Tag: Roblox

Click here for part 2 of this tutorial series. In part 2, we created a simple solution to our problem of creating an event system. We saw there are some problems with this, namely the synchronous execution. One after another, our connected functions are called when the event is fired.

Often times, when you’re using a game engine it’s best to let the engine do the heavy lifting for you. Roblox provides the BindableEvent object to create events in (or out of) the game hierarchy, however it isn’t often that you’ll want to instantiate one every time you want to create a custom event. Let’s create an Event class which uses BindableEvent internally intstead. Let’s re-start with the boilerplate from part 2:

-- A new Event class that uses BindableEvent internally
local Event = {}
Event.__index = Event

function Event.new()
	local self = setmetatable({
		bindableEvent = Instance.new("BindableEvent");
	}, Event)
	return Event
end

We’re no longer keeping track of the connections ourselves with a table. We’ll merely be passing the connect and fire behaviors onto the already existing functionality of the object. This is quite simple, actually:

function Event:connect(func)
	return self.bindableEvent.Event:connect(func)
end

function Event:fire(...)
	self.bindableEvent:Fire(...)
end

The key benefit here: since we’re delegating the responsibility of calling the connected functions to the BindableEvent, it can handle the threading as well. Connected functions that yield will not block other connected functions, so this is a primary benefit from the first simple solution. Note the use of …  to represent “any and all variables passed to this function”. We’ll talk more about it in part 4.

There is still a problem with this, though. BindableEvents were originally created for inter-script communication. When it comes to tables, there’s some “gotchas”

Avoid passing a mixed table (some values indexed by number and others by key), as only the data indexed by number will be passed.

BindableEvent documentation

This is a big drawback to using a BindableEvent. Your tables will not be the same table as the one you fired the event with. Here’s an example demonstrating this drawback:

local event = Event.new()
local my_table = {}

local function onEvent(other_table)
	error(other_table == my_table, "Fail whale!")
end

event:connect(onEvent)
event:fire(my_table)

You can see that we are firing the event with my_table , then in the connected function comparing that table to (supposedly) itself. This shouldn’t ever throw an error, but it always does due to the described limitations of the BindableEvent.

You’ll also lose metatables, too! So if you created an object using our object-oriented tricks from the previous tutorial, you won’t have an object anymore. Just an empty shell of a table, no purpose, no meaning in life… definitely something you want to avoid.

You can see that the key benefit of letting Roblox handle the threading with the cost of the BindableEvent’s limitations is definitely a trade-off. You can download the finished version of this Event class here. Is it possible to work around this limitation? Maybe. Click here to find out in part 4.

Click here for part 1 of this tutorial series. You should be familiar with the content discussed in my Object-Oriented Programming tutorial.

In part 1, I discussed the pattern of an event system and the need for it in Roblox code. We frequently find ourselves needing to define our own gameplay defined events. Let’s dive into a simple way we can implement this pattern. Let’s use the OOP tricks we know in Lua to create the shell of an Event class.

-- A shell of an event class
local Event = {}
Event.__index = Event

function Event.new()
	local self = setmetatable({
		-- We'll put any variables (fields) we need here
	}, Event)
	return Event
end

function Event:connect(func)
	-- Somehow keep track of the functions connected here
	-- Provide a means to disconnect this function from this event
end

function Event:fire(...)
	-- Call all the functions somehow
end

So, at surface level we need a way to store some number of functions. We should be able to add/remove those functions. Crazy idea: let’s just use a numerically-indexed table of functions. We’ll use table.insert  to connect a function, and to disconnect we’ll iterate over each index and remove the first we find that matches. When we fire the event, just iterate over the list of functions, calling them in order. Let’s code it up.

