Leaf decay, based on the groups 'leafdecay' and 'tree'

mods/default/init.lua

@@ -11,8 +11,9 @@ LIGHT_MAX = 14
 -- Definitions made by this mod that other mods can use too
 default = {}
 
--- Register and define map generator stuff
+-- Load other files
 dofile(minetest.get_modpath("default").."/mapgen.lua")
+dofile(minetest.get_modpath("default").."/leafdecay.lua")
 
 --
 -- Tool definition
@@ -808,7 +809,7 @@ minetest.register_node("default:tree", {
 	description = "Tree",
 	tile_images = {"default_tree_top.png", "default_tree_top.png", "default_tree.png"},
 	is_ground_content = true,
-	groups = {snappy=2,choppy=2,oddly_breakable_by_hand=1},
+	groups = {tree=1,snappy=2,choppy=2,oddly_breakable_by_hand=1},
 	sounds = default.node_sound_wood_defaults(),
 })
 
@@ -816,7 +817,7 @@ minetest.register_node("default:jungletree", {
 	description = "Jungle Tree",
 	tile_images = {"default_jungletree_top.png", "default_jungletree_top.png", "default_jungletree.png"},
 	is_ground_content = true,
-	groups = {snappy=2,choppy=2,oddly_breakable_by_hand=1},
+	groups = {tree=1,snappy=2,choppy=2,oddly_breakable_by_hand=1},
 	sounds = default.node_sound_wood_defaults(),
 })
 
@@ -839,7 +840,7 @@ minetest.register_node("default:leaves", {
 	visual_scale = 1.3,
 	tile_images = {"default_leaves.png"},
 	paramtype = "light",
-	groups = {snappy=3},
+	groups = {snappy=3, leafdecay=3},
 	drop = {
 		max_items = 1,
 		items = {

mods/default/leafdecay.lua

@@ -0,0 +1,76 @@
+-- minetest/default/leafdecay.lua
+
+-- To enable leaf decay for a node, add it to the "leafdecay" group.
+--
+-- The rating of the group determines how far from a node in the group "tree"
+-- the node can be without decaying.
+--
+-- 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.
+
+default.leafdecay_trunk_cache = {}
+default.leafdecay_enable_cache = true
+
+minetest.register_abm({
+	nodenames = {"group:leafdecay"},
+	neighbors = {"air", "group:liquid"},
+	-- A low interval and a high inverse chance spreads the load
+	interval = 2,
+	chance = 5,
+
+	action = function(p0, node, _, _)
+		--print("leafdecay ABM at "..p0.x..", "..p0.y..", "..p0.z..")")
+		local do_preserve = false
+		local d = minetest.registered_nodes[node.name].groups.leafdecay
+		if not d or d == 0 then
+			--print("not groups.leafdecay")
+			return
+		end
+		local n0 = minetest.env:get_node(p0)
+		if n0.param2 ~= 0 then
+			--print("param2 ~= 0")
+			return
+		end
+		local p0_hash = nil
+		if default.leafdecay_enable_cache then
+			p0_hash = minetest.hash_node_position(p0)
+			local trunkp = default.leafdecay_trunk_cache[p0_hash]
+			if trunkp then
+				local n = minetest.env:get_node(trunkp)
+				local reg = minetest.registered_nodes[n.name]
+				if reg.groups.tree and reg.groups.tree ~= 0 then
+					--print("cached trunk still exists")
+					return
+				end
+				--print("cached trunk is invalid")
+				-- Cache is invalid
+				table.remove(default.leafdecay_trunk_cache, p0_hash)
+			end
+		end
+		for dx = -d, d do if do_preserve then break end
+		for dy = -d, d do if do_preserve then break end
+		for dz = -d, d do if do_preserve then break end
+			local p = {
+				x = p0.x + dx,
+				y = p0.y + dy,
+				z = p0.z + dz,
+			}
+			local n = minetest.env:get_node(p)
+			local reg = minetest.registered_nodes[n.name]
+			if reg.groups.tree and reg.groups.tree ~= 0 then
+				do_preserve = true
+				if default.leafdecay_enable_cache then
+					--print("caching trunk")
+					-- Cache the trunk
+					default.leafdecay_trunk_cache[p0_hash] = p
+				end
+			end
+		end
+		end
+		end
+		if not do_preserve then
+			minetest.env:remove_node(p0)
+		end
+	end
+})
+