float R,r,d;

float theta,dtheta;

float x,y,xo,yo;

void setup() {
  size(400,400);
  framerate(60);
  smooth();
  background(127);
  strokeWeight(7);
    
  theta = 0.0;
  dtheta = 0.2;
  
  R = 43;   // radius of outer fixed circle
  r = 15;   // radius of inner rolling circle
  d = 15;    // distance from center of rolling circle

  update_xy();
  
  theta %= TWO_PI;
}

float dr = 0.4;
float s0 = 5;
float s1 = 11;

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);
}

void draw() {
  translate(width/2,height/2);
    
  xo = x; yo = y;
  update_xy();
    
  float dx = (x-xo);
  float dy = (y-yo);
  float t = atan2(dy,dx);
  float rx = dx/cos(t);
  float ry = dy/sin(t);
  
//  println("dx:"+dx+" dy:"+dy+" t:"+t+" rx:"+rx+" ry:"+ry+
 //         " r:"+(int)r+" x:"+(int)x+" y:"+(int)y);
  
  theta += dtheta;
  //d += random(-0.5,0.5);
  r += dr; // + random(-0.2,0.2);
  
  strokeWeight(random(s0,s1));
  
  if( r> 200 ) { 
    dr = random(-0.8,-0.5); 
    stroke( 80+random(0,60),20,80+random(0,80));
    s0 = 8; s1 = 10;
   }
   if( r < 0 ) { 
     dr = random(0.6,0.8); 
     stroke( random(0,40) );
     s0 = 10; s1 = 12;
   }
 
   line( x,y, xo,yo );
   if( drawPlatelets ) {
     strokeWeight(1);
     fill(90,0,20);
     ellipse( x,y, random(20,50),random(30,40));
   }
}

boolean drawPlatelets = true;
void keyPressed() {
  drawPlatelets = !drawPlatelets;
}