By splitting a complex ray-casting process into different tasks performed on different processors, Voreen provides a lot of flexibility because users can intervene at different points during ray casting. Voreen's object-oriented design lets users easily create customized processor classes that cooperate seamlessly with existing classes. A user-friendly GUI supports rapid prototyping of visualization ideas. We've implemented several applications based on our library. In the future, we'd like to further extend Voreen's capabilities to make visualization prototyping even easier on all abstraction levels. Thus, we plan to realize a set of dedicated processor skeletons, which are solely configured through shader programs and can thus be modified at runtime.