blockgame/mods/bg_tree/grow_leaves.lua

local modname = minetest.get_current_modname()

-- NODE NAMES

local log_alive = modname .. ":log_alive"
local leaves = modname .. ":leaves"
local leaves_growing = modname .. ":leaves_growing"
local leaves_alive = modname .. ":leaves_alive"



local max_grow_distance = 2
local leaves_grow_cost = 250

blockgame.register_increasing_abm({
	id = modname .. ":grow_leaves",
	label = "grow leaves",
	nodenames = {leaves_growing},
	neighbors = {log_alive, leaves_growing, leaves_alive},
	interval = 15,
	chance = 8,
	rate = function (pos, node, data)
		-- TODO: account for nearby nodes? e.g. grow slower if there are more leaves nearby.
		return data.value + math.random(1, 99)
	end,
	check = function (pos, node, data)
		return data.value >= leaves_grow_cost
	end,
	action = function (pos, node, data)
		-- TODO: give leaves energy over time, that they spend when creating new leaves.
		-- this requires the API to add support for increasing ABM `action`:s to modify `data`.
		local meta = minetest.get_meta(pos)
		local distance = meta:get_int("leaf_distance") or 1
		if distance >= max_grow_distance then
			minetest.set_node(pos, {name = leaves_alive})
			return
		end

		local sides = blockgame.vector.get_sides_of(pos)
		for _, target in pairs(sides) do
			if blockgame.chance(2) then
				blockgame.attempt_place(target, {name = leaves_growing})
				-- TODO: find lowest possible leaf distance by checking all 4 sides?
				minetest.get_meta(target):set_int("leaf_distance", distance + 1)
			end
		end
		minetest.set_node(pos, {name = leaves_alive})
	end,
})