* Overlay actors are drawn in a separate pass, after all non-overlay actors within the Layer.
* For overlay actors, the drawing order is determined by the hierachy (depth-first search order),
* and depth-testing will not be used.
* Overlay actors are drawn in a separate pass, after all non-overlay actors within the Layer.
* For overlay actors, the drawing order is determined by the hierachy (depth-first search order),
* and depth-testing will not be used.