// 
// Torbert, 3.12.2009
// 
// OpenGL Demo, 3-D Example
// 

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>
#include <GL/glut.h>

///////////////////////////////
double pi=3.1415926;

int    w=640,h=480;

double rho,phi,theta,up=1.0;
double xc,yc,zc,xe,ye,ze;
///////////////////////////////

void display(void)
{
   double t;

   glClear(GL_COLOR_BUFFER_BIT); // clear the screen
   glColor3f(0.0,0.0,0.0);

   glutWireTeapot(1.0);

   glutSwapBuffers();
}
void look()
{
	xe=xc+rho*sin(theta)*sin(phi); // y
	ye=yc+rho*cos(theta);          // z
	ze=zc+rho*sin(theta)*cos(phi); // x
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
	gluLookAt(xe,ye,ze, xc,yc,zc, 0.0,up,0.0);
}
void idle(void)
{
	if(up>0.0)
	{
		if(theta+0.001>pi)
		{
			up*=-1.0;
			theta=-pi;
		}
	}
	else if(theta+0.001>0.0)
			up*=-1.0;
	theta+=0.001;

//	phi+=0.01;
//	rho+=0.005;

	look();
	glutPostRedisplay();
}
void mouse(int button,int state,int xscr,int yscr)
{
}
void motion(int xscr,int yscr)
{
}
void mouse_wheel(int wheel,int direction,int xscr,int yscr)
{
}
void keyfunc(unsigned char key,int xscr,int yscr)
{
	if(key=='q')
	{
		exit(0);
	}
}
void reshape(int wscr,int hscr)
{
	GLfloat aspect_ratio;

	w=wscr;
	h=hscr;
	aspect_ratio=(GLfloat)w/(GLfloat)h;
   glViewport(0,0,(GLsizei)w,(GLsizei)h);

   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
	gluPerspective(60.0,aspect_ratio,0.1,500.0);

	look();
}
int main(int argc,char* argv[])
{  
	rho=3.1;
	phi=0.0;
	theta=pi/2.0;
	xc=yc=zc=0.0;

   glutInit(&argc,argv);
   glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
   glutInitWindowSize(w,h);
   glutInitWindowPosition(100,50);
   glutCreateWindow("OpenGL Demo");

   glClearColor(1.0,1.0,1.0,0.0);
	glShadeModel(GL_SMOOTH);

   glutDisplayFunc(display);
	glutIdleFunc(idle);
   glutMouseFunc(mouse);
   glutMotionFunc(motion);
   glutMouseWheelFunc(mouse_wheel);
	glutKeyboardFunc(keyfunc);
	glutReshapeFunc(reshape);

   glutMainLoop();

   return 0;
}