This example is for Processing 3+. If you have a previous version, use the examples included with your software. If you see any errors or have suggestions, please let us know.

Smoke Particle System by Daniel Shiffman. * A basic smoke effect using a particle system. Each particle is rendered as an alpha masked image.

```
ParticleSystem ps;

void setup() {
size(640, 360);
ps = new ParticleSystem(0, new PVector(width/2, height-60), img);
}

void draw() {
background(0);

// Calculate a "wind" force based on mouse horizontal position
float dx = map(mouseX, 0, width, -0.2, 0.2);
PVector wind = new PVector(dx, 0);
ps.applyForce(wind);
ps.run();
for (int i = 0; i < 2; i++) {
}

// Draw an arrow representing the wind force
drawVector(wind, new PVector(width/2, 50, 0), 500);
}

// Renders a vector object 'v' as an arrow and a position 'loc'
void drawVector(PVector v, PVector loc, float scayl) {
pushMatrix();
float arrowsize = 4;
// Translate to position to render vector
translate(loc.x, loc.y);
stroke(255);
// Call vector heading function to get direction (note that pointing up is a heading of 0) and rotate
// Calculate length of vector & scale it to be bigger or smaller if necessary
float len = v.mag()*scayl;
// Draw three lines to make an arrow (draw pointing up since we've rotate to the proper direction)
line(0, 0, len, 0);
line(len, 0, len-arrowsize, +arrowsize/2);
line(len, 0, len-arrowsize, -arrowsize/2);
popMatrix();
}

// A class to describe a group of Particles
// An ArrayList is used to manage the list of Particles

class ParticleSystem {

ArrayList<Particle> particles;    // An arraylist for all the particles
PVector origin;                   // An origin point for where particles are birthed
PImage img;

ParticleSystem(int num, PVector v, PImage img_) {
particles = new ArrayList<Particle>();              // Initialize the arraylist
origin = v.copy();                                   // Store the origin point
img = img_;
for (int i = 0; i < num; i++) {
particles.add(new Particle(origin, img));         // Add "num" amount of particles to the arraylist
}
}

void run() {
for (int i = particles.size()-1; i >= 0; i--) {
Particle p = particles.get(i);
p.run();
particles.remove(i);
}
}
}

// Method to add a force vector to all particles currently in the system
void applyForce(PVector dir) {
// Enhanced loop!!!
for (Particle p : particles) {
p.applyForce(dir);
}
}

}
}

// 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.copy();
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) {
}

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

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

// Is the particle still useful?