Learn How To Raycast Downwards Roblox (Quick Guide)

How to Raycast Downwards in Roblox: Stop Falling Through the Floor!

Alright, so you're trying to make your Roblox game, and you're running into that classic problem: your player's just…falling through the floor. Annoying, right? The solution, my friend, is raycasting! Specifically, raycasting downwards. Let's dive into how to do it.

What's a Raycast Anyway?

Before we get into the how, let's briefly cover the what. Think of a raycast as an invisible laser beam (or, y'know, a line) that you shoot out from a point in a specific direction. When that beam hits something, the raycast returns information about what it hit, like the part, the point of impact, and the normal (the direction the surface is facing).

In our case, we're going to shoot this beam downwards from our player. If it hits the ground, we know we're good. If it doesn't, we know we're about to fall through the world and need to do something about it.

The Basic Raycast: The Code

Okay, enough chit-chat, let's get to the code. This is the core of how to raycast downwards in Roblox. We're going to use the Workspace:Raycast() function.

local character = script.Parent -- Assuming this script is inside the character
local humanoidRootPart = character:WaitForChild("HumanoidRootPart")
local params = RaycastParams.new()
params.FilterType = Enum.RaycastFilterType.Blacklist
params.FilterDescendantsInstances = {character} -- Important to prevent hitting yourself!

local rayOrigin = humanoidRootPart.Position
local rayDirection = Vector3.new(0, -5, 0) -- Downwards! Change the number for ray length

local raycastResult = workspace:Raycast(rayOrigin, rayDirection, params)

if raycastResult then
    -- We hit something!
    local hitPart = raycastResult.Instance
    local hitPosition = raycastResult.Position
    print("Raycast hit: " .. hitPart.Name .. " at " .. hitPosition)

    -- Do something here! Like stick the player to the ground
else
    -- We didn't hit anything!
    print("Raycast didn't hit anything!")

    -- Do something here! Like start falling, or stop moving
end

Let's break this down:

local character = script.Parent: We're getting the character model that this script is inside. This assumes the script is placed directly inside your character model (e.g., inside the StarterCharacterScripts folder).
local humanoidRootPart = character:WaitForChild("HumanoidRootPart"): We're finding the HumanoidRootPart of the character, which is usually at the base of the humanoid. This is a crucial part for raycasting from the correct position. We use WaitForChild just in case it takes a moment for the root part to load.
local params = RaycastParams.new(): This creates a RaycastParams object. This lets us configure how the raycast behaves, like what to ignore.
params.FilterType = Enum.RaycastFilterType.Blacklist: We're telling the raycast to ignore certain things.
params.FilterDescendantsInstances = {character}: This is super important! It makes the raycast ignore the character itself. If you don't do this, the raycast will almost always hit the character first, and you won't be able to detect the ground.
local rayOrigin = humanoidRootPart.Position: This sets the starting point of the raycast to the character's root part's position.
local rayDirection = Vector3.new(0, -5, 0): This defines the direction of the raycast. (0, -5, 0) means "straight down" for 5 studs. Adjust the 5 to change the ray's length. Shorter rays are more precise but might miss the ground if the character is slightly off. Longer rays are more forgiving but might hit the ground further away.
local raycastResult = workspace:Raycast(rayOrigin, rayDirection, params): This is the actual raycast! It shoots the ray and returns a result. It can return nil if it doesn't hit anything.
if raycastResult then: This checks if the raycast hit something. If it did, raycastResult will contain information about the hit.
local hitPart = raycastResult.Instance: Gets the part the raycast hit.
local hitPosition = raycastResult.Position: Gets the position where the raycast hit the part.
else: If the raycast didn't hit anything, raycastResult will be nil, and this block of code will execute.

Making it Work: Keeping Your Player On the Ground

That's the raycast itself. Now, how do we use it to actually keep our player on the ground? There are a few approaches, and the best one depends on your game's needs.

Simple Approach: Changing Humanoid State

One of the simplest methods is to modify the Humanoid's state when the raycast doesn't hit.

-- Inside the "else" block (raycast didn't hit)
character.Humanoid:ChangeState(Enum.HumanoidStateType.Freefall) -- Make them fall!

And in the if raycastResult then block, you could potentially set the state back to something like Running or Standing if you need specific animations. This can be pretty effective for simple platformers.

More Advanced: Applying a Force

A more robust approach involves using forces to keep the player grounded. This is especially useful if you want more control over the player's movement and physics.

-- Inside the "else" block (raycast didn't hit)
local forceToApply = Vector3.new(0, 200, 0) -- Upwards force! Adjust the value as needed
humanoidRootPart:ApplyImpulse(forceToApply)

This code applies an upward force to the HumanoidRootPart. You'll need to experiment with the 200 value to find a good balance that keeps the player grounded without making them jittery.

Why apply an impulse instead of a force? Because an impulse is a one-time force, while a regular force is applied continuously. Applying a continuous force would cause the player to just float up into the sky!

Important: Running This Regularly

Crucially, you need to run this raycast every frame or at least very frequently (e.g., every 0.03 seconds). You can do this using RunService.Heartbeat:Connect(function() ... end).

local RunService = game:GetService("RunService")

RunService.Heartbeat:Connect(function()
    -- All the raycast code goes here!
    local character = script.Parent
    local humanoidRootPart = character:WaitForChild("HumanoidRootPart")
    -- ... the rest of the raycast code from above ...
end)

This ensures that the raycast is constantly checking for the ground and reacting accordingly. Without this, your player will only stay grounded for a split second.

Troubleshooting and Tips

Raycast Length: Adjust the length of the raycast (Vector3.new(0, -5, 0)) to suit your game. Too short, and it'll miss the ground. Too long, and it might hit something unintended.
Filtering: The RaycastParams are your best friend! Make sure you're filtering out the character correctly and potentially other objects that might interfere with the raycast.
Performance: Raycasts can be a bit expensive if you're doing tons of them every frame. Optimize your code and consider reducing the frequency of the raycasts if you're experiencing performance issues. Only raycast when the character is actually moving, for example.
Collision Groups: Explore using collision groups to further refine which objects your raycast can hit. This can be helpful for complex environments.
Visual Debugging: Use DebugService to visually draw the raycast in the world for troubleshooting:
```
local DebugService = game:GetService("DebugService")
DebugService:DrawLine(rayOrigin, rayOrigin + rayDirection, Color3.new(1,0,0), 1) -- Red line
```
This helps you see where the raycast is going and what it's hitting (or not hitting!).

And there you have it! You now know how to raycast downwards in Roblox and (hopefully) keep your player firmly on the ground. Good luck with your game development! Remember to experiment and tweak the code to fit your specific needs. Have fun!