/* prac7d.c  */

/*
	Purpose:	Investigate the depth buffer and coplanar objects
*/

#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 */


/* Module Constants and Variables */

static const GLfloat mNearClip = 10;  /* near clipping plane */
static const GLfloat mFarClip  = 20;  /* far clipping plane */
static GLfloat mAngle = 0;   /* sphere location as measured from the middle of the near and far clipping planes */


/*
	Functions
*/

void printHelp( void )
{
	fprintf(stdout,
		"\nDepth Buffer and Coplanar Objects\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 is pressed */
		exit(0);
	break;
    case ' ':
		mAngle += 5;
		glutPostRedisplay();
	}
}


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 width, GLint height)
{
	GLdouble aspect;
	aspect = (GLdouble)width / (GLdouble)height;

	/* We still want the output to cover the whole window */
	glViewport(0, 0, width, height);

	glMatrixMode( GL_PROJECTION );
	glLoadIdentity();

	gluPerspective(50, aspect, mNearClip, mFarClip);

	glMatrixMode( GL_MODELVIEW );
}


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

	/* Do all your OpenGL rendering here */

	glLoadIdentity();   /* Reset the ModelView transformation every time we draw */

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

	glRotatef(mAngle, 0, 1, 0);

	glEnable(GL_DEPTH_TEST);
	glColor3f(0.0, 0.0, 0.0);
	glRectf(-5, -5, 5, 5);

/*	glDisable(GL_DEPTH_TEST);  */
	glColor3f(1.0, 0.0, 0.0);
	glRectf(-1, -1, 1, 1);

	checkError( "display" );

	glFlush();
}


void init( void )
{
	glClearColor( 1.0, 1.0, 1.0, 1.0);
	glColor3f(1.0,0.0,0.0);
	glLineWidth(3.0);

	glEnable(GL_DEPTH_TEST); 
}

int main( int argc, char *argv[] )
{
	glutInit( &argc, argv );

	glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH ); 
	glutCreateWindow( argv[0] );

	init();

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

	printHelp( );

	glutMainLoop();

	return 0;
}