First, let’s add a connections  table to our event. This will be our table of functions.

function Event.new()
	local self = setmetatable({
		connections = {};
	}, Event)
	return self
end

Next, let’s write the fire function. Simple iteration using a numeric for-loop:

function Event:fire(...)
	for i = 1, #self.connections do
		self.connections[i](...)
	end
end

That oughta do it! Finally, let’s write the connect function.

function Event:connect(func)
	if not func then error("connect(nil)", 2) end
	table.insert(self.connections, func)
end

Notice how I added a line that will throw an error if we sent no function to connect. Finally, we need to add a means to disconnect. Let’s return a table with a disconnect function as a key:

function Event:connect(func)
	if not func then error("connect(nil)", 2) end
	table.insert(self.connections, func)
	
	local function disconnectFunc()
		for i = 1, #self.connections do
			if self.connections[i] == func then
				table.remove(self.connections, i)
				break
			end
		end
	end
	return {disconnect = disconnectFunc}
end

And there we have it! We’ll soon find out that there are some issues with this. For simple uses cases, this works fine. However, if any connected functions yield (yielding essentially means waiting, like announceGameOver does to display the message), the next connected function will not run until the yielding function completes. This is a problem in the part 1 example because we might want our map to clean up first, then the game to announce the final score. It depends on the order in which we connected our events.

This event system calls connected functions in the order they were connected. In other words, first-in-first-out (FIFO). We could reverse this order (last-in-first-out, LIFO) by iterating backwards in the fire function:

function Event:fire(...)
	for i = #self.connections, 1, -1 do
		self.connections[i](...)
	end
end

Alternatively, we could just insert new functions at the beginning of the list in connect by specifying index 1 as the insertion point in the table.insert  call:

table.insert(self.connections, 1, func)

This is actually less efficient as Lua must move all the existing functions in the table over by 1 to make room for the one we’re inserting. For the computer science nerds in the audience, this is an O(n) operation. Simply inserting to the end of the list would be O(1). It goes without saying that making both of these changes (reverse iteration and insertion at the front of the list) would cancel each other out and we’d be back to original behavior of FIFO.

If this solves your problem, then I have good news: you can stop here. As for the rest of us, we have more options to explore in part 3. You can download the finished version of this Event class here.

Click here to advance to part 3 of this tutorial series.

Hey everyone. Lately I’ve been considering the many ways to create event systems for Roblox Lua. You may already be familiar with native events, a.k.a. RBXScriptSignal, in Roblox. You connect your function to one of these, and when the engine detects the occurrence, it calls your function with the relevant arguments. BasePart.Touched is one of the most common examples.

But what if you’re making your own objects, like in my object-oriented programming tutorial? If your custom objects want to define events, you have a ton of different options for implementing this pattern. In this tutorial series, I will explore the different methods you can use to implement an event-listener pattern.

Before we look at the different ways we could create a system like this, let’s define exactly what we’re trying to code up. We want to be able to create an event and connect any number of functions to it. In addition, we want to send arguments to the connected functions when this event is fired. Finally, we need to be able to disconnect a connected function from this event. So, no matter what systems we end up making, we should be able to do something like this (for example, in a round-based game):

local function announceGameOver(finalScore)
	print("Game over!")
	local message = Instance.new("Message")
	message.Text = "Game over! Your score: " .. finalScore
	message.Parent = workspace
	wait(2)
	message:Destroy()
end

local function cleanUpTheGame()
	-- Destroy the map if we have one
	if workspace:FindFirstChild("Map") then
		workspace.Map:Destroy()
	end
	-- Clean up any debris on the ground
	while workspace:FindFirstChild("Debris") do
		workspace.Debris:Destroy()
	end
end

local onGameOver = Event.new()
onGameOver:connect(announceGameOver)
onGameOver:connect(cleanUpTheGame)

-- ...somewhere else in your code...
onGameOver:fire(69)

A couple things to note:

• It ought not matter in which order our functions announceGameOver and cleanUpTheGame will run; in a perfect world we’d have them happen at the same time. (In reality, one will always happen before the other and it’s the order in which we connect these functions that may ultimately play a part in what order they are actually called.)
• Not all connected functions will need to use all the arguments sent by the event, such as cleanUpTheGame  not needing the final score we sent.
• Not all connected functions will need to stay connected – we might need to disconnect functions as a cleanup measure.
• For brevity, I will be skipping over writing a wait method to yield until an event is fired.

