Cardioid via epicycloid with one cusp

/*

  1. Draw a circle

  2. Draw a point D*cos(angle), D*sin(angle) away from the centre

*/

float D, r, angle, rate;

ArrayList<PVector> points;

​

void setup(){

  //strokeWeight(2);

  size(screenWidth,screenHeight);

  noFill();

  points = new ArrayList<PVector>();

  D = screenHeight*.30;

  r = D/2;

  angle = 0;

  rate = 0.02;

}

​

void draw(){

  background(0);

  stroke(255,100);

  strokeWeight(2);

  pushMatrix();

    translate(width/2, height/2);

    ellipse(0,0, D, D);

    PVector loc = new PVector(D*cos(angle), D*sin(angle));

​

    point(loc.x, loc.y);

   // pushMatrix();

   //   translate(loc.x, loc.y);

      //ellipse(0,0,D,D);

​

       ellipse(loc.x,loc.y,D,D);

      float x = loc.x+r*cos(2*angle-PI);

      float y = loc.y+r*sin(2*angle-PI);

      //line(0,0,x,y);

      line(loc.x, loc.y,x,y);

      stroke(255,0,0);

      strokeWeight(5);

      point(x,y);

      //add a point to the array list every second frame if we haven't already gone around

      //if (angle < TWO_PI & frameCount%2 == 0){

      //  points.add(new PVector(x,y));       

      //}

      if (angle < TWO_PI){

        points.add(new PVector(x,y));       

      }

      //point(x,y);

   // popMatrix();

  popMatrix();

  angle += rate;

  draw_cardioid(); 

}

​

void draw_cardioid(){

  stroke(255);

  strokeWeight(2);

  pushMatrix();

  translate(width/2,height/2);

    beginShape();

            for(PVector pt : points){

              vertex(pt.x, pt.y);

            }

  endShape();

  popMatrix();

}