make leaves growth use an increasing ABM.

this also means that leaves now grow slower.

mods/bg_tree/grow_leaves.lua

@@ -7,19 +7,28 @@ local leaves = modname .. ":leaves"
 local leaves_growing = modname .. ":leaves_growing"
 local leaves_alive = modname .. ":leaves_alive"
 
--- END OF NODE NAMES
+
 
 local max_grow_distance = 2
+local leaves_grow_cost = 250
 
--- TODO: turn this into an increasing ABM.
-blockgame.register_abm({
+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,
-	action = function (pos, node)
+	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 return end
@@ -28,6 +37,7 @@ blockgame.register_abm({
 		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