With those things in mind, let’s see the different ways we can make event systems in Roblox Lua!

Click here to proceed to part 2 of this tutorial series.

Hi everyone! This is going to be a tutorial on scripting dice using Roblox Studio. Let’s start by creating the dice model.

Creating the Dice Model

If you’re already comfortable using Roblox Studio to build things, you can skip this part and grab the Model off Roblox here.

1. Create a 4×4 part.
2. Color the dice white. Set the Top and Bottom surfaces to Smooth.
3. Add the following decals: Top (3), Bottom (4), Front (1), Back (6), Left (2), Right (5). Credit to game-icons.net for the dice face images. Remember, opposite face values of a dice will add to 7.
4. Add a new Script to the part, as well as a StringValue named Face and an IntValue named Roll. We’ll use these as the output for our script.

Scripting the Dice

Now for the fun part. Let’s start by getting some variable references to the objects in the game hierarchy (visible in the Explorer window). Remember to open the Output window when scripting! Small note: Unless otherwise mentioned, the given code should be added from top to bottom in the script.

local dice = script.Parent
local vFace = dice.Face
local vRoll = dice.Roll

Next, let’s define a function called getHighestFace(part) which will determine the highest face of given part and return it.

local function getHighestFace(part)
	local highestFace
	local height = -math.huge
	
	-- For each NormalId (Top, Bottom, Front, Back, Left, Right)
	for k, normalId in pairs(Enum.NormalId:GetEnumItems()) do
		local y = part.CFrame:pointToWorldSpace(Vector3.FromNormalId(normalId)).y
		if y > height then
			highestFace = normalId
			height = y
		end
	end
	
	return highestFace
end

What’s going on here: We’re going over each NormalId (Top, Bottom, Left, etc). For each of these, we get a Vector3 value from the NormalId using Vector3.FromNormalId so Top translates to (0, 1, 0), Bottom is (0, -1, 0), etc. Then we’re transforming that point, which is a point local to the given part’s CFrame, into world space using pointToWorldSpace. Finally, we’re getting the Y component (height) of the resulting world point.

The rest of the this function is simply finding the face that gives the highest world point. There’s the meat of the program – now let’s hook it up into something practical by writing an update function that uses the getHighestFace function.

local function update()
	local highestFace = getHighestFace(dice)
	vFace.Value = highestFace.Name
end

This is simple enough: get the highest face of the dice, then stuff it into the Face StringValue. We’ll revisit this function later to determine what number is on what side of the dice. For now, we’ll use this line to connect the update function with the RunService‘s Stepped event, which fires about 30 times a second when the game is unpaused.

game:GetService("RunService").Stepped:connect(update)

You could also add a while-true-do loop and update on your own frequency if you wanted. Test your script by pressing play, then rotating your dice. If the Face StringValue’s Value changes accurately based on the highest face, then you’ve done got the basis of your dice! If not, check the Output window for any red error messages or yellow warnings. One little typo can mess up the entire script!

If your dice is working properly, let’s go back and update the update function so that it determines which number is on what side of the dice. Add this to the top of your script:

local faceValues = {
	Front = 1; Back = 6;
	Left = 2; Right = 5;
	Top = 3; Bottom = 4;
}

This is a table we’ll use to look up values of the dice decals that are on whatever side of the part is highest. Update your update function to this:

local function update()
	local highestFace = getHighestFace(dice)
	vFace.Value = highestFace.Name
	vRoll.Value = faceValues[vFace.Value]
end

This will stuff the current face’s value into the Roll IntValue. This way, another script in your game could read the current dice roll without having to do any math.

And that’s it! Go ahead and play around with your dice in Play mode and make sure each side corresponds to the correct value. If not, you might have to switch some values in the faceValues table. If none of your values are changing, check the Output for errors.

Here’s the completed dice model in case you got stuck or lost.