processing4/java/examples/Topics/Simulate/SmokeParticleSystem/Particle.pde

// A simple Particle class, renders the particle as an image

class Particle {
  PVector loc;
  PVector vel;
  PVector acc;
  float lifespan;
  PImage img;

  Particle(PVector l,PImage img_) {
    acc = new PVector(0,0);
    float vx = randomGaussian()*0.3;
    float vy = randomGaussian()*0.3 - 1.0;
    vel = new PVector(vx,vy);
    loc = l.get();
    lifespan = 100.0;
    img = img_;
  }

  void run() {
    update();
    render();
  }
  
  // Method to apply a force vector to the Particle object
  // Note we are ignoring "mass" here
  void applyForce(PVector f) {
    acc.add(f);
  }  

  // Method to update location
  void update() {
    vel.add(acc);
    loc.add(vel);
    lifespan -= 2.5;
    acc.mult(0); // clear Acceleration
  }

  // Method to display
  void render() {
    imageMode(CENTER);
    tint(255,lifespan);
    image(img,loc.x,loc.y);
    // Drawing a circle instead
    // fill(255,lifespan);
    // noStroke();
    // ellipse(loc.x,loc.y,img.width,img.height);
  }

  // Is the particle still useful?
  boolean isDead() {
    if (lifespan <= 0.0) {
      return true;
    } else {
      return false;
    }
  }
}