mapgen.lua

local has_bedrock_mod = minetest.get_modpath("bedrock")
local has_vacuum_mod = minetest.get_modpath("vacuum")

-- http://dev.minetest.net/PerlinNoiseMap
-- https://github.com/pyrollo/cratermg/blob/master/init.lua (thx Pyrollo:)


-- basic planet height noise
local height_params = {
	offset = 0,
	scale = 5,
	spread = {x=256, y=256, z=256},
	seed = 5477835,
	octaves = 2,
	persist = 0.5
}

-- mountain noise
local mountain_params = {
	offset = 0,
	scale = 5,
	spread = {x=256, y=256, z=256},
	seed = 34252,
	octaves = 3,
	persist = 0.5
}

-- clay noise
local cave_params = {
	offset = 0,
	scale = 1,
	spread = {x=128, y=64, z=128},
	seed = 981364,
	octaves = 2,
	persist = 0.5
}

-- cave biomes
local biome_params = {
	offset = 0,
	scale = 5,
	spread = {x=256, y=256, z=256},
	seed = 5477835,
	octaves = 2,
	persist = 0.5
}


local c_base = minetest.get_content_id("default:desert_stone")
local c_stone = minetest.get_content_id("default:desert_stone")
local c_sand = minetest.get_content_id("default:desert_sand")

local c_dirt_with_grass = minetest.get_content_id("default:dirt_with_grass")
local c_dirt_with_rainforest_litter = minetest.get_content_id("default:dirt_with_rainforest_litter")
local c_dirt_with_dry_grass = minetest.get_content_id("default:dirt_with_dry_grass")
local c_dirt_with_coniferous_litter = minetest.get_content_id("default:dirt_with_coniferous_litter")
local c_dirt_with_snow = minetest.get_content_id("default:dirt_with_snow")
local c_permafrost = minetest.get_content_id("default:permafrost")

local c_air = minetest.get_content_id("air")
local c_airlight = minetest.get_content_id("planet_mars:airlight")
local c_vacuum = c_air

if has_vacuum_mod then
	c_vacuum = minetest.get_content_id("vacuum:vacuum")
end

local c_bedrock = c_base

if has_bedrock_mod then
	c_bedrock = minetest.get_content_id("bedrock:bedrock")
end

local y_start = planet_mars.y_start
local y_height = planet_mars.y_height

-- perlin noise
local height_perlin
local mountain_perlin
local cave_perlin
local biome_perlin

-- reuse maps
local height_perlin_map = {}
local mountain_perlin_map = {}
local cave_perlin_map = {}
local biome_perlin_map = {}

minetest.register_on_generated(function(minp, maxp)

	if minp.y < y_start or minp.y > (y_start + y_height) then
		-- not in range
		return
	end

	local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
	local area = VoxelArea:new{MinEdge=emin, MaxEdge=emax}
	local data = vm:get_data()

	local side_length = maxp.x - minp.x + 1 -- 80
	local map_lengths_xyz = {x=side_length, y=side_length, z=side_length}

	height_perlin = height_perlin or minetest.get_perlin_map(height_params, map_lengths_xyz)
	mountain_perlin = mountain_perlin or minetest.get_perlin_map(mountain_params, map_lengths_xyz)
	biome_perlin = biome_perlin or minetest.get_perlin_map(biome_params, map_lengths_xyz)
	cave_perlin = cave_perlin or minetest.get_perlin_map(cave_params, map_lengths_xyz)

	height_perlin:get_2d_map_flat({x=minp.x, y=minp.z}, height_perlin_map)
	mountain_perlin:get_2d_map_flat({x=minp.x, y=minp.z}, mountain_perlin_map)
	biome_perlin:get_2d_map_flat({x=minp.x, y=minp.z}, biome_perlin_map)
	cave_perlin:get_3d_map_flat(minp, cave_perlin_map)

	-- TODO: surface/cave y-check for perfomance

	local perlin_index = 1

	for z=minp.z,maxp.z do
	for x=minp.x,maxp.x do

		-- normalized factor from 0...1
		local height_perlin_factor = math.min(1, math.abs( height_perlin_map[perlin_index] * 0.1 ) )
		local mountain_perlin_factor = math.min(1, math.abs( mountain_perlin_map[perlin_index] * 0.18 ) )

		-- weighted hill top and solid bottom
		local abs_height = y_start + (y_height * 0.99) + (y_height * height_perlin_factor * 0.01)
		local abs_mountain_height = y_start + (y_height * 0.9) + (y_height * mountain_perlin_factor * 0.1)

		for y=minp.y,maxp.y do
			local index = area:index(x,y,z)

			if y <  y_start + 10 then
				-- bedrock (if available)
				data[index] = c_bedrock

			elseif y < abs_height then
				-- solid
				data[index] = c_base

			elseif y < abs_mountain_height then
				-- mountain
				data[index] = c_stone

			elseif y < abs_height + 2 then
				-- top layer
				data[index] = c_sand

			else
				-- non-solid
				data[index] = c_vacuum
			end

		end --y

		perlin_index = perlin_index + 1
	end --x
	end --z

	local perlin_index_2d = 1
	local perlin_index_3d = 1

	-- generate caves
	for z=minp.z,maxp.z do
	for y=minp.y,maxp.y do
	for x=minp.x,maxp.x do
		local index = area:index(x,y,z)

		local is_cave = math.abs(cave_perlin_map[perlin_index_3d]) > 0.5
		local is_cave_dirt = math.abs(cave_perlin_map[perlin_index_3d]) < 0.55

		local is_deep = y < (y_start + (y_height * 0.95))

		if data[index] == c_base then
			-- base material found

			if is_cave and is_deep then
				-- caves only deep below
				if is_cave_dirt then

					-- normalized factor from 0...1
					local biome_perlin_factor = math.min(1, math.abs( biome_perlin_map[perlin_index_2d] * 0.1 ) )

					if biome_perlin_factor > 0.9 then
						data[index] = c_base
					elseif biome_perlin_factor > 0.7 then
						data[index] = c_dirt_with_dry_grass
					elseif biome_perlin_factor > 0.5 then
						data[index] = c_dirt_with_coniferous_litter
					elseif biome_perlin_factor > 0.4 then
						data[index] = c_dirt_with_rainforest_litter
					elseif biome_perlin_factor > 0.3 then
						data[index] = c_permafrost
					elseif biome_perlin_factor > 0.1 then
						data[index] = c_dirt_with_grass
					else
						data[index] = c_dirt_with_snow
					end

				else
					-- cave with air
					if math.random(0, 5) == 1 then
						-- light source
						data[index] = c_airlight
					else
						data[index] = c_air
					end
				end

			end
		end

		perlin_index_3d = perlin_index_3d + 1
		perlin_index_2d = perlin_index_2d + 1
	end --x

	perlin_index_2d = z - minp.z + 1

	end --y
	end --z

	vm:set_data(data)

	if maxp.y < y_start + (y_height * 0.95) then
		-- create decos and ores below certain depth
		minetest.generate_decorations(vm, minp, maxp)
		minetest.generate_ores(vm, minp, maxp)
	end

	vm:set_lighting({day=15, night=0})
	vm:write_to_map()

end)