int nrBubbles = 40;
Bubble[] m_bubbles = new Bubble[nrBubbles];

private int m_oldX;
private int m_oldY;

void setup(){
  size(350, 350);
  colorMode(HSB, 100);
  smooth();
  frameRate(15);
    for (int i = 0; i < nrBubbles; i++){
      m_bubbles[i] = new Bubble();
    }
  }
  
  void draw(){
    background(color(0, 0, 255));
    for(int i = 0; i < nrBubbles; i++){
      m_bubbles[i].drawBubble();
     }
  }

  
 class Bubble{
   float m_x;
   float m_y;
   float m_r;
   color m_color;
   float m_maxSize;
   int m_iteration;
   
   public Bubble(){
      initialize();
   }
   
  public void drawBubble(){
      m_r += random(1, 5);
      m_iteration++;
      // desaturate color
      float h = hue(m_color);
      float s = saturation(m_color);
      float v = brightness(m_color);
      m_color = color(h, s - 5, v);
      fill(m_color);
      stroke(color(h, s, 80));
      strokeWeight(m_iteration);
      ellipse(m_x, m_y, m_r, m_r);
      if (m_r > m_maxSize){
        initialize();
      }
  }
  
  private void initialize(){
    m_r = random(1, 20);
    m_x = random(0, width);
    m_y = random(0, height);
    int xChange = 0;
    int yChange = 0;
    if (mouseX > 0 && mouseX < (width - 5) && mouseY > 0 && mouseY < (height - 5)) {
        // adapt position to mouse
        xChange = (int)((mouseX - m_x) * 0.4);
        yChange = (int)((mouseY - m_y) * 0.4);
    }
    m_x += xChange;
    m_y += yChange;
    m_color = color((int)random(0, 100), 100, 100);
    m_maxSize= random(width/8, width/5);
    m_iteration = 1;
    }
}