-- subterrain 0.1.0 by paramat
-- For Minetest 0.4.8 stable
-- Depends default
-- License: code WTFPL

-- Parameters

local YMAX = -113
local TCAVE = 0.6 -- Cave threshold.
		-- 1 = small rare caves, 0 = 1/2 ground volume, 0.5 = 1/3rd ground volume 

-- 3D noise for caves

local np_cave = {
	offset = 0,
	scale = 1,
	spread = {x=768, y=256, z=768}, -- squashed 3:1
	seed = 59033,
	octaves = 6,
	persist = 0.63
}

-- Stuff

subterrain = {}

-- On generated function

minetest.register_on_generated(function(minp, maxp, seed)
	if maxp.y > YMAX then
		return
	end

	local t1 = os.clock()
	local x1 = maxp.x
	local y1 = maxp.y
	local z1 = maxp.z
	local x0 = minp.x
	local y0 = minp.y
	local z0 = minp.z
	
	print ("[subterrain] chunk minp ("..x0.." "..y0.." "..z0..")")
	
	local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
	local area = VoxelArea:new{MinEdge=emin, MaxEdge=emax}
	local data = vm:get_data()
	
	local c_air = minetest.get_content_id("air")
	
	local sidelen = x1 - x0 + 1
	local chulens = {x=sidelen, y=sidelen, z=sidelen}
	local minposxyz = {x=x0, y=y0, z=z0}
	
	local nvals_cave = minetest.get_perlin_map(np_cave, chulens):get3dMap_flat(minposxyz)
	
	local nixyz = 1
	for z = z0, z1 do -- for each xy plane progressing northwards
		for y = y0, y1 do -- for each x row progressing upwards
			local vi = area:index(x0, y, z)
			for x = x0, x1 do -- for each node do
				if nvals_cave[nixyz] > 0.6 then
					data[vi] = c_air
				end
				nixyz = nixyz + 1
				vi = vi + 1
			end
		end
	end
	
	vm:set_data(data)
	vm:set_lighting({day=0, night=0})
	vm:calc_lighting()
	vm:write_to_map(data)
	local chugent = math.ceil((os.clock() - t1) * 1000)
	print ("[subterrain] "..chugent.." ms")
end)