float R,r,d;

float theta,dtheta;

float x,y,xo,yo;

void setup() {
  size(400,400);
  framerate(60);
  smooth();
  background(127);
  strokeWeight(3);
    
  theta = 0.0;
  dtheta = 0.1;
  
  R = 43;   // radius of outer fixed circle
  r = 13;   // radius of inner rolling circle
  d = 15;    // distance from center of rolling circle

  x = (R-r)*cos(theta) + d*cos( ((R-r)/r)*theta );
  y = (R-r)*sin(theta) - d*sin( ((R-r)/r)*theta );

  theta %= TWO_PI;
}


void draw() {
  translate(width/2,height/2);
  scale(3.0);
  stroke(200-(theta%100),0, 127 + (theta % 127));
    
  xo = x; yo = y;
  x = (R-r)*cos(theta) + d*cos( ((R-r)/r)*theta );
  y = (R-r)*sin(theta) - d*sin( ((R-r)/r)*theta );
  
  line( x,y, xo,yo );
  
//  println("dx:"+(x-xo)+", dy:"+(y-yo));
  
  theta += dtheta;
  d += random(-0.5,0.5);
}