Add 'spawn' mod to spawn new players in suitable starting biomes (#2091)

Disabled in mgv6 and singlenode mapgens, by setting, or if
'static_spawnpoint' is set.

Cleanup format of minetest.conf.example.

mods/spawn/init.lua

@@ -0,0 +1,124 @@
+-- Disable by mapgen, setting or if 'static_spawnpoint' is set
+--------------------------------------------------------------
+
+local mg_name = minetest.get_mapgen_setting("mg_name")
+if mg_name == "v6" or mg_name == "singlenode" or
+		minetest.settings:get("static_spawnpoint") or
+		minetest.settings:get_bool("engine_spawn") then
+	return
+end
+
+
+-- Parameters
+-------------
+
+-- Resolution of search grid in nodes.
+local res = 64
+-- Number of points checked in the square search grid (edge * edge).
+local checks = 128 * 128
+-- Starting point for biome checks. This also sets the y co-ordinate for all
+-- points checked, so the suitable biomes must be active at this y.
+local pos = {x = 0, y = 8, z = 0}
+
+
+-- Table of suitable biomes
+
+local biome_ids = {
+	minetest.get_biome_id("taiga"),
+	minetest.get_biome_id("coniferous_forest"),
+	minetest.get_biome_id("deciduous_forest"),
+	minetest.get_biome_id("grassland"),
+	minetest.get_biome_id("savanna"),
+}
+
+-- End of parameters
+--------------------
+
+
+-- Direction table
+
+local dirs = {
+	{x = 0, y = 0, z = 1},
+	{x = -1, y = 0, z = 0},
+	{x = 0, y = 0, z = -1},
+	{x = 1, y = 0, z = 0},
+}
+
+
+-- Initial variables
+
+local edge_len = 1
+local edge_dist = 0
+local dir_step = 0
+local dir_ind = 1
+local searched = false
+local success = false
+local spawn_pos = {}
+
+
+--Functions
+-----------
+
+-- Get next position on square search spiral
+
+local function next_pos()
+	if edge_dist == edge_len then
+		edge_dist = 0
+		dir_ind = dir_ind + 1
+		if dir_ind == 5 then
+			dir_ind = 1
+		end
+		dir_step = dir_step + 1
+		edge_len = math.floor(dir_step / 2) + 1
+	end
+
+	local dir = dirs[dir_ind]
+	local move = vector.multiply(dir, res)
+
+	edge_dist = edge_dist + 1
+
+	return vector.add(pos, move)
+end
+
+
+-- Spawn position search
+
+local function search()
+	for iter = 1, checks do
+		local biome_data = minetest.get_biome_data(pos)
+		-- Sometimes biome_data is nil
+		local biome = biome_data and biome_data.biome
+		for id_ind = 1, #biome_ids do
+			local biome_id = biome_ids[id_ind]
+			if biome == biome_id then
+				local spawn_y = minetest.get_spawn_level(pos.x, pos.z)
+				if spawn_y then
+					spawn_pos = {x = pos.x, y = spawn_y, z = pos.z}
+					return true
+				end
+			end
+		end
+
+		pos = next_pos()
+	end
+
+	return false
+end
+
+
+-- On new player spawn
+
+-- Search for new player spawn once per server session. If successful, store
+-- position and reposition new players, otherwise leave them at engine spawn
+-- position.
+
+minetest.register_on_newplayer(function(player)
+	if not searched then
+		success = search()
+		searched = true
+	end
+
+	if success then
+		player:setpos(spawn_pos)
+	end
+end)