ParticleSystem ps;
  Random generator;
  
  void setup() {
  
    size(640, 200);
    colorMode(RGB, 255, 255, 255, 100);
  
    // Using a Java random number generator for Gaussian random numbers
    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 PVector(width/2,height-20 ),img);
  
    smooth();
  }
  
  void draw() {
    background(75);
  
    // Calculate a "wind" force based on mouse horizontal position
    float dx = (mouseX - width/2) / 1000.0;
    PVector wind = new PVector(dx,0,0);
    displayVector(wind,width/2,50,500);
    ps.add_force(wind);
    ps.run();
    for (int i = 0; i < 2; i++) {
      ps.addParticle();
    }
  }
  
   void displayVector(PVector v, float x, float y, float scayl) {
      pushMatrix();
      float arrowsize = 4;
      // Translate to location to render vector
      translate(x,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.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();
    }