/*
 *  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);
   glColor3f(1.0, 1.0, 1.0);

   glPushMatrix();
   glutWireSphere(1.0, 20, 16);   /* draw sun */
   glRotatef((GLfloat)year, 0.0, 1.0, 0.0);
   glTranslatef(2.0, 0.0, 0.0);
   glRotatef((GLfloat)day, 0.0, 1.0, 0.0);
   glutWireSphere(0.2, 10, 8);    /* draw smaller planet */
   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);
}

/* ARGSUSED1 */
void keyboard (unsigned char key, int x, int y)
{
   switch (key) {
      case 'd':
         day = (day + 10) % 360;
         glutPostRedisplay();
         break;
      case 'D':
         day = (day - 10) % 360;
         glutPostRedisplay();
         break;
      case 'y':
         year = (year + 5) % 360;
         glutPostRedisplay();
         break;
      case 'Y':
         year = (year - 5) % 360;
         glutPostRedisplay();
         break;
      case 27:
         exit(0);
         break;
      default:
         break;
   }
}

int main(int argc, char **argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
   glutInitWindowSize(500, 500); 
   glutInitWindowPosition(100, 100);
   glutCreateWindow(argv[0]);
   init();
   glutDisplayFunc(display); 
   glutReshapeFunc(reshape);
   glutKeyboardFunc(keyboard);
   glutMainLoop();
   return 0;
}