Are you finding some objects are placed where you wouldn't want them? If so, which ones?
What I would like to get is an object that will block a path with specific height on it, just like the thing that is made of a stalagmite and a stalactite in irl caves, forgot it's name tho.
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Red is the object, transparent purple is the terrain.
Hmmm, it wouldn't be difficult to allow, there is a lot of effort made to stop that from happening at the moment! I guess the main issue is, is that something people generally want? Its not done by the in game generator, and so there are no object designed for it.
Also, just in case you haven't saw it, for some weird reason I installed MapGEN, I do not see any themes loaded. Any solutions that I can use?
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I would make sure that you are definitely running the latest version with it's own data, any stuff from old instals can do stuff like that. Check your data/generic/themes folder, it should have 31 named folders in it.
I would delete everything in your mapgen folder and run the installer again.