create mapper prototype.

create a node that scans the area around it and creates a smaller
replica of it out of entities.

mods/bg_map/entity.lua

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+local modname = minetest.get_current_modname()
+
+local function yoink_texture (tiles)
+	local result = {}
+	for _, tile in pairs(tiles) do
+		table.insert(result, tile)
+	end
+	while #result < 6 do
+		table.insert(result, result[#result])
+	end
+	return result
+end
+
+local function cube_texture (texture)
+	return { texture, texture, texture, texture, texture, texture, }
+end
+
+minetest.register_entity(modname .. ":projection", {
+	initial_properties = {
+		pointable = false,
+		visual = "cube",
+		textures = cube_texture(modname .. "_mapper.png"),
+		visual_size = {
+			x = 1/4,
+			y = 1/4,
+			z = 1/4,
+		},
+	},
+	on_activate = function (self, static_data, deltatime)
+		local data = minetest.parse_json(static_data)
+		if not data then return end
+
+		self._projected_node = data.projected_node
+		local node_def = minetest.registered_items[self._projected_node]
+		self._texture = yoink_texture(node_def.tiles)
+
+		self.object:set_properties({
+			textures = self._texture,
+		})
+	end,
+	get_staticdata = function (self)
+		return minetest.write_json({
+			texture = self._texture,
+			projected_node = self._projected_node,
+		})
+	end,
+	on_step = function (self, deltatime, moveresult)
+		if math.random() > 0.99 ^ deltatime then
+			self.object:remove()
+		end
+	end,
+})

mods/bg_map/init.lua

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+load_file("node")
+load_file("entity")
+load_file("map")

mods/bg_map/map.lua

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+local modname = minetest.get_current_modname()
+
+local function spawn_projection (pos, nodename)
+	return minetest.add_entity(pos, modname .. ":projection", minetest.write_json({
+		projected_node = nodename,
+	}))
+end
+
+local function step_to_delta (step, size)
+	return vector.new(
+		step % size,
+		math.floor(step / (size ^ 2)) % size,
+		math.floor(step / size) % size
+	)
+end
+
+local function project_at (pos, step, config)
+	config = config or {}
+	config.scan_distance = config.scan_distance or 8
+	config.projection_scale = config.projection_scale or 1/4
+
+	local sd = config.scan_distance
+	local pos_delta = step_to_delta(step, sd*2 + 1) - vector.new(sd, sd, sd)
+
+	local target = pos + pos_delta
+	local projected_pos = pos + pos_delta * config.projection_scale
+
+	if minetest.get_node(projected_pos).name ~= "air" then return end
+
+	local nodename = minetest.get_node(target).name
+	if nodename == "air" then return end
+
+	spawn_projection(projected_pos, nodename)
+end
+
+blockgame.register_abm({
+	label = "project maps",
+	nodenames = {modname .. ":mapper"},
+	interval = 1,
+	chance = 1,
+	action = function (pos, node)
+		local meta = minetest.get_meta(pos)
+		local step = meta:get_int("step")
+
+		local count = math.random(16, 32)
+		for i=1, count do
+			project_at(pos, step)
+			step = step + 1
+		end
+
+		step = step % ((8*2 + 1) ^ 3) -- TODO: don't have this hardcoded.
+
+		meta:set_int("step", step)
+	end,
+})

mods/bg_map/mod.conf

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+name = bg_map
+description = in-world mapping of the game world for blockgame.
+depends = bg_api

mods/bg_map/node.lua

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+local modname = minetest.get_current_modname()
+
+blockgame.register_node(modname .. ":mapper", {
+	description = "Mapper",
+	groups = {
+		cracky = 3,
+	},
+	on_construct = function (pos)
+		local meta = minetest.get_meta(pos)
+		meta:set_int("step", 0)
+	end,
+})