create grass mod.

create a new mod that implements basic grass growth and death.

mods/bg_api/init.lua

@@ -10,3 +10,4 @@ load_file("utils_node")
 load_file("utils_stringify")
 load_file("utils_random")
 load_file("utils_vector")
+load_file("wrapper_abm")

mods/bg_api/utils_node.lua

@@ -8,3 +8,19 @@ function blockgame.reg_simple_node (name, desc, groups)
 		groups = groups,
 	})
 end
+
+-- probably temporary; will probably use groups for this later.
+local air_flowable = {
+	"air",
+	"tree:leaves",
+	"tree:leaves_alive",
+}
+
+function blockgame.air_flows_through (pos, node)
+	node = node or minetest.get_node(pos)
+	local node_name = node.name
+	for _, name in pairs(air_flowable) do
+		if name == node_name then return true end
+	end
+	return false
+end

mods/bg_api/utils_vector.lua

@@ -1,6 +1,8 @@
 blockgame.vector = blockgame.vector or {}
 local api = blockgame.vector
 
+-- TODO: replace direct sharing of api variables such as `sides` with functions that return them, to prevent other mods from mutating the shared data.
+
 api.horizontal_directions = {
 	west = vector.new(-1, 0, 0),
 	east = vector.new(1, 0, 0),

mods/bg_api/wrapper_abm.lua

@@ -0,0 +1,3 @@
+function blockgame.register_abm (...)
+	return minetest.register_abm(...)
+end

mods/bg_grass/death.lua

@@ -0,0 +1,10 @@
+blockgame.register_abm({
+	nodenames = {"core:grass"},
+	interval = 15,
+	chance = 4,
+	action = function (pos, node)
+		if blockgame.air_flows_through(pos + blockgame.vector.dirs.up) then return false end
+		minetest.set_node(pos, {name = "core:dirt"})
+		return true
+	end,
+})

mods/bg_grass/growth.lua

@@ -0,0 +1,23 @@
+blockgame.register_abm({
+	nodenames = {"core:grass"},
+	neighbors = {"core:dirt"},
+	interval = 15,
+	chance = 8,
+	action = function (pos, node)
+		-- TODO: also check diagonally adjacent nodes?
+		-- TODO: shuffle sides; currently they grow in a specific order determined by the order of `blockgame.vector.sides`.
+		local sides = blockgame.vector.sides
+		for _, side in pairs(sides) do
+			if attempt_spread(pos + side) then return true end
+		end
+		return false
+	end,
+})
+
+function attempt_spread (pos)
+	if minetest.get_node(pos).name ~= "core:dirt" then return false end
+	if not blockgame.air_flows_through(pos + blockgame.vector.dirs.up) then return false end
+
+	minetest.set_node(pos, {name = "core:grass"})
+	return true
+end

mods/bg_grass/init.lua

@@ -0,0 +1,2 @@
+load_file("growth")
+load_file("death")

mods/bg_grass/mod.conf

@@ -0,0 +1,3 @@
+name = grass
+description = adds grass spreading and related mechanics to blockgame.
+depends = core, api