/*****************************
 view3d.c

This file demonstrates 3D viewing
of a teapot with openGL.
*******************************/

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <GLUT/glut.h>

#define TRANSLATE 1
#define QUIT 2

float translate = 0.0;
float current_translation = 0.0;

/*
*	renderPerspective
*	This function renders a 3D perspective image
*	of the Utah Teapot.
*/

void renderPerspective()
{
	glClear(GL_COLOR_BUFFER_BIT);
	glLoadIdentity();

	current_translation += translate;
        
	/* NOTE: this only works for situations where the DoP is */
	/* orthogonal to the viewplane */
        //glTranslatef(current_translation, 0.0, 0.0);
        gluLookAt(5+current_translation, 5, 5, current_translation, 0, 0, 0, 1, 0);
        //glTranslatef(current_translation, 0.0, 0.0);
        
        if(current_translation >= 3.0 || current_translation <= -3.0)
            translate = -translate;

	glutWireTeapot(2);

	glutSwapBuffers();
	glutPostRedisplay();
}

/*
* reshape
* This is the reshape callback function, which sets up
* the window->viewport transformation and the perspective
* projection transformation.
*/

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

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

        gluPerspective(60.0, 1.0, 1.0, 100.0);
	glMatrixMode(GL_MODELVIEW);
}

/*
* menu_callback: the callback function when a menu item
* is selected. Just a big switch statement with an entry
* for each menu item.
*/

void menu_callback(int value)
{
	switch(value){
        case TRANSLATE:
                if(translate == 0.0) translate = 0.1;
                else translate = 0.0;
                break;
	case QUIT:
		glutDestroyWindow(glutGetWindow());
		exit(0);
		break;
	default:
		break;
	}
}

/*
* init_menus: subroutine to set up the pop-up menu
* for this program
*/

void init_menus()
{
	int my_menu;

	// create a menu and set callback fn.
	my_menu = glutCreateMenu(menu_callback);
	
	// insert the menu items in order
        glutAddMenuEntry("Toggle camera movement", TRANSLATE);
	glutAddMenuEntry("Quit", QUIT);
	
	// use the right mouse button to call up the menu
	glutAttachMenu(GLUT_RIGHT_BUTTON);
}

/*
*	Main function.  Reads in the polygon and viewing information,
*	places it in data structures, and creates an interface window.
*/

void main(int argc, char **argv)
{
	/* initialize */
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);

	/* create the interface window */
	glutInitWindowSize(300, 300);
	glutInitWindowPosition(0, 0);
	glutCreateWindow("3D Perspective Teapot");

	/* set the reshape and display functions */
	glutReshapeFunc(reshape);
	glutDisplayFunc(renderPerspective);

	init_menus();

	/* enter the main loop */
	glutMainLoop();
}