solution and testcase for issue #1421 (ScreenshotAppState never cleans up)

[stephengold]

No description provided.

[MeFisto94]

I couldn't connect how a SceneProcessor could cleanup the AbstractAppState initally, but apparently there is a name clash between SceneProcessor#cleanup and AbstractAppState#cleanup, where from AAS we call SP#cleanup, which in turn invokes on our AppState.

Your workaround will work, super.cleanup is no problem for the current code (because it only sets a boolean), but there might be a more clever way.
I am sure @pspeed42 has had this case a few times already and knows something clever?

What I could imagine is that making the Processor an internal class (could even be anonymous, I guess) would make this code more clean and avoid such a hack, then.
Essentially those are two classes anyway, the appstate only does the lifecycle management of the Processor.

[pspeed42]

Since I was tagged: Yeah, my own personal idiomatic approach is to avoid excessive multiclassing just for (fake) convenience. So that app state has to be an app state because that's what it is. It should not also be a scene processor... because it's an app state. The issue described is one of a half-dozen pitfalls to the 'quick and dirty' approach uses in this app state... but probably too long to go into here.

[stephengold]

If there's no further discussion, I'd like to integrate this PR today.