Show HUD element only if looking at rotatable node

hud.lua

@@ -4,6 +4,11 @@ local ipairs
 local minetest, vector
     = minetest, vector
 
+local rotate = include("rotate")
+
+local TEX_ROTATE_CLOCKWISE         = "nc_extended_rotating_hud_rotate_clockwise.png"
+local TEX_ROTATE_COUNTER_CLOCKWISE = "nc_extended_rotating_hud_rotate_counter_clockwise.png"
+
 local player_huds = {}
 
 local function do_player_rotating_checks(player)
@@ -11,6 +16,7 @@ local function do_player_rotating_checks(player)
 
     local hud_index = player_huds[name]
     if hud_index then
+        -- FIXME: Only remove / update HUD elements when necessary.
         player:hud_remove(hud_index)
         player_huds[name] = nil
     end
@@ -27,13 +33,20 @@ local function do_player_rotating_checks(player)
 
     local node = nil
     local ray = minetest.raycast(eye_pos, eye_pos + look_dir * reach, false, false)
-    for pointed_thing in ray do node = pointed_thing end
+    for pointed_thing in ray do
+        if pointed_thing.type == "node" then
+            node = minetest.get_node(pointed_thing.under)
+            break
+        end
+    end
 
-    if node then
+    if node and rotate.is_rotatable(node) then
+        local is_sneaking = player:get_player_control().sneak
+        local texture = is_sneaking and TEX_ROTATE_COUNTER_CLOCKWISE or TEX_ROTATE_CLOCKWISE
         hud_index = player:hud_add({
             hud_elem_type = "image",
             name = "rotation hint",
-            text = "nc_extended_rotating_hud_rotate_clockwise.png",
+            text = texture,
             position  = { x = 0.5, y = 0.5 },
             offset    = { x = 0, y = 0 },
             alignment = { x = 0, y = 0 },

rotate.lua

@@ -39,13 +39,19 @@ for up_index, up in ipairs(AXIS_LOOKUP) do
     end
 end
 
+-- Returns whether the specified `node` is rotatable by this mod.
+-- TODO: Register such that only certain nodes may be rotated.
+local function is_rotatable(node)
+    local def = minetest.registered_nodes[node.name]
+    return def.paramtype2 == "facedir"
+end
+rotate.is_rotatable = is_rotatable
+
 -- Rotates `node` at the specified `pos` around `axis` by `degrees` counter-clockwise.
 local function rotate_node(pos, node, axis, degrees)
     if degrees % 90 ~= 0 then error("degrees must be divisible by 90") end
     if axis_vector_to_index(axis) == nil then error("axis must be an axis vector") end
-
+    if not is_rotatable(node) then error("node is not rotatable") end
-    local def = minetest.registered_nodes[node.name]
-    if def.paramtype2 ~= "facedir" then error("node's paramtype2 is not 'facedir'") end
 
     local up   = AXIS_LOOKUP[1 + math.floor(node.param2 / 4)]
     local back = minetest.facedir_to_dir(node.param2)