Previously, only nodes strictly within the map block were being carved out as open space. This meant that multi-node decorations (such as giant mushrooms) would collide with walls and ceilings that would be carved out by adjacent block generation later, leaving them sliced off.
Now Subterrane carves out border regions too. Make note of the is_ground_content function, put all your decoration nodes into this to prevent them from being removed. Can't rely on just is_ground_function node properties for most situations, it's too simplistic.
This is actually just a representation of Perlin noise that's been
edited to look like the minimap, but it conveys the basic intent of this
mod reasonably well IMO.
