add-InteractorManagesTheEventLoop-flag.md

New flag vtkRenderWindowInteractor::InteractorManagesTheEventLoop for event loop

This flag is useful when you are integrating VTK in a larger system. In such cases, an application can lock up if the Start() method in vtkRenderWindowInteractor processes events indefinitely without giving the system a chance to execute anything. The default value for this flag is true. It currently only affects VTK webassembly applications.

As an example with webassembly in the browser through emscripten SDK:

1. If your app has an int main entry point, leave this value enabled. Emscripten will simulate an infinite event loop and avoid running code after interactor->Start() which is usually the end of main. Otherwise, all VTK objects will go out of scope immediately without giving a chance for user interaction with the render window.
2. If your app does not have an int main entry point, disable this behavior. Otherwise, the webassembly application will not start up successfully.