Debounce

A debounce system is a set of code that keeps a function from running too many times. It comes from the idea of mechanical switch bounce, where a switch bounces when pushed, creating multiple signals. In the context of Roblox, this problem occurs mainly with the Touched event, when a part touches another multiple times in a short space of time, but may be useful in other cases as well.

Theory[edit]

Let's say you have a button on the floor. When you jump on the button, it prints a message to the output. Your code would look like this:

game.Workspace.Button.Touched:Connect(function(hit)
    print("Button pressed") --Print the message
    wait(1)                 --Wait for 1 second
    print("Hi :D")          --Print another message
end)


This will put this message in the output:

Button pressed
Hi :D


The problem is that because of the way the physics engine handles the collision, it will not register just one collision, but may cause several Touched events to fire, so your output will look more like this:

Button pressed
Button pressed
Button pressed
Button pressed
Button pressed
Hi :D
Hi :D
Hi :D
Hi :D
Hi :D


Rather than executing sequentially, all the event handlers execute at the same time.

Here is a possible scenario you may encounter:

If you're using a button to regenerate a model then it will make 5 of whatever you are regenerating. This is an issue because all 5 will be in the same spot causing all kinds of problems. This can problem can easily be avoided by using a simple debounce system in your code. Of course, you could use a ClickDetector for your button, which would correct the problem, but you can't always use ClickDetectors, so sometimes, a debounce would be useful.

This is how a basic debounce system works:

When an action happens, such as someone pressing your floor button, the script locks any new function calls until a time passes or the action is complete.

Use case[edit]

It's fairly simple to convert an existing script to using debounce. Let's use the same script we had above, and add a couple of lines. In this case we will put in a time limit to wait for until the function can be run again.

Select
local buttonPressed = false
--Store whether the button is pressed in a local variable
 
Workspace.Button.Touched:Connect(function(hit)
    if not buttonPressed then
    -- Is it not pressed?
 
        buttonPressed = true
        -- Mark it as pressed, so that other handlers don't execute
 
        print("Button pressed")
        wait(1)
        print("Hi :D")
        -- Do Stuff
 
        buttonPressed = false
        -- Mark it as not pressed, so other handlers can execute again
    end
end)


This will cause your output to look like this:

Button pressed
Hi :D


That's more like it! You can use this same concept, by adding the same 4 lines to different scripts, in most any script involving functions. It doesn't even have to just be touched objects, it can be used to keep people from pressing a button more than once, firing a weapon more often than you want, or preventing a new event from happening before the old one is done. Take a look at the next example.

Real world[edit]

Here's the Local Gui script of the Rocket Launcher tool:

Select
enabled = true
mouse.Button1Down:Connect(function()
    if not enabled then
        return
    end
 
    enabled = false
    mouse.Icon = "rbxasset://textures\\GunWaitCursor.png"
 
    wait(12)
    mouse.Icon = "rbxasset://textures\\GunCursor.png"
    enabled = true
 
end)


When you fire a rocket, the script shows the reload icon. Then the function waits for 12 seconds. During this time, enabled is false, so if the player tries to fire another rocket, the script won't run because the function will just return right away. After the 12 seconds are up, the reload cursor goes away and enabled becomes true again, allowing the user to fire another rocket.

Advanced notation[edit]

After a while, it might get tedious defining a separate debounce variable for each event handler. Instead, you can write a debounce function, that returns a debounced copy of an event handler. This uses the ... notation to forward arguments.

Select
function debounce(func)
    local isRunning = false    -- Create a local debounce variable
    return function(...)       -- Return a new function
        if not isRunning then
            isRunning = true
 
            func(...)          -- Call it with the original arguments
 
            isRunning = false
        end
    end
end


Applying this to the original code:

Select
Workspace.Button.Touched:Connect(debounce(function(hit)
    print("Button pressed") --Print the message
    wait(1)                 --Wait for 1 second
    print("Hi :D")          --Print another message
end))


Practice[edit]

Exercise

Instructions

Make a part that lowers the player’s health by 5 when touched. Use debounce to only allow the player to be hurt by the part every 3 seconds.

Solution
Select
local buttonPressed = false
--Store whether the button is pressed in a local variable
 
script.Parent.Touched:connect(function(hit)
    if not buttonPressed then
    -- Is it not pressed?
 
        buttonPressed = true
        -- Mark it as pressed, so that other handlers don't execute
 
		if hit.Parent then
			hum = hit.Parent:FindFirstChild("Humanoid")
			hum.Health = hum.Health - 5
		end
        wait(3)
 
        buttonPressed = false
        -- Mark it as not pressed, so other handlers can execute again
    end
end)