// a list of all rectangles
Rectangle[] rectangles;
int rectanglesSize;

void setup(){
  size(500,600);
  smooth();

  rectanglesSize = 0;
  rectangles = new Rectangle[1];
}

void draw(){
  background(0);
  
  for( int i=0; i<rectanglesSize; i++ ){
    rectangles[i].draw();
  }
  
}

void addRectangle(Rectangle r){
  rectanglesSize++;
  if( rectangles.length == rectanglesSize ){
    rectangles = (Rectangle[]) expand(rectangles);
  }
  rectangles[rectanglesSize-1] = r;
}

void mousePressed(){
  
  Rectangle r = new Rectangle(mouseX, mouseY);
  addRectangle(r);
  
}

void mouseReleased(){
  
  rectangles[ rectanglesSize-1 ].finishDrawing( mouseX, mouseY );
  
}