Leafdecay: Node timer based implementation, API

This implements a node-timer based leafdecay mechanism, and exposes
an API to use it in mods.

The API is documented in game_api.txt.

`default.register_leafdecay(leafdecaydef)`

`leafdecaydef` is a table, with following members:
{
	trunks = { "default:tree"}, -- nodes considered trunks
	leaves = { "default:leaves", "default:apple"}, -- nodes considered leaves
	radius = 3, -- activates leafdecay this far from the trunk
}

The algorithm will drop `leaves` items in the area if no `trunks` are found
in the `trunk_radius` sized area around the position of the leaf. If a node
listed in `leaves` has a group `leafdecay_drop > 0`, then the item is dropped,
otherwise the item is removed but not dropped.

The algorithm also implements a value `default.leafdecay_speed` (default
15) which can be modified to increase or decrease of the leaf decay. The
algorithm will vary the actual speed a bit to introduce randomness.

Leaf decay is randomized by 0.1 seconds to reduce the chance that
decay happens many times on the same second interval. This requires
nodetimer_interval to be set to values lower than 1.0 to have an
effect.

The leaves will decay between 2 and 10 seconds after digging the trunk,
and happen at non-integer second intervals.

-- The API was added by sofar.

game_api.txt

@@ -658,20 +658,36 @@ default.player_get_animation(player)
 Leafdecay
 ---------
 
-To enable leaf decay for a node, add it to the `leafdecay` group.
+To enable leaf decay for leaves when a tree is cut down by a player,
+register the tree with the default.register_leafdecay(leafdecaydef)
+function.
 
-The rating of the group determines how far from a node in the group `tree`
-the node can be without decaying.
+If `param2` of any registered node is ~= 0, the node will always be
+preserved. Thus, if the player places a node of that kind, you will
+want to set `param2 = 1` or so.
 
-If `param2` of the node is ~= 0, the node will always be preserved. Thus, if
-the player places a node of that kind, you will want to set `param2 = 1` or so.
+The function `default.after_place_leaves` can be set as
+`after_place_node of a node` to set param2 to 1 if the player places
+the node (should not be used for nodes that use param2 otherwise
+(e.g. facedir)).
 
-The function `default.after_place_leaves` can be set as `after_place_node of a node`
-to set param2 to 1 if the player places the node (should not be used for nodes
-that use param2 otherwise (e.g. facedir)).
+If the node is in the `leafdecay_drop` group then it will always be
+dropped as an item.
+
+`default.register_leafdecay(leafdecaydef)`
+
+`leafdecaydef` is a table, with following members:
+	{
+		trunks = {"default:tree"}, -- nodes considered trunks
+		leaves = {"default:leaves", "default:apple"},
+			-- nodes considered for removal
+		radius = 3, -- radius to consider for searching
+	}
+
+Note: all the listed nodes in `trunks` have their `on_after_destruct`
+callback overridden. All the nodes listed in `leaves` have their
+`on_timer` callback overridden.
 
-If the node is in the `leafdecay_drop` group then it will always be dropped as an
-item.
 
 Dyes
 ----

mods/default/functions.lua

@@ -325,47 +325,64 @@ default.after_place_leaves = function(pos, placer, itemstack, pointed_thing)
 	end
 end
 
--- Leafdecay ABM
-
-minetest.register_abm({
-	label = "Leaf decay",
-	nodenames = {"group:leafdecay"},
-	neighbors = {"air"},
-	interval = 2,
-	chance = 10,
-	catch_up = false,
-
-	action = function(pos, node, _, _)
-		-- Check if leaf is placed
-		if node.param2 ~= 0 then
-			return
+-- Leafdecay
+local function leafdecay_after_destruct(pos, oldnode, def)
+	for _, v in pairs(minetest.find_nodes_in_area(vector.subtract(pos, def.radius),
+			vector.add(pos, def.radius), def.leaves)) do
+		local node = minetest.get_node(v)
+		if node.param2 == 0 then
+			minetest.get_node_timer(v):start(math.random(20, 120) / 10)
+		end
+	end
 end
 
