When using SwitchWithTransition for participating scenes Load and Unload are called twice

[karolmajta]

It can be easily reproduced by creating two scenes, the first one just transitions to second one. I'm not posting the snippet (for brevity), but it's easy enough to reproduce. There are logs which look like:

2023/12/13 17:55:53 Load Main Scene
2023/12/13 17:55:53 SwitchWithTransition called...
2023/12/13 17:55:53 Unload Main Scene <----------------- why would we unload the scene here? it still needs to be drawing
2023/12/13 17:55:53 Load Jump Scene <------------------ this is ok
2023/12/13 17:55:53 Draw in Main
2023/12/13 17:55:53 Draw in Jump
2023/12/13 17:55:53 Draw in Main
2023/12/13 17:55:53 Draw in Jump
...
2023/12/13 17:55:54 Draw in Jump
2023/12/13 17:55:54 Draw in Main
2023/12/13 17:55:54 Draw in Jump
2023/12/13 17:55:54 Unload Main Scene <---------------- this is expected here, scene is gone after transition so unload it
2023/12/13 17:55:54 Load Jump Scene <---------------- this scene's `Load` gets called second time
2023/12/13 17:55:54 Draw in Jump
2023/12/13 17:55:54 Draw in Jump
2023/12/13 17:55:54 Draw in Jump
...
^Csignal: interrupt

Question is - is this on purpose? If yes, I could live with that, but it seems a bit puzzling tbh.

[karolmajta]

I have a fix for this behavior, but I'd like to know if this is intentional. If yes, I'll just let it be.

[joelschutz]

This is really a bug that I left as a feature. At first I couldn't figure out how to solve it(since the new scene needs to be loaded with the previous state anyway), but found useful to have this double call to know where the transition start and end.

But you can make a suggestion and we can figure a way that is more explicit and compatible. The main thing that bothers me in this system is that the scene has no way to know if it's a transition or not. My first idea was to have a pre-transition(on old scene to extract the state) and post-transiton(on new scene to confirm complete load). But I didn't figured how it should work on a simple transition.

I'm on vacation now and can start to investigate a bit, feel free to help in the discussion or in a PR.