add ambience sounds and helper function (#87)

* add ambience sounds and helper function

* minor tweaks

* fix deps

---------

Co-authored-by: BuckarooBanzay <BuckarooBanzay@users.noreply.github.com>

ambience.lua

@@ -0,0 +1,73 @@
+
+-- currently playing sounds per mapblock
+-- mapblock_pos[number]
+local currently_playing = {}
+
+-- clear the currently playing tracker every few seconds
+local function clear_currently_playing()
+    currently_playing = {}
+    minetest.after(5, clear_currently_playing)
+end
+minetest.after(5, clear_currently_playing)
+
+-- mapblock resolution
+local function get_key(pos)
+    return minetest.pos_to_string(vector.round(vector.divide(pos, 16)))
+end
+
+local function add_currently_playing(pos, value)
+    local key = get_key(pos)
+    local count = currently_playing[key]
+    if not count then
+        -- new entry
+        count = value
+    else
+        -- update entry
+        count = count + value
+    end
+    currently_playing[key] = count
+end
+
+-- limit plaing sounds per mapblock
+local function can_play(pos)
+    local count = currently_playing[get_key(pos)]
+    return not count or count < 25
+end
+
+-- register ambience sounds with node-timer
+function scifi_nodes.register_ambience(nodename, soundname, opts)
+    assert(opts)
+    opts.interval = opts.interval or 60
+
+    local function play(pos)
+        minetest.sound_play(soundname ,{
+            max_hear_distance = opts.max_hear_distance or 16,
+            pos = pos,
+            gain = opts.gain or 0.7
+        })
+    end
+
+    minetest.override_item(nodename, {
+        on_timer = function(pos)
+            local timer = minetest.get_node_timer(pos)
+
+            if not can_play(pos) then
+                -- too many sounds playing, recheck again soon
+                timer:start(1)
+                return
+            end
+
+            -- increment usage count
+            add_currently_playing(pos, 1)
+            play(pos)
+
+            -- restart timer
+            timer:start(opts.interval)
+        end,
+        on_construct = function(pos)
+            play(pos)
+            local timer = minetest.get_node_timer(pos)
+            timer:start(opts.interval)
+        end
+    })
+end