// A Bubble class
  class Bubble {
    float x,y;
    float diameter;
    float speed;
    float r,g;
    
    Bubble(float r_,float g_, float diameter_) {
      x = random(width);
      y = height;
      r = r_;
      g = g_;
      diameter = diameter_;
    }
    
    // True or False if point is inside circle
    boolean rollover(int mx, int my) {
      if (dist(mx,my,x,y) < diameter/2) {
        return true;
      } else {
        return false;
      }
    }
    
    // Change Bubble variables
    void change() {
      r = constrain(r + random(-10,10),0,255);
      g = constrain(g + random(-10,10),0,255);
      diameter = constrain(diameter + random(-2,4),4,72);
    }
    
    // Display Bubble
    void display() {
      stroke(0);
      fill(r,g,255,150);
      ellipse(x,y,diameter,diameter);
    }
    
    // Bubble drifts upwards
    void drift() {
      y += random(-3,-0.1);
      x += random(-1,1);
      if (y < -diameter*2) {
        y = height + diameter*2;
      }
    }
  }