// A Vector is a magic array
// It's a bit like a pez dispenser, allowing you to add and subtract.
// Doing this with normal arrays is far more complicated and slower,
// so it's best to dive in and learn this very useful thing.
Vector draggables;

void setup(){
  size(400, 400);
  smooth();
  draggables = new Vector();
}

void draw(){
  background(100);
  for(int i = 0; i < draggables.size(); i++){
    // The Vector only knows we have Objects in there, not what they are
    // So we have to "cast" them (like a mould), ie: (datatype)variable
    Drag d = (Drag)draggables.get(i);
    d.draw();
  }
}

// This adds to the Vector of draggable objects.
// But only when you are not over an existing object
// otherwise you add to the list when dragging.
void mousePressed(){
  boolean mouseOver = false;
  for(int i = 0; i < draggables.size(); i++){
    Drag d = (Drag)draggables.get(i);
    if(d.over()){
	mouseOver = true;
    }
  }
  if(!mouseOver){
    draggables.add(new Drag(mouseX, mouseY, 50));
  }
}

class Drag{
  float x,y,big;
  boolean locked;
  Drag(float x, float y, float big){
    this.x = x;
    this.y = y;
    this.big = big;
  }
  void draw(){
    ellipse(x, y, big, big);
    
    // The dragging stuff goes in here.
    // use if(mousePressed) to turn locked on
    // and the else of that to turn it off.
    
  }
  boolean over(){
    if(dist(mouseX, mouseY, x, y) < big * 0.5){
	return true;
    }
    return false;
  }
}