Cardioid via envelope of circles

float D, r, theta, rate;

ArrayList<PVector> drawme;

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void setup(){

  size(screenWidth, screenHeight);

  D = screenHeight*.3;

  r = D/2;

  theta = -HALF_PI;

  rate = TWO_PI/1000;

  drawme = new ArrayList<PVector>();

  noFill();

​

}

​

void draw(){

  background(0);

  pushMatrix();

    translate(width/2, height/2-r);

    stroke(255);

    strokeWeight(2);

    ellipse(0,0,D,D);

    PVector centre = new PVector(r*cos(theta), r*sin(theta));

    PVector anchor = new PVector(0,-r);

    float radius = PVector.sub(centre, anchor).mag();

    ellipse(centre.x, centre.y, 2*radius,2*radius);

    //if(frameCount%10 == 0){

    //  ellipse(centre.x, centre.y, 2*radius,2*radius);

    //}

    //store the centrepoint and the radius inside a 3D vector

    //also, stop adding new circles to draw once we get all the way around i.e. to TWO_PI - HALF_PI

    if(frameCount%10 == 0 & theta < TWO_PI-HALF_PI){

      drawme.add(new PVector(centre.x,centre.y,2*radius));

    //  ellipse(centre.x, centre.y, 2*radius,2*radius);

    }

    strokeWeight(5);

    point(centre.x, centre.y);

  popMatrix();

  theta += rate;

  drawCircles();

}

​

void drawCircles(){

  // draw each circle using x, y (centre points) and z: diameter)

  strokeWeight(1);

  stroke(255,100);

  pushMatrix();

  translate(width/2, height/2-r);

  for (PVector thing : drawme){

    ellipse(thing.x,thing.y,thing.z, thing.z);

  }

  popMatrix();

}