Smiling Madness - OpenProcessing

mySketch
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// hit key "s" to make them all smile...
​
int numBalls = 12;
float spring = 0.05;
float gravity = 0.03;
float friction = -0.9;
Ball[] balls = new Ball[numBalls];
​
void setup() {
  size(640, 360);
  for (int i = 0; i < numBalls; i++) {
    balls[i] = new Ball(random(width), random(height), random(30, 70), i, balls);
  }
  noStroke();
  fill(255, 204);
}
​
void draw() {
  background(0);
  for (Ball ball : balls) {
    ball.collide();
    ball.move();
    ball.display();  
  }
}
​
class Ball {
  
  float x, y;
  float diameter;
  float vx = 0;
  float vy = 0;
  int id;
  Ball[] others;
 
  Ball(float xin, float yin, float din, int idin, Ball[] oin) {
    x = xin;
    y = yin;
    diameter = din;
    id = idin;
    others = oin;
  } 
  
  void collide() {
    for (int i = id + 1; i < numBalls; i++) {
      float dx = others[i].x - x;
      float dy = others[i].y - y;
      float distance = sqrt(dx*dx + dy*dy);
      float minDist = others[i].diameter/2 + diameter/2;
      if (distance < minDist) { 
        float angle = atan2(dy, dx);
        float targetX = x + cos(angle) * minDist;
        float targetY = y + sin(angle) * minDist;
        float ax = (targetX - others[i].x) * spring;
        float ay = (targetY - others[i].y) * spring;
        vx -= ax;
        vy -= ay;
        others[i].vx += ax;
        others[i].vy += ay;
      }
    }   
  }
  
  void move() {
    vy += gravity;
    x += vx;
    y += vy;
    if (x + diameter/2 > width) {
      x = width - diameter/2;
      vx *= friction; 
    }
    else if (x - diameter/2 < 0) {
      x = diameter/2;
      vx *= friction;
    }
    if (y + diameter/2 > height) {
      y = height - diameter/2;
      vy *= friction; 
    } 
    else if (y - diameter/2 < 0) {
      y = diameter/2;
      vy *= friction;
    }
  }
  
  void display() {
    fill(0, 0, 255);
    ellipse(x, y, diameter, diameter);
    fill(255);
    ellipse(x-10, y-5, 20, 20);
    ellipse(x+10, y-5, 20, 20);
    fill(0);
    ellipse(x-10, y-5, 10, 10);
    ellipse(x+10, y-5, 10, 10); 
    fill(255, 0, 0);
    arc(x, y+6, 40, 30, 0, 3.14);
  }
}
​
void keyPressed() {
  if (key == 's') {
    fill(0, 0, 255);
    ellipse(320, 230, 200, 150);
    fill(255);
    ellipse(300, 200, 50, 50);
    ellipse(350, 200, 50, 50);
    fill(0);
    ellipse(300, 200, 20, 20);
    ellipse(350, 200, 20, 20); 
    fill(255, 0, 0);
    arc(320, -230, 150, 150, 0, PI);
  }
}
​