by Daniel Shiffman. A basic smoke effect using a particle system. Each particle is rendered as an alpha masked image.
Original Processing.org Example: SmokeParticleSystem
// All Examples Written by Casey Reas and Ben Fry // unless otherwise stated. ParticleSystem ps; Random generator; void setup() { size(200, 200); frameRate(30); colorMode(RGB, 255, 255, 255, 100); generator = new Random(); // Create an alpha masked image to be applied as the particle's texture PImage msk = loadImage("texture.gif"); PImage img = new PImage(msk.width,msk.height); for (int i = 0; i < img.pixels.length; i++) img.pixels[i] = color(255); img.mask(msk); ps = new ParticleSystem(0,new Vector3D(width/2,height-20),img); smooth(); } void draw() { background(0); // Calculate a "wind" force based on mouse horizontal position float dx = (mouseX - width/2) / 1000.0; Vector3D wind = new Vector3D(dx,0,0); ps.add_force(wind); ps.run(); for (int i = 0; i < 2; i++) { ps.addParticle(); } // Draw an arrow representing the wind force drawVector(wind, new Vector3D(width/2,50,0),500); } // Renders a vector object 'v' as an arrow and a location 'loc' void drawVector(Vector3D v, Vector3D loc, float scayl) { pushMatrix(); float arrowsize = 4; // Translate to location 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 rotate(v.heading2D()); // Calculate length of vector & scale it to be bigger or smaller if necessary float len = v.magnitude()*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 simple Particle class, renders the particle as an image class Particle { Vector3D loc; Vector3D vel; Vector3D acc; float timer; PImage img; // One constructor Particle(Vector3D a, Vector3D v, Vector3D l, PImage img_) { acc = a.copy(); vel = v.copy(); loc = l.copy(); timer = 100.0; img = img_; } // Another constructor (the one we are using here) Particle(Vector3D l,PImage img_) { acc = new Vector3D(0.0,0.0,0.0); float x = (float) generator.nextGaussian()*0.3f; float y = (float) generator.nextGaussian()*0.3f - 1.0f; vel = new Vector3D(x,y,0); loc = l.copy(); timer = 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 add_force(Vector3D f) { acc.add(f); } // Method to update location void update() { vel.add(acc); loc.add(vel); timer -= 2.5; acc.setXY(0,0); } // Method to display void render() { imageMode(CORNER); tint(255,timer); image(img,loc.x-img.width/2,loc.y-img.height/2); } // Is the particle still useful? boolean dead() { if (timer <= 0.0) { return true; } else { return false; } } } // A class to describe a group of Particles // An ArrayList is used to manage the list of Particles class ParticleSystem { ArrayList particles; // An arraylist for all the particles Vector3D origin; // An origin point for where particles are birthed PImage img; ParticleSystem(int num, Vector3D v, PImage img_) { particles = new ArrayList(); // 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() { // Cycle through the ArrayList backwards b/c we are deleting for (int i = particles.size()-1; i >= 0; i--) { Particle p = (Particle) particles.get(i); p.run(); if (p.dead()) { particles.remove(i); } } } // Method to add a force vector to all particles currently in the system void add_force(Vector3D dir) { for (int i = particles.size()-1; i >= 0; i--) { Particle p = (Particle) particles.get(i); p.add_force(dir); } } void addParticle() { particles.add(new Particle(origin,img)); } void addParticle(Particle p) { particles.add(p); } // A method to test if the particle system still has particles boolean dead() { if (particles.isEmpty()) { return true; } else { return false; } } } public class Vector3D { public float x; public float y; public float z; Vector3D(float x_, float y_, float z_) { x = x_; y = y_; z = z_; } Vector3D(float x_, float y_) { x = x_; y = y_; z = 0f; } Vector3D() { x = 0f; y = 0f; z = 0f; } void setX(float x_) { x = x_; } void setY(float y_) { y = y_; } void setZ(float z_) { z = z_; } void setXY(float x_, float y_) { x = x_; y = y_; } void setXYZ(float x_, float y_, float z_) { x = x_; y = y_; z = z_; } void setXYZ(Vector3D v) { x = v.x; y = v.y; z = v.z; } public float magnitude() { return (float) Math.sqrt(x*x + y*y + z*z); } public Vector3D copy() { return new Vector3D(x,y,z); } public Vector3D copy(Vector3D v) { return new Vector3D(v.x, v.y,v.z); } public void add(Vector3D v) { x += v.x; y += v.y; z += v.z; } public void sub(Vector3D v) { x -= v.x; y -= v.y; z -= v.z; } public void mult(float n) { x *= n; y *= n; z *= n; } public void div(float n) { x /= n; y /= n; z /= n; } /*public float dot(Vector3D v) { //implement DOT product }*/ /*public Vector3D cross(Vector3D v) { //implement CROSS product }*/ public void normalize() { float m = magnitude(); if (m > 0) { div(m); } } public void limit(float max) { if (magnitude() > max) { normalize(); mult(max); } } public float heading2D() { float angle = (float) Math.atan2(-y, x); return -1*angle; } public Vector3D add(Vector3D v1, Vector3D v2) { Vector3D v = new Vector3D(v1.x + v2.x,v1.y + v2.y, v1.z + v2.z); return v; } public Vector3D sub(Vector3D v1, Vector3D v2) { Vector3D v = new Vector3D(v1.x - v2.x,v1.y - v2.y,v1.z - v2.z); return v; } public Vector3D div(Vector3D v1, float n) { Vector3D v = new Vector3D(v1.x/n,v1.y/n,v1.z/n); return v; } public Vector3D mult(Vector3D v1, float n) { Vector3D v = new Vector3D(v1.x*n,v1.y*n,v1.z*n); return v; } public float distance (Vector3D v1, Vector3D v2) { float dx = v1.x - v2.x; float dy = v1.y - v2.y; float dz = v1.z - v2.z; return (float) Math.sqrt(dx*dx + dy*dy + dz*dz); } }