The Nature of Code - Exercise 2.3

Exercise2_3.pde

Mover[] movers = new Mover[4];

void setup() {
  size(800, 320);

  for (int i = 0; i < movers.length; i++) {
    movers[i] = new Mover(random(0.1, 5), random(0, width), random(0, height));
  }
}

void draw() {
  background(255);

  PVector wind = new PVector(0.01, 0);
  PVector gravity = new PVector(0, 0.1);

  for (int i = 0; i < movers.length; i++) {
    Mover m = movers[i];
    float edgeForceScale = 0.0002;

    PVector leftForce = new PVector(abs(width - m.location.x) * edgeForceScale, 0);
    PVector rightForce = new PVector(-(m.location.x * edgeForceScale), 0);
    PVector topForce = new PVector(0, abs(height - m.location.y) * edgeForceScale);
    PVector bottomForce = new PVector(0, -(m.location.y * edgeForceScale));

    movers[i].applyForce(leftForce);
    movers[i].applyForce(rightForce);
    movers[i].applyForce(topForce);
    movers[i].applyForce(bottomForce);

    movers[i].applyForce(wind);
    movers[i].applyForce(gravity);

    movers[i].update();
    movers[i].display();
  }
}

Mover.pde

class Mover {
  PVector location;
  PVector velocity;
  PVector acceleration;
  float mass;

  Mover(float m, float x, float y) {
    mass = m;
    location = new PVector(x, y);
    velocity = new PVector(0, 0);
    acceleration = new PVector(0, 0);
  }

  void applyForce(PVector force) {
    PVector f = PVector.div(force, mass);
    acceleration.add(f);
  }

  void update() {
    velocity.add(acceleration);
    location.add(velocity);
    acceleration.mult(0);
  }

  void display() {
    stroke(0);
    fill(128, 198);
    ellipse(location.x, location.y, mass*16, mass*16);
  }
}