
  glutReshapeFunc(&ReSizeGLScene);

  /* Register the function called when the keyboard is pressed. */
  glutKeyboardFunc(&keyPressed);

  /* Initialize our window. */
  InitGL(640, 480);
  
  /* Start Event Processing Engine */  
  glutMainLoop();  

  return 1;
}