// This program illustrates both lighting and
// relative movement (moon around earth and earth around sun

#include "stdafx.h"

#using <mscorlib.dll>

using namespace System;


#include <glut.h>
#include <math.h>


// Lighting values
GLfloat  whiteLight[] = { 0.2f, 0.2f, 0.2f, 1.0f };
GLfloat  sourceLight[] = { 0.8f, 0.8f, 0.8f, 1.0f };
GLfloat	 lightPos[] = { 0.0f, 0.0f, 0.0f, 1.0f };


// Called to draw scene
void RenderScene(void)
	{
	// Earth and Moon angle of revolution
	static float fMoonRot = 0.0f;
	static float fEarthRot = 0.0f;

	// Clear the window with current clearing color
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	// Save the matrix state and do the rotations
	glMatrixMode(GL_MODELVIEW);
	glPushMatrix();

	// Set light position before viewing transformation
	glLightfv(GL_LIGHT0,GL_POSITION,lightPos);

	// Translate the whole scene out and into view	
	glTranslatef(0.0f, 0.0f, -300.0f);	
	
	// Set material color, Red
	// Sun
	glColor3ub(255, 255, 0);
	glutSolidSphere(15.0f, 15, 15);//draws a sphere with radius 15.
	//the smoothness of the sphere depends on the number of subdivisions
	//around and along the z axis, the other parameters.

	// Move the light after we draw the sun!
	glLightfv(GL_LIGHT0,GL_POSITION,lightPos);

	// Rotate coordinate system
	glRotatef(fEarthRot, 0.0f, 1.0f, 0.0f);//around y axis, the vector
	//formed by joining the point (0,1,0) to the origin.

	// Draw the Earth
	glColor3ub(0,0,255);
	glTranslatef(105.0f,0.0f,0.0f);
	glutSolidSphere(15.0f, 15, 15);


	// Rotate from Earth based coordinates and draw Moon
	glColor3ub(200,200,200);
	glRotatef(fMoonRot,0.0f, 1.0f, 0.0f);
	glTranslatef(30.0f, 0.0f, 0.0f);
	fMoonRot+= 15.0f;
	if(fMoonRot > 360.0f)
		fMoonRot = 0.0f;//keep angle of rotation under 360

	glutSolidSphere(6.0f, 15, 15);

	// Restore the matrix state
	glPopMatrix();	// Modelview matrix


	// Step earth orbit 5 degrees
	fEarthRot += 5.0f;
	if(fEarthRot > 360.0f)
		fEarthRot = 0.0f;

	// Show the image
	glutSwapBuffers();
	}


// This function does any needed initialization for the rendering
// context. 
void SetupRC()
	{
	// Light values and coordinates
	glEnable(GL_DEPTH_TEST);	// Hidden surface removal
	glFrontFace(GL_CCW);		// Counter clock-wise polygons face out
	glEnable(GL_CULL_FACE);		// hide back faces

	// Enable lighting
	glEnable(GL_LIGHTING);

	// Setup and enable light 0
	glLightModelfv(GL_LIGHT_MODEL_AMBIENT,whiteLight);
	glLightfv(GL_LIGHT0,GL_DIFFUSE,sourceLight);
	glLightfv(GL_LIGHT0,GL_POSITION,lightPos);
	glEnable(GL_LIGHT0);//tell openGL to use material properties and 
	//lighting parameters in determining the color for each
	//vertex in the scene.  If no material properties are secified,
	//the scene will remain dark.

	// Enable color tracking
	glEnable(GL_COLOR_MATERIAL);//This tells openGL that a function
	//called glColorMaterial will specify the material
	//parameters that follow the values set by glColor
	
	// Set Material properties to follow glColor values
	glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE);

	// Black  background
	glClearColor(0.0f, 0.0f, 0.0f, 1.0f );
    }


void TimerFunc(int value)
    {
    glutPostRedisplay();
    glutTimerFunc(100, TimerFunc, 1);//keep the solar system
	//from spinning too fast
    }

void ChangeSize(int w, int h)
	{
	GLfloat fAspect;

	// Prevent a divide by zero
	if(h == 0)
		h = 1;

	// Set Viewport to window dimensions
    glViewport(0, 0, w, h);

	// Calculate aspect ratio of the window
	fAspect = (GLfloat)w/(GLfloat)h;

	// Set the perspective coordinate system
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

	// field of view of 45 degrees, near and far planes 1.0 and 425
	gluPerspective(45.0f, fAspect, 1.0, 425.0);

	// Modelview matrix reset
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
   	}


int main(int argc, char* argv[])
	{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
	glutCreateWindow("Earth/Moon/Sun System");
	glutReshapeFunc(ChangeSize);
	glutDisplayFunc(RenderScene);
    glutTimerFunc(500, TimerFunc, 1);
	SetupRC();
	glutMainLoop();

	return 0;
	}