int numSpots = 50;
int selected = 0;
Spot[] spots = new Spot[numSpots];

void setup() {
  size(500,500);
  smooth();
  noStroke();
  for (int i=0; i < numSpots; i++) {
    spots[i] = new Spot(50+(50*i), 50, 10, i);
  }
}

void draw() {
  fill(0,15);
  rect(0,0,width,height);
  fill(255,30);
  for (int i=0; i < numSpots; i++) {
    spots[i].move();
    spots[i].display();
  }
}

void mousePressed () {
  spots[selected].start(mouseX, mouseY, mouseX%20, mouseY%20+1);
  selected++;
  if (selected >= numSpots) {
    selected = 0;
  }
}



class Spot {
  float x,y;
  float diameter;
  float speed;
  int direction = 1;

  Spot(float xpos, float ypos, float dia, float sp) {
    x = xpos;
    y = ypos;
    diameter = dia;
    speed = sp;
  }

  void start(float xpos, float ypos, float dia, float sp) {
    x = xpos;
    y = ypos;
    diameter = dia;
    speed = sp;
  }

  void move() {
    y += (speed * direction);

    if ((y > (height - diameter/2)) ||  (y < diameter/2)) {
      direction *= -1;
    }
  }

  void display () {
    ellipse(x, y, diameter, diameter);
  }
}