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





#define BALL_POSITION_X 6
#define BALL_POSITION_Y -2
#define BALL_POSITION_Z 0
#define BALL_RADIUS 0.75
#define TRUE 1
#define FALSE 0




// *************************************************************************************
// * GLOBAL variables. Not ideal but necessary to get around limitatins of GLUT API... *
// *************************************************************************************
int pause = TRUE;





void init (void)
{
  glShadeModel (GL_SMOOTH);
  glClearColor (0.2f, 0.2f, 0.4f, 0.5f);				
  glClearDepth (1.0f);
  glEnable (GL_DEPTH_TEST);
  glDepthFunc (GL_LEQUAL);
  glEnable (GL_COLOR_MATERIAL);
  glHint (GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
  glEnable (GL_LIGHTING);
  glEnable (GL_LIGHT0);
  GLfloat lightPos[4] = {-1.0, 1.0, 0.5, 0.0};
  glLightfv (GL_LIGHT0, GL_POSITION, (GLfloat *) &lightPos);
  glEnable (GL_LIGHT1);
  GLfloat lightAmbient1[4] = {0.0, 0.0,  0.0, 0.0};
  GLfloat lightPos1[4]     = {1.0, 0.0, -0.2, 0.0};
  GLfloat lightDiffuse1[4] = {0.5, 0.5,  0.3, 0.0};
  glLightfv (GL_LIGHT1,GL_POSITION, (GLfloat *) &lightPos1);
  glLightfv (GL_LIGHT1,GL_AMBIENT, (GLfloat *) &lightAmbient1);
  glLightfv (GL_LIGHT1,GL_DIFFUSE, (GLfloat *) &lightDiffuse1);
  glLightModeli (GL_LIGHT_MODEL_TWO_SIDE, GL_TRUE);
}





void display (void)
{
  int x;

  glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glLoadIdentity ();
  glDisable (GL_LIGHTING);
  glBegin (GL_POLYGON);
  glColor3f (0.8f, 0.8f, 1.0f);
  glVertex3f (-200.0f, -100.0f, -100.0f);
  glVertex3f (200.0f, -100.0f, -100.0f);
  glColor3f (0.4f, 0.4f, 0.8f);	
  glVertex3f (200.0f, 100.0f, -100.0f);
  glVertex3f (-200.0f, 100.0f, -100.0f);
  glEnd ();
  glEnable (GL_LIGHTING);
  glTranslatef (-6.5, 6, -9.0f); // move camera out and center on the rope
  glPushMatrix ();
  glTranslatef (BALL_POSITION_X, BALL_POSITION_Y, BALL_POSITION_Z);
  glColor3f (1.0f, 1.0f, 0.0f);
  glutSolidSphere (BALL_RADIUS - 0.1, 50, 50); // draw the ball, but with a slightly lower radius, otherwise we could get ugly visual artifacts of rope penetrating the ball slightly
  glPopMatrix ();
  glutSwapBuffers();
  glutPostRedisplay();
}





void reshape (int w, int h)  
{
  glViewport (0, 0, w, h);
  glMatrixMode (GL_PROJECTION); 
  glLoadIdentity ();  
  if (h == 0)  
  { 
    gluPerspective (80, (float) w, 1.0, 5000.0);
  }
  else
  {
    gluPerspective (80, (float) w / (float) h, 1.0, 5000.0);
  }
  glMatrixMode (GL_MODELVIEW);  
  glLoadIdentity (); 
}





void keyboard (unsigned char key, int x, int y) 
{
  switch (key) 
  {
    case 27:    
      exit (0);
    break;  
    case 32:
      pause = 1 - pause;
      break;
    default: 
    break;
  }
}





void arrow_keys (int a_keys, int x, int y) 
{
  switch(a_keys) 
  {
    case GLUT_KEY_UP:
      glutFullScreen();
    break;
    case GLUT_KEY_DOWN: 
      glutReshapeWindow (1280, 720 );
    break;
    default:
    break;
  }
}





int main (int argc, char *argv[]) 
{
  glutInit (&argc, argv);
  glutInitDisplayMode (GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH); 
  glutInitWindowSize (1280, 720 ); 
  glutCreateWindow ("Rope simulator");
  init ();
  glutDisplayFunc (display);  
  glutReshapeFunc (reshape);
  glutKeyboardFunc (keyboard);
  glutSpecialFunc (arrow_keys);
  glutMainLoop ();
}