/*
 *  planet.c
 *  This program shows how to composite modeling transformations
 *  to draw translated and rotated models.
 *  Interaction:  pressing the d and y keys (day and year)
 *  alters the rotation of the planet around the sun.
 */
#include <GL/glut.h>
#include <stdlib.h>

static int year = 0, day = 0;

void init(void) 
{
   glClearColor (0.0, 0.0, 0.0, 0.0);
   glShadeModel (GL_FLAT);
}

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

   glPushMatrix();
     glColor3f (1.0, 1.0, 0.0);
     glutSolidSphere(1.0, 20, 16);   /* draw sun */
     glPushMatrix();
       glRotatef ((GLfloat)(year%360), 0.0, 1.0, 0.0);
       glTranslatef (2.0, 0.0, 0.0);
       glRotatef ((GLfloat)(day%360), 0.0, 1.0, 0.0);
       glColor3f (0.0, 0.0, 1.0);
       glutSolidSphere(0.2, 10, 8);    /* draw blue planet */
     glPopMatrix();
     glPushMatrix();
       glRotatef ((GLfloat)((year/2)%360), 0.0, 1.0, 0.0);
       glTranslatef (2.5, 0.0, 0.0);
       glRotatef ((GLfloat)((day/2)%360), 0.0, 1.0, 0.0);
       glColor3f (1.0, 0.0, 0.0);
       glutSolidSphere(0.15, 10, 8);    /* draw red planet */
     glPopMatrix();
   glPopMatrix();
   glutSwapBuffers();
}

void reshape (int w, int h)
{
   glViewport (0, 0, (GLsizei) w, (GLsizei) h); 
   glMatrixMode (GL_PROJECTION);
   glLoadIdentity ();
   gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
   gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
   glEnable(GL_DEPTH_TEST);
}

void keyboard (unsigned char key, int x, int y)
{
   switch (key) {
      case 'd':
         day = (day + 10);
         glutPostRedisplay();
         break;
      case 'D':
         day = (day - 10);
         glutPostRedisplay();
         break;
      case 'y':
         year = (year + 5);
         glutPostRedisplay();
         break;
      case 'Y':
         year = (year - 5);
         glutPostRedisplay();
         break;
      case 27:
         exit(0);
         break;
      default:
         break;
   }
}

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
   glutInitWindowSize (600, 400); 
   glutInitWindowPosition (100, 100);
   glutCreateWindow (argv[0]);
   init ();
   glutDisplayFunc(display); 
   glutReshapeFunc(reshape);
   glutKeyboardFunc(keyboard);
   glutMainLoop();
   return 0;
}