is the Lua API available a closed thing
Yes, the APIs themselves are closed. Which is good, because if they changed too much then a lot of tools would constantly break.
Even though the API has not seen many changes from 3.0 to 3.1, the transition from 2.7 > 2.8 > 3.0 required changes to many tools.
For example, you have repeatedly used your “personalized scrollbar” (I do not know what to call it.). It is a clear sign that it is necessary.
You can call it vScrollbar 
But IMHO, you’re just pointing out what is potentially nice about using something like vLib:
- You don’t have to wait for Renoise to implement feature XYZ (assuming of course that the feature can be implemented with scripting).
- When/if the feature arrives, the vLib framework can replace it’s custom implementation with the native one.
- Usually without any need to change the source code of the tool itself, as vLib is closely modelled after the viewbuilder API
That’s usually the point with frameworks - that they abstract away the implementation details.
As for your checkbox suggestion, vLib features the “vToggleButton” which largely works like you suggest
You can see it working by cloning the vLib demo from github
I’m the one managing Renoise API suggestions, btw. Do you know of the API wishlist?
https://forum.renoise.com/t/the-api-wishlist-thread/29285