Currently we have a lot of calls to RenderingManager::GetInstance() to receive the rendering manager singleton and work with it. This is typically done to perform some actions on all render windows (which are handled by the global rendering manager singleton).
However, it is possible to register render windows with an individual rendering manager, leading to something like
The second option is not a good option in my opinion since it explicitly requires a specific, magic string. The first option only works if you already have a render window at hand.
I think we never faced the problem of needing multiple rendering managers. Also, this was done to only use the rendering manager singleton: rMITK5e0e87c36865: Handle RenderingManager like the singleton it is.
Reason for this topic to come up was the latest PR on GitHub: https://github.com/MITK/MITK/pull/248
On the user list the user struggled with the difference between the two functions accessing the "global" or "local" rendering manager.