Add a use for dry sponges

Dry sponges act as air tanks while diving, but the effect is
limited by their tendency to soak up water from the environment.

mods/nc_player_hud/breath.lua

@@ -17,6 +17,7 @@ local breath_mask = "^[mask:nc_player_hud_breath_mask.png\\^[resize\\:" .. w ..
 
 nodecore.register_playerstep({
 		label = "breath hud",
+		priority = -1000,
 		action = function(player)
 			local br = player:get_breath()
 			nodecore.player_discover(player, "breath_" .. br)

mods/nc_sponge/diving.lua

@@ -0,0 +1,31 @@
+-- LUALOCALS < ---------------------------------------------------------
+local minetest, nodecore
+    = minetest, nodecore
+-- LUALOCALS > ---------------------------------------------------------
+
+local modname = minetest.get_current_modname()
+
+nodecore.register_playerstep({
+		label = "sponge diving breath",
+		action = function(player, data)
+			local breath = player:get_breath()
+
+			if breath > 0 then
+				local old = data.spongebreath or data.properties.breath_max
+				data.spongebreath = breath
+				if breath >= old then return end
+			end
+
+			local inv = player:get_inventory()
+			for i = 1, inv:get_size("main") do
+				if inv:get_stack("main", i):get_name() == modname .. ":sponge" then
+					local nb = breath + 2
+					if nb > data.properties.breath_max then
+						nb = data.properties.breath_max
+					end
+					data.spongebreath = nb
+					return player:set_breath(nb)
+				end
+			end
+		end
+	})

mods/nc_sponge/init.lua

@@ -10,4 +10,5 @@ include("abm")
 include("gen")
 include("cultivate")
 include("squeeze")
+include("diving")
 include("hints")