nc_extended_rotating/hud.lua

local ipairs
    = 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)
    local name = player:get_player_name()

    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

    local look_dir   = player:get_look_dir()
    local player_pos = vector.copy(player:get_pos())
    local eye_offset = vector.divide(player:get_eye_offset(), 10)
    local eye_height = player:get_properties().eye_height;
    local eye_pos    = player_pos + eye_offset + vector.new(0, eye_height, 0)

    local default_reach = minetest.registered_items[""].range or 4
    local wielded_reach = player:get_wielded_item():get_definition().reach
    local reach = wielded_reach or default_reach

    local node = nil
    local ray = minetest.raycast(eye_pos, eye_pos + look_dir * reach, false, false)
    for pointed_thing in ray do
        if pointed_thing.type == "node" then
            node = minetest.get_node(pointed_thing.under)
            break
        end
    end

    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 = texture,
            position  = { x = 0.5, y = 0.5 },
            offset    = { x = 0, y = 0 },
            alignment = { x = 0, y = 0 },
            scale     = { x = 1, y = 1 },
        })
        player_huds[name] = hud_index
    end
end

minetest.register_globalstep(function(delta_time)
    for _, player in ipairs(minetest.get_connected_players()) do
        do_player_rotating_checks(player)
    end
end)

minetest.register_on_leaveplayer(function(player)
    local name = player:get_player_name()
    player_huds[name] = nil
end)