/* prac8a.c   */

/*
	Purpose:  Exploring gluLookAt
*/

#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif

#include <stdlib.h>
#include <stdio.h>

#define KEY_ESC 27      /* glut doesn't define this one */


/* Global Variables */

static const GLfloat mNearClip = 5.0;  /* near clipping plane */
static const GLfloat mFarClip  = 15.0;  /* far clipping plane */

void printHelp( void )
{
	fprintf(stdout,
		"\n Exploring gluLookAt\n\n"
		"Escape key - exit the program\n\n");
}

GLvoid keyboard (GLubyte key, GLint x, GLint y)
{ 
	switch(key)
	{
	case KEY_ESC:      /* exit when escape key pressed  */
		exit (0);
	break;

	default :
		break ;
	}
}

GLvoid specialkeys( GLint key, GLint x, GLint y)
{
    switch (key) 
	{
    	case GLUT_KEY_F1:   /* print Help information */
        	printHelp ( );
	    break;
    }
}

GLvoid checkError( const char* const label )
{
	GLenum error;

	error = glGetError();
	while ( GL_NO_ERROR != error )
	{
		fprintf( stderr,"%s: %s\n", label, gluErrorString(error) );
		error = glGetError();
	}
}

void reshape (GLint w, GLint h)
{
	if (w >= h)
	{
		glViewport(0, 0, h, h);
	}
	else
	{
		glViewport(0, 0, w, w);
	}

	glMatrixMode (GL_PROJECTION);
	glLoadIdentity ();
	gluPerspective (30, 1.0, mNearClip, mFarClip);
	glMatrixMode (GL_MODELVIEW);
	glLoadIdentity ();

}

/* Displays 6 faces of a cube  */

void drawModel (void)
{
	glBegin(GL_QUADS);
		glColor4f(0.0,0.0,1.0,1.0);
		glVertex3f(-0.5,-0.5,0.5);
		glVertex3f(0.5,-0.5,0.5);
		glVertex3f(0.5,0.5,0.5);
		glVertex3f(-0.5,0.5,0.5);
	glEnd();

	glBegin(GL_QUADS);
		glColor4f(1.0,0.0,0.0,1.0);
		glVertex3f(0.5,-0.5,0.5);
		glVertex3f(0.5,-0.5,-0.5); 
		glVertex3f(0.5,0.5,-0.5);
		glVertex3f(0.5,0.5,0.5);
	glEnd(); 

	glBegin(GL_QUADS);
		glColor4f(1.0,1.0,0.0,1.0);
		glVertex3f(0.5,-0.5,-0.5);  
		glVertex3f(-0.5,-0.5,-0.5); 
		glVertex3f(-0.5,0.5,-0.5);
		glVertex3f(0.5,0.5,-0.5);
	glEnd();

	glBegin(GL_QUADS);
		glColor4f(0.0,1.0,0.0,1.0);
		glVertex3f(-0.5,-0.5,-0.5);
		glVertex3f(-0.5,-0.5,0.5);
		glVertex3f(-0.5,0.5,0.5);
		glVertex3f(-0.5,0.5,-0.5);
	glEnd();

	glBegin(GL_QUADS);
		glColor4f(1.0,0.0,1.0,1.0);
		glVertex3f(-0.5,-0.5,-0.5);
		glVertex3f(0.5,-0.5,-0.5);
		glVertex3f(0.5,-0.5,0.5);
		glVertex3f(-0.5,-0.5,0.5);
	glEnd();

	glBegin(GL_QUADS);
		glColor4f(0.0,1.0,1.0,1.0);
		glVertex3f(-0.5,0.5,0.5);
		glVertex3f(0.5,0.5,0.5);
		glVertex3f(0.5,0.5,-0.5);
		glVertex3f(-0.5,0.5,-0.5);
	glEnd();

} 


GLvoid init(GLvoid)
{
	glClearColor(0.0, 0.0, 0.0, 0.0);
	glShadeModel(GL_FLAT);
	glEnable(GL_DEPTH_TEST);

	glEnable (GL_CULL_FACE);
	glCullFace(GL_BACK);
}


GLvoid display(GLvoid)
{
	glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	/* Translate our origin to midway between the near and far clipping plane */
	glTranslatef(0, 0, -(mNearClip+mFarClip)/2);

	/* Change the values of gluLookat to figure out what it does! :) */
	gluLookAt( 1.2,-2,-3, /* camera position      */ 
		       0,0,0,     /* centre of view       */
			   0,1,0);    /* what direction is up */

	drawModel ();

	glFlush();
}


int main(int argc, char** argv)
{
	glutInit (&argc, argv) ;
	glutInitDisplayMode ( GLUT_RGB | GLUT_DEPTH ) ;

	glutCreateWindow( argv[0] );

	init();

	glutDisplayFunc (display) ;
	glutKeyboardFunc(keyboard) ;
	glutSpecialFunc (specialkeys);
	glutReshapeFunc (reshape);

	printHelp( );

	glutMainLoop() ;

return 0 ;
}