processing4/java/examples/Books/Nature of Code/chp3_oscillation/AttractionArrayWithOscillation/Crawler.pde

// Attraction
// Daniel Shiffman <http://www.shiffman.net>
// Nature of Code, Spring 2012

// A class to describe a thing in our world, has vectors for location, velocity, and acceleration
// Also includes scalar values for mass, maximum velocity, and elasticity

class Crawler {
  PVector loc;
  PVector vel;
  PVector acc;
  float mass;
  
  Oscillator osc;
    
  Crawler() {
    acc = new PVector();
    vel = new PVector(random(-1,1),random(-1,1));
    loc = new PVector(random(width),random(height));
    mass = random(8,16);
    osc = new Oscillator(mass*2);
  }
  
  void applyForce(PVector force) {
    PVector f = force.get();  
    f.div(mass);
    acc.add(f);
  }

  // Method to update location
  void update() {
    vel.add(acc);
    loc.add(vel);
    // Multiplying by 0 sets the all the components to 0
    acc.mult(0);
    
    osc.update(vel.mag()/10);
  }
  
  // Method to display
  void display() {
    float angle = vel.heading2D();
    pushMatrix();
    translate(loc.x,loc.y);
    rotate(angle);
    ellipseMode(CENTER);
    stroke(0);
    fill(175,100);
    ellipse(0,0,mass*2,mass*2);
    
    osc.display(loc);
    popMatrix();
    
  }
}