Distance and easing decay

sketch_160801a.pde

ArrayList<Ball> balls;

boolean doScale;

void setup() {
  doScale = false;
  size(1280, 720);
  balls = new ArrayList<Ball>();
  for (int i=0; i<width/20; i++) {
    for (int j=0; j<height/20; j++) {
      Ball b = new Ball();
      b.setup(i*20, j*20);
      balls.add(b);
    }
  }

  fill(255);
  noStroke();
}

void draw() {
  background(0);
  for (int i=0; i<balls.size(); i++) {
    balls.get(i).update(mouseX, mouseY);
  }


  for (int i=0; i<balls.size(); i++) {
    balls.get(i).draw();
  }
}


void mousePressed() {
  doScale = !doScale;
}




class Ball {

  float scale, 
        dScale;
  
  float x,
        y;
        
  float decay;

  void setup(float _x, float _y) {
    x = _x;
    y = _y;
    scale = 5.0f;
    decay = 64.0f; // change this to make the ease faster (4.0 is pretty quick but nice)
  }

  void update(int _mx, int _my) {
    if (doScale) {
      
      float aDist = dist(_mx, _my, x, y);
      if(aDist < 3.0f) aDist = 3.0f; // prevent division by zero 
      dScale = 1500.0f/aDist;
      
    } else {
      dScale = 3.0f;
    }
    scale += (dScale - scale)/decay; // this is the meat of the ease!
  }
  
  void draw() {
    ellipse(x, y, scale, scale);
  }

}