refactor grass spreading and related api function.

mods/bg_api/util_node.lua

@@ -13,11 +13,10 @@ end
 
 function blockgame.air_flows_through (pos, node)
 	node = node or minetest.get_node(pos)
-	local node_name = node.name
-
-	if node_name == "air" then return true end
-
-	return minetest.get_item_group(node_name, "air_flowable") > 0
+	return blockgame.item_matches(node.name, {
+		"air",
+		"group:air_flowable",
+	})
 end
 
 

mods/bg_terrain/grass_grow.lua

@@ -48,7 +48,10 @@ blockgame.register_abm({
 })
 
 function attempt_spread (pos)
-	if minetest.get_node(pos).name ~= "bg_terrain:dirt" then return false end
+	local name = minetest.get_node(pos).name
+
+	if not blockgame.item_matches(name, {"group:grassable"}) then return false end
+
 	if not blockgame.air_flows_through(pos + blockgame.vector.dirs.up) then return false end
 
 	minetest.set_node(pos, {name = "bg_terrain:grass"})

mods/bg_terrain/node.lua

@@ -34,6 +34,7 @@ blockgame.register_node(modname .. ":grass", {
 blockgame.reg_simple_node("dirt", "Dirt", {
 	cracky = 3,
 	dirty = 1,
+	grassable = 1,
 })
 
 blockgame.register_loose_version(modname .. ":dirt")