#include<GL/glut.h>
#include<GL/glu.h>
#include<GL/gl.h>

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();

	// Translate the whole scene out and into view	
	glTranslatef(0.0f, 0.0f, -300.0f);	
	
	// Sun
	glColor3ub(255, 255, 0);
	glutSolidSphere(15.0f, 30, 17);
	
	// Rotate coordinate system
	glRotatef(fEarthRot, 0.0f, 1.0f, 0.0f);

	// Draw the Earth
	glColor3ub(0,0,255);
	glTranslatef(105.0f,0.0f,0.0f);
	glutSolidSphere(15.0f, 30, 17);

	// 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);
	glutSolidSphere(6.0f, 30, 17);

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

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

        fMoonRot+= 15.0f;
        if(fMoonRot > 360.0f)
		fMoonRot = 0.0f;
	// Show the image
	glutSwapBuffers();
	}


// This function does any needed initialization on 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);		// Do not calculate inside 
	// Black blue background
	glClearColor(0.0f, 0.0f, 0.0f, 1.0f );
    }


void TimerFunc(int value)
    {
    glutPostRedisplay();
    glutTimerFunc(100, TimerFunc, 1);
    }

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);
        glutInitWindowSize(800, 600);
	glutCreateWindow("Earth/Moon/Sun System");
	glutReshapeFunc(ChangeSize);
	glutDisplayFunc(RenderScene);
        glutTimerFunc(100, TimerFunc, 1);
	SetupRC();
	glutMainLoop();
	return 0;
	}