example of ixee UI element renderer code

gistfile1.java

public interface UIGenericElementRenderer<T extends glEEngine> {
  public void unsafeDraw(UIElement elem, T engine);
}

public abstract class UIElementRenderer<T extends glEEngine, U extends UIElement> implements UIGenericElementRenderer<T> {
  Class<U> myClass;

  public UIElementRenderer(Class<U> rendereeClass) {
    myClass = rendereeClass;
  }

  public Class<U> drawFor() { return myClass; }

  public abstract void draw(U elem, ElementDrawer<T> drawer);

  public void unsafeDraw(UIElement elem, ElementDrawer<T> drawer) {
    draw((U)elem, engine);
  }
}

public interface ElementDrawer<T> {
  public void draw(UIElement e);

  public T backend();
}

public class OGLElementDrawer implements ElementDrawer<glEEngine> {
  glEEngine backend;

  static Map<Class, UIElementRenderer> renderers = new HashMap<Class, UIElementRenderer>();

  static {
    register(new UITextRenderer());
  }

  private static void register(UIElementRenderer renderer) {
    renderers.put(renderer.drawFor(), renderer);
  }

  public OGLElementDrawer(glEEngine e) {
    backend = e;
  }

  public glEEngine backend() {
    return backend;
  }

  /*
   * unchecked warning is generated by call to unsafeDraw
   * unsafeDraw is actually unsafe (typecasts arg to type expected for renderer)
   * but because UIElementRenderer is parameterized on the type it draws for,
   * and returns that class via drawFor(),
   * the register method here guarantees that if an entry exists for an elem's class
   * then the renderer associated will draw its class
   *
   * this guarantees the typecast in unsafeDraw is actually safe,
   * so it is okay to suppress this warning.
  */
  @SuppressWarnings("unchecked")
  public void draw(UIElement e) {
    UIElementRenderer renderer = renderers.get(e.getClass());
    if (renderer == null) {
      throw new RuntimeException("No renderer available for " + e); //TODO: NoRendererException
    }
    renderer.unsafeDraw(e, this);
  }
}

public class UITextRenderer extends UIElementRenderer<glEEngine, UIText> {
  public UITextRenderer() {
    super(UIText.class);
  }

  public void draw(UIText elem, ElementDrawer<glEEngine> drawer) {
    // rendering logic
  }
}