int numBalls = 25;			 //total number of balls
float spring = .1;		     //how springy something is?
float gravity = 1;			 //gravity
float friction = -0.1;		   //friction between balls?
Ball[] balls = new Ball[numBalls];   //an array of Ball called balls set to the number of balls in length?

void setup() 
{
  size(1000, 700);
  noStroke();
  smooth();
  for (int i = 0; i < numBalls; i++) {  //cycle thru the array of balls
    balls[i] = new Ball(random(width), random(height), random(50, 250), i, balls); //construct each one.. what are the last two parameters?
  }
}

void draw() 
{
  background(50);
  for (int i = 0; i < numBalls; i++) {
    balls[i].collide();
    balls[i].move();
    balls[i].display();    //call balls functions
  }
}

class Ball {
  float x, y;	 //variables for x,y
  float diameter;   //variable for diameter
  float vx = 0;     //velocity in x direction?
  float vy = 0;     //velocity in y direction?
  int id;	     //which ball?
  Ball[] others;    //another array of Ball called others
 
  Ball(float xin, float yin, float din, int idin, Ball[] oin) {  //arguments for Ball
    x = xin;
    y = yin;
    diameter = din;
    id = idin;
    others = oin;
  } 
  
  void collide() {
    for (int i = id + 1; i < numBalls; i++) { //scroll thru every ball in the array setting its position up one?
	float dx = others[i].x - x;		 //distance to the other ball in x direction?
	float dy = others[i].y - y;		 //distance to the other ball in y direction?
	float distance = sqrt(dx*dx + dy*dy);
	float minDist = others[i].diameter/2 + diameter/2;  //min distance = distance between other ball radius plus radius?
	if (distance < minDist) {				   //if the distance is less than the minimum distance?
	  float angle = atan2(dy, dx);			    //calculate angle of?
	  float targetX = x + cos(angle) * minDist;
	  float targetY = y + sin(angle) * minDist;
	  float ax = (targetX - others[i].x) * spring;	 //i dont have clue
	  float ay = (targetY - others[i].y) * spring;
	  vx -= ax;
	  vy -= ay;
	  others[i].vx += ax;
	  others[i].vy += ay;					   //still no clue
	}
    }   
  }
  
  void move() {						    //no clue
    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() {					  //draw ball
    fill(0,200,50, 204);
    stroke(0);
    strokeWeight(5);
    ellipse(x, y, diameter, diameter);
  }
}