//-----------------//
  // Escher's Knot   //
  // by Henry Rogers //
  // 5/4/2011 - v1.0 //
  //-----------------//
  
  // Key Controls: c - cycle; r - revolve; g - gamut; w - wireframe; mouse click drag - rotate.
  
  //---- globals
  int _e = 43;   // for elizabeth
  int _p = 576;  // number of points on curve
  int _n = 72;   // number of boxes or key frames along curve
  int _u = 8;    // number of tweens per key frame
  int _b = 4;    // number of points in width of box
  int _a = 2;    // curve scaling factor 
  
  int _c = 0;    // to cycle or not to cycle
  int _f = 0;    // frame iterator for cycling
  int _g = 0;    // to show gamut or not
  int _h = 0;    // hue interator for gamut
  int _o = 36;   // original hue for tube
  int _r = 0;    // to revolve or not to revolve
  int _m = 0;    // mobius iterator for rotation
  int _w = 0;    // to show wireframe or solids
  
  int _x = 90;   // initial x rotation
  int _y = 70;   // initial y rotation
  int _z = 90;   // initial z rotation
  int _s = 72;   // initial model scale 

  float _d1 = 0.38; // distance from corner to first midpoint on side
  float _d2 = 0.62; // distance from corner to second midpoint on side

  boolean _l = false; // lock hover state when button is pressed
    
  PImage _t; // texture image

  TrefoilCurve _k; // Trefoil knot class

  // button controls
  Button btnCycle;     // start/stop cycling
  Button btnRevolve;   // start/stop revolution
  Button btnGamut;     // show/hide gamut
  Button btnWireframe; // show/hide wireframe


  void setup()
  {
    import com.processinghacks.arcball.*;
    
    if (online==false)
    {
      import processing.opengl.*;
      size( 760, 760, OPENGL );
      smooth();
      textFont( loadFont("data/font.vlw"), 18 );
    }
    else
    {
      size( 760, 760, P3D );
      textMode(SCREEN);
    }

    colorMode( HSB, 360, 100, 100 );

    // camera control
    ArcBall arcball = new ArcBall( this );
    
    _t = loadImage( "data/lines.jpg" );
    textureMode( NORMALIZED );

    // instantiate trefoil curve
    _k = new TrefoilCurve( _a, _d1, _d2 ); 

    // instantiate button controls
    btnCycle = new Button( 6, 6, color(50,40,80), "Cycle" ); 
    btnRevolve = new Button( btnCycle.right() + 3, 6, color(50,40,80), "Revolve" );
    btnGamut = new Button( btnRevolve.right() + 3, 6, color(50,40,80), "Gamut" ); 
    btnWireframe = new Button( btnGamut.right() + 3, 6, color(50,40,80), "Wireframe" ); 
  }

  void draw()
  {
    background( 59, 7, 85 );
    lights();
    
    // adjust lighting depending on gamut or texture mode
    if ( _g == 1 )
    {
      lightSpecular( 30, 40, 50 );
      directionalLight( 0, 0, 20, 0, 0, -1 ); 
    }
    else
    {
      lightSpecular( 25, 50, 72 );
      pointLight( 25, 50, 100, 0, 0, -12 );
      directionalLight( 25, 50, 72, 0, 0, -1 );
    }
    
    translate( width/2, height/2, -height/2 );
    rotateX( radians( _x ) ); 
    rotateY( radians( _y ) );
    rotateZ( radians( _z ) );
    scale( _s );

    int i,j;
    
    // advance revolution angle by mobius iterator
    float mobius = _m * TWO_PI / (_p/6); 

    // loop through key frames on curve
    for( j=0; j<_p; j=j+_u )
    {
      i = j + _f;  // advance tube by frame iterator

      // draw sides of tube
      drawTube( i, HALF_PI * 0 + mobius );
      drawTube( i, HALF_PI * 1 + mobius );
      drawTube( i, HALF_PI * 2 + mobius );
      drawTube( i, HALF_PI * 3 + mobius );
    }
    
    // persist control iterators
    _f = ( _f + _c ) % _u;     // advance frame iterator if cycling
    _h = ( _h + _c ) % 360;    // advance hue iterator if cycling
    _m = ( _m + _r ) % (_p/6); // advance mobius iterator if revolving

    // gui io
    drawGUI();
  }