animPoly

animatedPolygon ap1;

void setup() {
  size(500,500);
  ap1 = new animatedPolygon(4);
}

void draw() {
  background(255);
  ap1.run();
}

class animatedPolygon {

  PVector[] vertices;
  //PVector[] vertices2;
  PVector currPos;
  int counter, currentVertex=0;
  float currentPosBetweenVertices;
  float angle, cx, cy, r;
  float stepSize=.03;


  animatedPolygon(int _v) {
    vertices = new PVector[_v];
  r = 200;
    cx = width/2;
    cy = height/2;
    for (int i=0; i<vertices.length; i++) {
      float x = cx + cos(angle)*r;
      float y = cy + sin(angle)*r;
      vertices[i] = new PVector(x, y);
      angle += TWO_PI/_v;
    }
    //vertices2 = vertices.copy();
  }

  void run() {
    update();
    display();
  }

  void update() {
    if (currentVertex==vertices.length-1) {
      currPos = PVector.lerp(vertices[currentVertex], vertices[0], currentPosBetweenVertices);
    } else {
      currPos = PVector.lerp(vertices[currentVertex], vertices[currentVertex+1], currentPosBetweenVertices);
    }

    if (currentPosBetweenVertices>1) {
      currentPosBetweenVertices=0;
      if (currentVertex==vertices.length-1) {
        currentVertex=0;
        counter++;
      } else {
        currentVertex++;
      }
    }
    currentPosBetweenVertices += stepSize ;
  }

  void display() {

    stroke(0);
    for (int i=0; i<currentVertex; i++) {
      line(vertices[i].x, vertices[i].y, vertices[i+1].x, vertices[i+1].y);
    }
    line(vertices[currentVertex].x, vertices[currentVertex].y, currPos.x, currPos.y);
    /*
    stroke(255);
     for (int i=0; i<currentVertex; i++) {
     line(vertices2[i].x, vertices2[i].y, vertices2[i+1].x, vertices2[i+1].y);
     }
     line(vertices2[currentVertex].x, vertices2[currentVertex].y, currPos.x, currPos.y);
     */

    for (int i=0; i<vertices.length; i++) {
      ellipse(vertices[i].x, vertices[i].y, 10, 10);
    }
  }
}