One last refactor to ambient sounds.

Make tree sounds managed by the mod that defines the nodes in
question using register_ambient, consistent with other things like
fluids.

nc_envsounds is now responsible for just the air moving and
cave dripping sounds made by air itself.

Common windiness logic moved into api layer.

mods/nc_api/util_sound.lua

@@ -3,8 +3,8 @@ local ItemStack, ipairs, math, minetest, nodecore, pairs, type, unpack,
       vector
     = ItemStack, ipairs, math, minetest, nodecore, pairs, type, unpack,
       vector
-local math_exp, math_random
-    = math.exp, math.random
+local math_exp, math_random, math_sin, math_sqrt
+    = math.exp, math.random, math.sin, math.sqrt
 -- LUALOCALS > ---------------------------------------------------------
 
 local oldplay = minetest.sound_play
@@ -15,6 +15,12 @@ function minetest.sound_play(name, spec, ...)
 	return oldplay(name, spec, ...)
 end
 
+function nodecore.windiness(y)
+	if y < 0 then return 0 end
+	if y > 512 then y = 512 end
+	return math_sqrt(y) * (1 + 0.5 * math_sin(minetest.get_gametime() / 5))
+end
+
 function nodecore.stack_sounds(pos, kind, stack)
 	stack = stack or nodecore.stack_get(pos)
 	stack = ItemStack(stack)

mods/nc_envsound/init.lua

@@ -1,32 +1,10 @@
 -- LUALOCALS < ---------------------------------------------------------
 local math, minetest, nodecore, pairs, vector
     = math, minetest, nodecore, pairs, vector
-local math_exp, math_random, math_sin, math_sqrt
-    = math.exp, math.random, math.sin, math.sqrt
+local math_exp, math_random
+    = math.exp, math.random
 -- LUALOCALS > ---------------------------------------------------------
 
-local function windiness(y)
-	if y < 0 then return 0 end
-	if y > 512 then y = 512 end
-	return math_sqrt(y) * (1 + 0.5 * math_sin(minetest.get_gametime() / 5))
-end
-
-nodecore.register_ambiance({
-		label = "Tree Leaves Ambiance",
-		nodenames = {"nc_tree:leaves"},
-		neigbors = {"air"},
-		interval = 1,
-		chance = 100,
-		sound_name = "nc_envsound_tree",
-		check = function(pos)
-			pos.y = pos.y + 1
-			if pos.y <= 0 then return end
-			return minetest.get_node(pos).name == "air"
-			and minetest.get_node_light(pos, 0.5) == 15
-			and { gain = windiness(pos.y) / 20 }
-		end
-	})
-
 local function check(pos, done)
 	local sp = {
 		x = pos.x + math_random() * 64 - 32,
@@ -46,7 +24,7 @@ local function check(pos, done)
 		if sp.y <= 0 then return end
 		minetest.sound_play("nc_envsound_air", {
 				pos = sp,
-				gain = windiness(sp.y) / 100
+				gain = nodecore.windiness(sp.y) / 100
 			})
 	elseif light < 4 then
 		minetest.sound_play("nc_envsound_drip", {

mods/nc_tree/ambiance.lua

@@ -0,0 +1,20 @@
+-- LUALOCALS < ---------------------------------------------------------
+local minetest, nodecore
+    = minetest, nodecore
+-- LUALOCALS > ---------------------------------------------------------
+
+nodecore.register_ambiance({
+		label = "Tree Leaves Ambiance",
+		nodenames = {"nc_tree:leaves"},
+		neigbors = {"air"},
+		interval = 1,
+		chance = 100,
+		sound_name = "nc_tree_breeze",
+		check = function(pos)
+			pos.y = pos.y + 1
+			if pos.y <= 0 then return end
+			return minetest.get_node(pos).name == "air"
+			and minetest.get_node_light(pos, 0.5) == 15
+			and { gain = nodecore.windiness(pos.y) / 20 }
+		end
+	})

mods/nc_tree/init.lua

@@ -12,3 +12,5 @@ include("stick")
 include("schematic")
 include("decor")
 include("cultivation")
+
+include("ambiance")