make leaves fall down when unsupported.

also refactor leaves registration code.

mods/bg_tree/node.lua

@@ -35,32 +35,53 @@ reg_log("sapling", {
 	drop = modname .. ":log",
 })
 
-local function reg_leaves (name, desc, drop, texture, groups)
-	groups = groups or {}
-	groups.planty = 1
-	groups.air_flowable = 1
 
-	texture = texture or name
 
-	drop = drop or name
-
-	blockgame.register_node(modname .. ":" .. name, {
-		description = desc,
-		drawtype = "glasslike",
-		tiles = {
-			modname .. "_" .. texture .. ".png",
-		},
-		paramtype = "light",
-		sunlight_propagates = true,
-		groups = groups,
-		drop = modname .. ":" .. drop,
-	})
+local function leaves_fall_check (pos, node)
+	return blockgame.every(blockgame.vector.get_neighbors(pos), function (pos)
+		return minetest.get_item_group(minetest.get_node(pos).name, "supports_leaves") == 0
+	end)
 end
 
-reg_leaves("leaves", "Leaves")
-reg_leaves("leaves_growing", "Growing Leaves", "leaves", "leaves_alive")
-reg_leaves("leaves_alive", "Leaves", "leaves")
-reg_leaves("leaves_decomposing", "Decomposing Leaves")
+local function reg_leaves (name, def)
+	def.description = def.description or name
+	def.texture = def.texture or name
+	def.tiles = {modname .. "_" .. def.texture .. ".png"}
+
+	def.drawtype = "glasslike"
+	def.paramtype = "light"
+	def.sunlight_propagates = true
+
+	def.groups = blockgame.underride(def.groups, {
+		planty = 1,
+		supports_leaves = 1,
+		air_flowable = 1,
+		can_fall = 1,
+	})
+
+	blockgame.register_node(modname .. ":" .. name, def)
+end
+
+reg_leaves("leaves", {
+	description = "Leaves",
+})
+reg_leaves("leaves_growing", {
+	description = "Growing Leaves",
+	drop = modname .. ":leaves",
+	texture = "leaves_alive",
+	fall_check = leaves_fall_check,
+})
+reg_leaves("leaves_alive", {
+	description = "Leaves",
+	drop = modname .. ":leaves",
+	fall_check = leaves_fall_check,
+})
+reg_leaves("leaves_decomposing", {
+	description = "Decomposing Leaves",
+	groups = {
+		supports_leaves = 0,
+	},
+})
 
 blockgame.reg_simple_node("nut", "Nut", {
 	woody = 1,