Systems, methods, and computer readable media for implementing reentrant compositing window manager applications are described. In general, techniques are disclosed for using a second application to composite portions of hierarchically structured objects and the window manager to composite certain other portions of the same object. More particularly, a window manager application may be used to composite objects of a first type (e.g., application backing store bitmaps) and then call or invoke a second application to composite objects of a second type (e.g., hierarchically structured objects). The second type of object includes information (e.g., a reference) of the composite window manager's output buffer at the time the second application was invoked. This knowledge may be used by the second application to call back into the window manager in a manner that permits the generation of unique visual effects without violating modern memory management scriptures regarding the separation of application memory spaces.