Gizmo giz[] = new Gizmo[700];
PImage typo;

void setup () {
  size (320, 240);
  stroke (0);
  background (255);
  typo = loadImage ("background.jpg");
  for (int i=0; i < giz.length; i++) {
    float x = random (width);
    float y = random (height);
    giz[i] = new Gizmo (x, y);
  }
}

void draw () {
  noStroke ();
  fill (255, 30);
  rect (0, 0, width, height);
  stroke (0);
  for (int i=0; i < giz.length; i++) {
    giz[i].move ();
    int x = int (giz[i].position.x);
    int y = int (giz[i].position.y);
    color pixel = typo.get (x, y);
    
    if (brightness (pixel) < 40) {
      point (x, y);
    }
  }
}

class Gizmo {
  
  PVector position;
  PVector direction;
  
  float spin = 0.15;
  
  Gizmo (float theX, float theY) {
    position    = new PVector (theX, theY);
    direction   = new PVector ();
    direction.x = random (-1, 1);
    direction.y = random (-1, 1);
  }
  
  void move () {
    direction.x += random (-spin, spin);
    direction.y += random (-spin, spin);
    direction.normalize ();
    position.add (direction);
    
    if (position.x < 0 || position.x > width) {
      direction.x *= -1;
    }
    if (position.y < 0 || position.y > height) {
      direction.y *= -1;
    }
  }
}