Example ScreenGraph

ScreenGraphExample.pde

Game game;
Element e;
void setup() {
  size(640, 480, P3D);
  noStroke();
  e = new MouseMoved();
  
  //e.transformation.scale(10);
  //e.transformation.rotate(PI / 4);
  e.addChild(new Circle(30, 10)).transformation.scale(10);;

  game = new Game(this);
  game.layers.add(e);
  //subElement.transformation.scale(.5);
}

void draw() {
  background(66);
  text(frameRate, 20, 20);
  e.transformation.rotate(PI * .01);
  game.run();
  ellipse(0, 0, 30, 30);
}
class Circle extends Element {
  Circle(float x, float y) {
    super(x, y);
  }
  @Override
    public void displayImpl(PGraphics pg) {
    ellipse(0, 0, 1, 1);
  }
}
class MouseMoved extends Element {
 @Override
 public void update() {
   position.x = mouseX;
   position.y = mouseY;
   super.update();
 }
}
class Game {
  PApplet parent;
  PGraphics offscreen;
  ArrayList<Element> layers = new ArrayList<Element>();
  Game(PApplet _parent) {
    parent = _parent;
    offscreen = parent.g;
  }
  void run() {
    if (offscreen != parent.g)
      offscreen.beginDraw();

    for (Element layer : layers)
      layer.update();

    for (Element layer : layers)
      layer.display(offscreen);

    if (offscreen != parent.g)
      offscreen.endDraw();
  }
}

class Element {
  PVector position;
  ArrayList<Element> children;
  PMatrix transformation;

  int getChildrenCount() {
    if (children == null)
      return 0;

    return children.size();
  }
  Element addChild(Element child) {
    if (children == null)
      children = new ArrayList<Element>();

    children.add(child);
    return child;
  }
  boolean removeChild(Element child) {
    if (children == null || !children.contains(child))
      return false;

    children.remove(child);
    return true;
  }
  Element() {
    this(new PVector());
  }
  Element(float x, float y, float z) {
    this(new PVector(x, y, z));
  }

  Element(float x, float y) {
    this(new PVector(x, y));
  }
  Element(PVector _position) {
    position = _position;
    if (g.is3D())
      transformation = new PMatrix3D();
    if (g.is2D())
      transformation = new PMatrix2D();
  }

  void update() {
    if (getChildrenCount() > 0)
      for (Element child : children)
        child.update();
  }

  void display(PGraphics pg) {
    //pg.beginDraw();
    pg.pushMatrix();
    pg.translate(position.x, position.y);
    pg.applyMatrix(transformation);
    displayImpl(pg);
    if (getChildrenCount() > 0)
      for (Element child : children) {
        child.display(pg);
      }
    pg.popMatrix();
    //pg.endDraw();
  }
  void displayImpl(PGraphics pg) {

    if (pg.is3D()) {
      box(10);
    } else if (pg.is2D()) {
      rect(0, 0, 10, 10);
    }
  }
}