--To add a new smooth node you have to define the node also

--the node that will be checked for corresponding BOTTOM_NODE
local NODE = { 
    "default:dirt",
    "default:dirt_with_grass",
    "default:cobble",
    "default:wood",
    "default:tree",
}

-- the node below the checked NODE
local BOTTOM_NODE = {
    "default:stone",
    "default:stone",
    "default:stone",
    "default:dirt",
    "default:dirt"
}

-- the node to which it will change
local NEW = {
    "smooth:dirt_stone",
    "smooth:dirt_stone",
    "smooth:cobble_stone",
    "smooth:wood_grass",
    "smooth:tree_grass",
}

-- if we should change the top or bottom node
local TOP = {
    "false",
    "false",
    "false",
    "true",
    "true",
}

--register abm for node changes
for i, node in ipairs(NODE) do
    minetest.register_abm({
		nodenames = {NODE[i]},
		interval = 30,
		chance = 3,
		action = function(pos)
			local bottom = {x=pos.x, y=pos.y-1, z=pos.z}
			local node = minetest.env:get_node(bottom)
			
			if (node.name==BOTTOM_NODE[i]) then
				if TOP[i] == "false" then
					minetest.env:remove_node(bottom)
					minetest.env:add_node(bottom, {name=NEW[i]})
				else
					minetest.env:remove_node(pos)
					minetest.env:add_node(pos, {name=NEW[i]})
				end
			end
		end
	})
end

--define the nodes
minetest.register_node("smooth:dirt_stone", {
	description = "Dirt Stone",
	tile_images = {"smooth_dirt_stone_top.png", "default_stone.png", "default_stone.png^smooth_dirt_stone.png"},
	is_ground_content = true,
	groups = {cracky=3},
	drop = 'default:cobble',
	sounds = default.node_sound_stone_defaults(),
})
minetest.register_node("smooth:cobble_stone", {
	description = "Cobble Stone",
	tile_images = {"smooth_cobble_stone_top.png", "default_stone.png", "default_stone.png^smooth_cobble_stone.png"},
	is_ground_content = true,
	groups = {cracky=3},
	drop = 'default:cobble',
	sounds = default.node_sound_stone_defaults(),
})
minetest.register_node("smooth:wood_grass", {
	description = "Wood Grass",
	tile_images = {"default_wood.png", "default_wood.png", "default_wood.png^smooth_grass.png"},
	is_ground_content = true,
	drop = 'default:wood',
	groups = {snappy=1,choppy=2,oddly_breakable_by_hand=2,flammable=3},
	sounds = default.node_sound_wood_defaults(),
})
minetest.register_node("smooth:tree_grass", {
	description = "Tree Grass",
	tile_images = {"default_tree_top.png", "default_tree_top.png", "default_tree.png^smooth_grass.png"},
	is_ground_content = true,
	groups = {tree=1,snappy=1,choppy=2,oddly_breakable_by_hand=1,flammable=2},
	sounds = default.node_sound_wood_defaults(),
	drop = 'default:tree',
})

minetest.log("action", "[MOD]"..minetest.get_current_modname().." -- loaded from "..minetest.get_modpath(minetest.get_current_modname()))