add forcefields, size is 31k, can be configured.

mods/mapgen/forcefields.lua

@@ -0,0 +1,53 @@
+--forcefields, used to limit the world size. Once the walls have been assembled you can disable the mod by commenting out line 13 for mapgen/init.lua
+
+-- configure world size here - max = 30000, min = 32 (can be smaller, spawn might be outside of area.)
+
+-- note: default settings are 31000
+
+-- Warning: you will have to set all six dimensions.
+
+x_pos_position = 31000
+x_nega_position = -31000
+
+y_pos_position = 31000
+y_nega_position = -31000
+
+z_pos_position = 31000
+z_nega_position = -31000
+
+minetest.register_node("mapgen:force_field", {
+	description = "Alien Forcefield",
+	tiles = {"mapgen_force.png"},
+	sunlight_propagates = true,
+	paramtype = "light",
+	drawtype = "glasslike",
+	inventory_image = minetest.inventorycube("mapgen_force_inv_wield.png"),
+	wield_image = minetest.inventorycube("mapgen_force_inv_wield.png"),
+	is_ground_content = true,
+	groups = {not_in_creative_inventory=1},
+})
+
+-- sorry, inefficient code - can't do any better yet. not unless a contributor wants to improve it.
+
+minetest.register_abm({
+	nodenames = {"air"},
+	interval = 2,
+	chance = 1,
+	action = function(pos, node)
+		if x_nega_position == pos.x then
+			minetest.set_node(pos, {name="mapgen:force_field"})
+		elseif x_pos_position == pos.x then
+			minetest.set_node(pos, {name="mapgen:force_field"})
+		elseif y_nega_position == pos.y then
+			minetest.set_node(pos, {name="mapgen:force_field"})
+		elseif y_pos_position == pos.y then
+			minetest.set_node(pos, {name="mapgen:force_field"})
+		elseif z_nega_position == pos.z then
+			minetest.set_node(pos, {name="mapgen:force_field"})
+		elseif z_pos_position == pos.z then
+			minetest.set_node(pos, {name="mapgen:force_field"})
+		else
+			--no forcefields constructed.
+		end
+	end,
+})

mods/mapgen/init.lua

@@ -9,6 +9,9 @@ dofile(minetest.get_modpath("mapgen").."/nodes.lua")
 dofile(minetest.get_modpath("mapgen").."/flowers.lua")
 dofile(minetest.get_modpath("mapgen").."/functions.lua")
 
+-- enable forcefields (useful for server admins
+dofile(minetest.get_modpath("mapgen").."/forcefields.lua")
+
 minetest.register_alias("mapgen_stair_cobble", "stairs:stair_cobble")
 minetest.register_alias("mapgen_water_source", "mapgen:water_source")
 minetest.register_alias("mapgen_lava_source", "mapgen:lava_source")
@@ -861,17 +864,3 @@ minetest.register_node(":base:leaves", {
 	groups = {crumbly=3, soil=1, not_in_creative_inventory=1},
 	sounds = default.node_sound_dirt_defaults(),
 })
-
-minetest.register_node("mapgen:force_field", {
-	description = "Alien Forcefield",
-	tiles = {
-		{name="mapgen_force.png", animation={type="vertical_frames", aspect_w=128, aspect_h=128, length=1.5}},
-	},
-	sunlight_propagates = true,
-	paramtype = "light",
-	drawtype = "glasslike",
-	inventory_image = minetest.inventorycube("mapgen_force_inv_wield.png"),
-	wield_image = minetest.inventorycube("mapgen_force_inv_wield.png"),
-	is_ground_content = true,
-	groups = {not_in_creative_inventory=1},
-})