make decomposing leaves have layers.

decomposing leaves now stack in layers, each one 1/4 of a node in
height.

currently this doesn't affect their behaviour, beyond making them stack
when placed or landing.

mods/bg_tree/decompose.lua

@@ -41,8 +41,8 @@ local average_leaves_per_dirt = 4
 blockgame.register_increasing_abm({
 	id = modname .. ":decompose",
 	label = "decompose leaves",
-	nodenames = {leaves_decomposing},
-	neighbors = {"group:dirty", leaves_decomposing},
+	nodenames = {"group:leaves_decomposing"},
+	neighbors = {"group:dirty", "group:leaves_decomposing"},
 	interval = 30,
 	chance = 10,
 	rate = function (pos, node, data)

mods/bg_tree/node_leaves.lua

@@ -1,13 +1,18 @@
 local modname = minetest.get_current_modname()
 
 local function reg_leaves (name, def)
-	def.description = def.description or name
-	def.texture = def.texture or name
-	def.tiles = {modname .. "_" .. def.texture .. ".png"}
+	local texture = def.texture or name
 
-	def.drawtype = "glasslike"
-	def.paramtype = "light"
-	def.sunlight_propagates = true
+	def = blockgame.underride(def, {
+		description = name,
+
+		texture = texture,
+		tiles = {modname .. "_" .. texture .. ".png"},
+
+		drawtype = "allfaces_optional",
+		paramtype = "light",
+		sunlight_propagates = true,
+	})
 
 	def.groups = blockgame.underride(def.groups, {
 		planty = 1,
@@ -55,9 +60,64 @@ reg_leaves("leaves_alive", {
 		falling_node = 0,
 	},
 })
-reg_leaves("leaves_decomposing", {
-	description = "Decomposing Leaves",
-	groups = {
-		supports_leaves = 0,
-	},
-})
+
+-- TODO: generalize stacking node registration and put into API.
+local decomposing_leaves_layers = 4
+
+local after_place_stack = function (pos)
+	local node = minetest.get_node(pos)
+	local below = pos + blockgame.vector.dirs.down
+	local below_node = minetest.get_node(below)
+	if not blockgame.starts_with(below_node.name, modname .. ":leaves_decomposing") then return end
+
+	local def = minetest.registered_nodes[node.name]
+	local below_def = minetest.registered_nodes[below_node.name]
+
+	if below_def.level == decomposing_leaves_layers then return end
+	local max_diff = decomposing_leaves_layers - below_def.level
+	local diff = math.min(max_diff, def.level)
+
+	minetest.swap_node(below, {name = modname .. ":leaves_decomposing_" .. (below_def.level + diff)})
+	if diff == def.level then
+		minetest.remove_node(pos)
+	else
+		minetest.swap_node(pos, {name = modname .. ":leaves_decomposing_" .. (def.level - diff)})
+	end
+end
+
+local function reg_decomposing (level)
+	local height = level / decomposing_leaves_layers
+
+	local description = "Decomposing Leaves (" .. level .. "/" .. decomposing_leaves_layers .. ")"
+	if level == decomposing_leaves_layers then description = "Decomposing Leaves" end
+
+	local drawtype = "nodebox"
+	local node_box = {
+		["type"] = "fixed",
+		fixed = { -0.5, -0.5, -0.5, 0.5, -0.5 + height, 0.5 },
+	}
+	if level == decomposing_leaves_layers then
+		drawtype = "allfaces_optional"
+		node_box = nil
+	end
+
+	reg_leaves("leaves_decomposing_" .. level, {
+		description = description,
+		level = level,
+		level_max = decomposing_leaves_layers,
+		texture = "leaves_decomposing",
+		drawtype = drawtype,
+		node_box = node_box,
+		after_place_node = after_place_stack,
+		after_land = after_place_stack,
+		drop = modname .. ":leaves_decomposing_1 " .. level,
+		groups = {
+			leaves_decomposing = level,
+		},
+	})
+end
+for level=1, decomposing_leaves_layers do
+	reg_decomposing(level)
+end
+
+minetest.register_alias(modname .. ":leaves_decomposing", modname .. ":leaves_decomposing_" .. decomposing_leaves_layers)