Add API for adding areas to HUD

api.lua

@@ -1,7 +1,23 @@
+local hudHandlers = {}
+
+--- Adds a function as a HUD handler, it will be able to add items to the Areas HUD element.
+function areas:registerHudHandler(handler)
+	table.insert(hudHandlers, handler)
+end
+
+
+function areas:getExternalHudEntries(pos)
+	local areas = {}
+	for _, func in pairs(hudHandlers) do
+		func(pos, areas)
+	end
+	return areas
+end
 
 --- Returns a list of areas that include the provided position.
 function areas:getAreasAtPos(pos)
 	local res = {}
+
 	if self.store then
 		local a = self.store:get_areas_for_pos(pos, false, true)
 		for store_id, store_area in pairs(a) do

api.md

@@ -0,0 +1,45 @@
+Areas mod API
+===
+
+API list
+---
+
+ * `areas.registerHudHandler(handler)` - Registers a handler to add items to the Areas HUD.  See [HUD](#hud).
+
+
+HUD
+---
+
+If you are making a protection mod or a similar mod that adds invisible regions
+to the world, and you would like then to show up in the areas HUD element, you
+can register a callback to show your areas.
+
+HUD handler specification:
+
+ * `handler(pos, list)`
+   * `pos` - The position to check.
+   * `list` - The list of area HUD elements, this should be modified in-place.
+
+The area list item is a table containing a list of tables with the following fields:
+
+ * `id` - An identifier for the area. This should be a unique string in the format `mod:id`.
+ * `name` - The name of the area.
+ * `owner` - The player name of the region owner, if any.
+
+All of the fields are optional but at least one of them must be set.
+
+### Example
+
+	local function areas_hud_handler(pos, areas)
+		local val = find_my_protection(pos)
+
+		if val then
+			table.insert(areas, {
+				id = "mod:"..val.id,
+				name = val.name,
+				owner = val.owner,
+			})
+		end
+	end
+
+	areas:registerHudHandler(areas_hud_handler)

hud.lua

@@ -7,11 +7,21 @@ minetest.register_globalstep(function(dtime)
 		local name = player:get_player_name()
 		local pos = vector.round(player:getpos())
 		local areaStrings = {}
+
 		for id, area in pairs(areas:getAreasAtPos(pos)) do
 			table.insert(areaStrings, ("%s [%u] (%s%s)")
 					:format(area.name, id, area.owner,
 					area.open and ":open" or ""))
 		end
+
+		for i, area in pairs(areas:getExternalHudEntries(pos)) do
+			local str = ""
+			if area.name then str = area.name .. " " end
+			if area.id then str = str.."["..area.id.."] " end
+			if area.owner then str = str.."("..area.owner..")" end
+			table.insert(areaStrings, str)
+		end
+
 		local areaString = "Areas:"
 		if #areaStrings > 0 then
 			areaString = areaString.."\n"..