/* prac7b.c */


/* 
	Purpose:	Investigate the depth buffer 
*/

#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 Constants and Variables */

static GLfloat mNearClip = 10.0;  /* near clipping plane */
static GLfloat mFarClip  = 20.0;  /* far clipping plane */
static GLfloat mLocation = 0.0;   /* sphere location as measured from the middle of the near and far clipping planes */

void printHelp( void )
{
	fprintf(stdout,
		"\n Depth Buffer\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 ' ':
		mLocation -= 0.1;
		glutPostRedisplay();
		printf("%f\n", mLocation);
	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 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 );
}


/* Draw a grid in the XY plane */
void drawXYGrid(void)
{
	static const GLfloat max = 20;
	int i;

	glBegin(GL_LINES);
		for(i=-max; i <=max; ++i)
		{
			glVertex2f(-max, i);
			glVertex2f(max, i);
			glVertex2f(i, -max);
			glVertex2f(i, max);
		}
	glEnd();
}


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);

	glColor3f(0.0, 0.0, 1.0);
	drawXYGrid();

	glColor3f(0.0, 1.0, 1.0);
	glTranslatef(0, 0, mLocation);
	glutSolidSphere(2.0, 20, 20);

	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 );  /* Remember to call glEnable(GL_DEPTH_TEST) later */
	glutCreateWindow( argv[0] );

	init();

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


	printHelp( );

	glutMainLoop();

	return 0;
}