-		local rad = minetest.registered_nodes[node.name].groups.leafdecay
-		-- Assume ignore is a trunk, to make this
-		-- work at the border of a loaded area
-		if minetest.find_node_near(pos, rad, {"ignore", "group:tree"}) then
-			return
+local function leafdecay_on_timer(pos, def)
+	if minetest.find_node_near(pos, def.radius, def.trunks) then
+		return false
 	end
-		-- Drop stuff
-		local itemstacks = minetest.get_node_drops(node.name)
-		for _, itemname in ipairs(itemstacks) do
-			if itemname ~= node.name or
-					minetest.get_item_group(node.name, "leafdecay_drop") ~= 0 then
-				local p_drop = {
+
+	local node = minetest.get_node(pos)
+	local drops = minetest.get_node_drops(node.name)
+	for _, item in ipairs(drops) do
+		local is_leaf
+		for _, v in pairs(def.leaves) do
+			if v == item then
+				is_leaf = true
+			end
+		end
+		if minetest.get_item_group(item, "leafdecay_drop") ~= 0 or
+				not is_leaf then
+			minetest.add_item({
 				x = pos.x - 0.5 + math.random(),
 				y = pos.y - 0.5 + math.random(),
 				z = pos.z - 0.5 + math.random(),
-				}
-				minetest.add_item(p_drop, itemname)
+			}, item)
 		end
 	end
-		-- Remove node
+
 	minetest.remove_node(pos)
 	minetest.check_for_falling(pos)
 end
-})
 
+function default.register_leafdecay(def)
+	assert(def.leaves)
+	assert(def.trunks)
+	assert(def.radius)
+	for _, v in pairs(def.trunks) do
+		minetest.override_item(v, {
+			after_destruct = function(pos, oldnode)
+				leafdecay_after_destruct(pos, oldnode, def)
+			end,
+		})
+	end
+	for _, v in pairs(def.leaves) do
+		minetest.override_item(v, {
+			on_timer = function(pos)
+				leafdecay_on_timer(pos, def)
+			end,
+		})
+	end
+end
 
 --
 -- Convert dirt to something that fits the environment

mods/default/nodes.lua

@@ -2072,3 +2072,57 @@ minetest.register_node("default:cloud", {
 	sounds = default.node_sound_defaults(),
 	groups = {not_in_creative_inventory = 1},
 })
+
+--
+-- register trees for leafdecay
+--
+
+if minetest.get_mapgen_setting("mg_name") == "v6" then
+	default.register_leafdecay({
+		trunks = {"default:tree"},
+		leaves = {"default:apple", "default:leaves"},
+		radius = 2,
+	})
+
+	default.register_leafdecay({
+		trunks = {"default:jungletree"},
+		leaves = {"default:jungleleaves"},
+		radius = 3,
+	})
+
+	default.register_leafdecay({
+		trunks = {"default:pine_tree"},
+		leaves = {"default:pine_needles"},
+		radius = 3,
+	})
+else
+	default.register_leafdecay({
+		trunks = {"default:tree"},
+		leaves = {"default:apple", "default:leaves"},
+		radius = 3,
+	})
+
+	default.register_leafdecay({
+		trunks = {"default:jungletree"},
+		leaves = {"default:jungleleaves"},
+		radius = 2,
+	})
+
+	default.register_leafdecay({
+		trunks = {"default:pine_tree"},
+		leaves = {"default:pine_needles"},
+		radius = 2,
+	})
+end
+
+default.register_leafdecay({
+	trunks = {"default:acacia_tree"},
+	leaves = {"default:acacia_leaves"},
+	radius = 2,
+})
+
+default.register_leafdecay({
+	trunks = {"default:aspen_tree"},
+	leaves = {"default:aspen_leaves"},
+	radius = 3,
+})