float R,r,d;
float theta,dtheta;
float x,y,xo,yo;
float dr;
float sc;  // scale
PFont fontA;

void setup() {
  size(400,400);
  framerate(60);
  background(127);
  strokeWeight(7);
  fontA = loadFont("CourierNewPSMT-9.vlw");
  textFont(fontA, 12);
  smooth();
  
  theta = 0.0;
  dtheta = 0.2;
  
  R = 110;   // radius of outer fixed circle
  r = 64;   // radius of inner rolling circle
  d = 90;    // distance from center of rolling circle
  dr = 0.4;
  sc = 1;
  update_xy();
  
}

void update_xy() {
  x = (R-r)*cos(theta) + d*cos( ((R-r)/r)*theta );
  y = (R-r)*sin(theta) - d*sin( ((R-r)/r)*theta );
  //x = r * cos(theta);
  //y = r * sin(theta);
  
  theta += dtheta;
  //   r += dr; // + random(-0.2,0.2);
  //  if( r> 200 )  dr = random(-0.6,-0.5); 
  //  if( r < 0 )   dr = random(0.6,0.8);
}

void draw() {
  fill(127); stroke(127);
  rect(0,0,width,16);
  fill(0);
  text("R:"+(int)R+" r:"+(int)r+" d:"+(int)d+" theta:"+(int)theta,8,8);
  text("space randoms, return clears, +/- scales, [],<> alters", 8,16);
  pushMatrix();
  smooth();
  translate(width/2,height/2);
  scale(sc);
    
  xo = x; yo = y;
  update_xy();
    
  float dx = (x-xo);
  float dy = (y-yo);
  float rth = atan2(dy,dx);
  float rx = (dx/cos(rth))/dtheta;
  float ry = (dy/sin(rth))/dtheta;
  
//  println("dx:"+dx+" dy:"+dy+" rth:"+rth+" rx:"+rx+" ry:"+ry+
//          " r:"+(int)r+" x:"+(int)x+" y:"+(int)y);
 
  stroke( 0,0, 100-100*cos(theta/100) ); // this is clever i thought
  strokeWeight(5);
  line( x,y, xo,yo);

 // stroke(1); noFill(); strokeWeight(1);
 // ellipse(0,0, R,R);
 // ellipse( (R-r)*sin(theta), (R-r)*cos(theta), r,r);
  
  popMatrix();  
}

void keyPressed() {
  if( key == CODED ) {
    if( keyCode == UP )
      d += 1;
    else if( keyCode == DOWN )
      d -= 1;
    else if( keyCode == LEFT )
      r += 1;
    else if( keyCode == RIGHT )
      r -= 1;
  }
  else if( keyCode == RETURN || keyCode == ENTER )
    background(127);
  else {
    if( key == ',' || key == '<' )
      R -= 5;
    else if( key == '.' || key == '>' ) 
      R += 5;
    else if( key == ']' )
      dtheta += 0.01;
    else if( key == '[' )
      dtheta -= 0.01;
    else if( key == '-' || key == '_' ) 
      sc -= 0.1;
    else if( key == '=' || key == '+' )
      sc += 0.1;
    else if( key == ' ' ) {
      d = random( 10,100);
      R = random( 100,140);
      d = random( 10,100);
      theta = 0;
      update_xy();
      xo = x; yo = y;
      background(127);
    } 
  }  
}