initial working commit

.gitignore

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+*.swp

depends.txt

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+default

init.lua

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+unstablenodes = {}
+
+local unstabledepth = 3
+local unstablerange = 5
+local falldelay = 0.1
+
+local function is_unstable(nodename)
+
+	minetest.debug("Checking "..nodename )
+	return (minetest.get_item_group(nodename, "unstable") > 0)
+end
+
+local function can_fall_through(nodename)
+	return minetest.registered_nodes[nodename].buildtable_to or nodename == "air"
+end
+
+local function monitor_fall(obj)
+	minetest.after(0.2, function()
+		if math.abs(obj:getvelocity().y) > 0 then
+			monitor_fall(obj)
+		else
+			local nodename = obj:get_luaentity().name
+			local pos = obj:getpos()
+			obj:remove()
+			minetest.set_node(pos, {name=nodename})
+		end
+	end)
+end
+
+local function add_unstable_node(pos, nodename)
+	if minetest.registered_entities[nodename] then
+		local obj = minetest.add_entity(pos, nodename)
+		local luae = obj:get_luaentity()
+		if luae then
+			obj:setvelocity({x=0, y= -luae.fallspeed, z=0})
+			monitor_fall(obj)
+			return true
+		else
+			obj:remove()
+			return false
+		end
+	end
+end
+
+local function entityfall(pos)
+	local node = minetest.get_node(pos)
+	minetest.debug("Falling "..minetest.pos_to_string(pos))
+
+	-- Remove node
+	minetest.remove_node(pos)
+
+	-- Add entity
+	return add_unstable_node(pos, node.name)
+
+end
+
+local function fallunstable(pos, limit)
+	if not limit then
+		limit = unstabledepth
+	end
+	minetest.debug("Limit: "..tostring(limit) )
+
+	if limit < 1 then
+		return false
+	end
+
+	local node = minetest.get_node(pos)
+
+	if not is_unstable(node.name) then
+		return false
+	end
+
+	local posunder = {x = pos.x, y = pos.y - 1, z = pos.z}
+	local posover = {x = pos.x, y = pos.y + 1, z = pos.z}
+	
+	local undernode = minetest.get_node(posunder)
+	if not is_unstable(undernode.name) and not can_fall_through(undernode.name) then
+		return false
+
+	elseif can_fall_through(undernode.name) then
+		minetest.after(falldelay * (limit-1), function()
+			entityfall(pos)
+		end)
+		return true
+	else
+		minetest.log("error","unexpected condition on unstable ground")
+	end
+	return false
+end
+
+minetest.register_on_punchnode(function(pos, node, puncher, pointed_thing)
+	if is_unstable(node.name) then
+		local unodes = minetest.find_nodes_in_area(
+			{x=pos.x-unstablerange, y=pos.y-unstabledepth, z=pos.z-unstablerange},
+			{x=pos.x+unstablerange, y=pos.y, z=pos.z+unstablerange},
+			{"group:unstable"}
+		)
+		for _,thepos in pairs(unodes) do
+			fallunstable(thepos)
+		end
+	end
+end)
+
+function unstablenodes.define_unstable_node(nodename, fallspeed)
+	local tileset = minetest.registered_nodes[nodename].tiles
+	if type(tileset) == "string" then
+		tileset = {tileset}
+	end
+	local newtileset = {}
+
+	for k,v in pairs(tileset) do
+		if type(v) == "table" then
+			newtileset[k] = v.name
+		else
+			newtileset[k] = v
+		end
+	end
+
+	minetest.debug(dump(newtileset))
+	while #newtileset < 6 do
+		newtileset[#newtileset+1] = newtileset[#newtileset]
+	end
+
+	local def = {
+		name = nodename,
+		textures = newtileset,
+		visual = "cube",
+		visual_size = {x = 1, y = 1},
+		collisionbox = {-0.5, -0.5, -0.5, 0.5, 0.5, 0.5},
+		fallspeed = fallspeed or 10,
+		physical = true,
+		on_activate = function(self)
+			monitor_fall(self.object)
+		end
+	}
+
+	minetest.register_entity(nodename, def)
+end
+
+function unstablenodes.add_unstable_version(nodename)
+	local newdirtdef = {}
+	local newnodename = "unstablenodes:"..nodename:gsub(":","_")
+	local oldnodedef = minetest.registered_nodes[nodename]
+	if oldnodedef then
+		for k,v in pairs(oldnodedef) do
+			newdirtdef[k] = v
+		end
+		newdirtdef.groups.unstable = 1
+		newdirtdef.description = "Unstable "..newdirtdef.description
+
+
+		minetest.register_node(newnodename,newdirtdef)
+		unstablenodes.define_unstable_node(newnodename)
+
+		minetest.register_craft({
+			output = newnodename,
+			type = "shapeless",
+			recipe = {nodename, "group:falling_node"}
+		})
+	else
+		minetest.log("error","Could not register an unstable version of non-existent node "..nodename)
+	end
+end
+
+unstablenodes.add_unstable_version("default:cobble")
+unstablenodes.add_unstable_version("default:dirt_with_grass")
+minetest.register_alias("unstablenodes:unstable_dirt","unstablenodes:default_dirt_with_grass")

mod.conf

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+name = unstablenodes