// We only need a single particle system
ParticleSystem ps;

void setup() {
    
    // setup the environment
    size(400, 400);
    colorMode(RGB, 255, 255, 255, 100);
    smooth();
    
    // To create our particle system we use two properties:
    //    1 -> How many particles should we start with
    //    Vector3D -> What is the origin of the particle system
    ps = new ParticleSystem(1, new Vector3D(width / 2, height / 2, 0));
}

void draw() {

    // clear the background
    background(0);
    
    // apply the simulation to the particles, and draw them to the screen
    ps.simulate();
    
    // add a new particle
    ps.addParticle();
}