/*	Fly around cube on a spherical surface. Example for B481 Interactive Graphics.
	
	Ray Wisman. Indiana University Southeast. 2008
	rwisman@ius.edu

	Based on suggestions by H. Shirokawa
*/

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

GLint winWidth=600, winHeight=600;
GLfloat eyeX=0.0, eyeY=0.0, eyeZ=2.0;
GLfloat theta=270.0, phi=180.0;
GLfloat upX=0.0, upY=1.0, upZ=0.0;
GLfloat r=2.0;

static GLfloat vertices[][3]={
		{-0.5,-0.5,0.5},{-0.5,0.5,0.5},{0.5,0.5,0.5},{0.5,-0.5,0.5},
		{-0.5,-0.5,-0.5},{-0.5,0.5,-0.5},{0.5,0.5,-0.5},{0.5,-0.5,-0.5}}; 

static GLfloat colors[][3]={
		{1.0,0.0,0.0},{0.0,1.0,1.0},{1.0,1.0,0.0},
		{0.0,1.0,0.0},{0.0,0.0,1.0},{1.0,0.0,1.0}};

void polygon(int a, int b, int c, int d) {
		glColor3fv(colors[a]);
		glBegin(GL_QUADS);
			glVertex3fv(vertices[a]);
			glVertex3fv(vertices[b]);
			glVertex3fv(vertices[c]);
			glVertex3fv(vertices[d]);
		glEnd();
}

void cube() {
		polygon(0,3,2,1);
		polygon(2,3,7,6);
		polygon(3,0,4,7);
		polygon(1,2,6,5);
		polygon(4,5,6,7);
		polygon(5,4,0,1);
}

void init( void ) {
	glClearColor(1.0, 1.0, 1.0, 0.0);
	glEnable(GL_DEPTH_TEST);		
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glFrustum(-1,1,-1,1,.6,300);	
}

void displayFcn( void ) {
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glMatrixMode(GL_MODELVIEW);		// set to Model View before drawing
	glLoadIdentity();
	gluLookAt(eyeX,eyeY,eyeZ,0,0,0,upX, upY, upZ);

	glPolygonMode(GL_FRONT, GL_FILL);
	cube();

	glutSwapBuffers();
}

void reshapeFcn(GLint newWidth, GLint newHeight) {
	glViewport(0,0,newWidth, newHeight);
	winWidth=newWidth;
	winHeight=newHeight;
}

// OpenGL/GLUT C code (by H. Shirokawa)
void eyePosition( void ) {
// Spherical to Cartesian conversion.   
   eyeX = r * sin(theta*0.0174532) * sin(phi*0.0174532);
   eyeY = r * cos(theta*0.0174532);
   eyeZ = r * sin(theta*0.0174532) * cos(phi*0.0174532);
// Reduce theta slightly to obtain another point on the same longitude line on the sphere.
   GLfloat dt=1.0;
   GLfloat eyeXtemp = r * sin(theta*0.0174532-dt) * sin(phi*0.0174532);
   GLfloat eyeYtemp = r * cos(theta*0.0174532-dt);
   GLfloat eyeZtemp = r * sin(theta*0.0174532-dt) * cos(phi*0.0174532); 

   upX=eyeXtemp-eyeX;
   upY=eyeYtemp-eyeY;
   upZ=eyeZtemp-eyeZ;

   glutPostRedisplay();
}

// OpenGL/GLUT C code (by H. Shirokawa)
void onMouseMove(int x, int y) { 
// Mouse point to angle conversion
   theta = (360.0/(double)winHeight)*(double)y*3.0; //3.0 rotations possible
   phi = (360.0/(double)winWidth)*(double)x*3.0; 
// Restrict the angles within 0~360 deg (optional)
   if(theta > 360)theta = fmod((double)theta,360.0);
   if(phi > 360)phi = fmod((double)phi,360.0);
   eyePosition();
}

void SpecialKeys(int key, int x, int y) {
	if(key == GLUT_KEY_UP)		r -= 0.1;
	if(key == GLUT_KEY_DOWN)	r += 0.1;

	eyePosition();
}

void main(int argc, char** argv) {
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
	glutInitWindowPosition(50,50);
	glutInitWindowSize(winWidth,winHeight);
	glutCreateWindow("Cube");

	init();
	glutDisplayFunc(displayFcn);
	glutReshapeFunc(reshapeFcn);
	glutPassiveMotionFunc(onMouseMove);
	glutSpecialFunc(SpecialKeys);
	printf("Fly Around an Object on a Spherical Surface\n\nMouse moves eye position.\nUp/Down arrow change radius of sphere.");
	glutMainLoop();
}