Dimensions, made easy.
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What it does, in more detail:
Any class that derives from the Subworld class is automatically registered as a subworld. Subworlds are highly customisable; from their size and how they generate, to whether they or the players inside of them save, to even what ModWorld is allowed to update while inside of them.
Loading a subworld is as simple as calling "SLWorld.EnterSubworld". Each subworld can have a custom loading UI if its class overrides "loadingUIState". The UI can even persist after the world is loaded if "loadingUI" is overridden.
Subworlds can be set to be either temporary or permanent. Subworlds can also prevent players from saving while inside them. Subworld Library also handles deleting subworlds when their main world is deleted.
Subworld Library doesn't just handle loading, saving, etc. in Singleplayer; it also does so in Multiplayer, with little to no extra work required on your end.
Subworld Library gets rid of Space, the Underworld, and both Oceans inside subworlds, freeing up tons of world space, and allowing for very small subworlds.
If you need help with making a subworld, or encounter a bug, please go to the #sublib_help and #sublib_bugs channels in the GaMeterraria Discord respectively.