Roblox Raycast: Points & Beyond - Detect Collisions!

Raycasting Between Two Points in Roblox: A Simple Guide (No Math Degree Required!)

Okay, so you want to use raycasting in Roblox to detect something between two points. Awesome! It's actually a pretty handy trick. Think of it like firing a laser beam – you tell Roblox where to start the beam, where it should end, and Roblox tells you what (if anything) the beam hits along the way. Cool, right? Let's dive in.

What is Raycasting Anyway? (The Super Quick Version)

Raycasting, at its core, is a way to simulate a line (the "ray") and see if it intersects with anything in your Roblox game world. It's used for tons of things:

  • Weapon systems: Detecting hits from bullets or lasers.
  • AI: Helping NPCs "see" their surroundings and navigate.
  • Player interaction: Checking if a player is looking at an object they can interact with.
  • Terrain analysis: Finding the ground beneath a character's feet.

And that's just scratching the surface! The possibilities are endless. But today, we're focusing on that specific "between two points" scenario.

The Basic Code: Let's Get Our Hands Dirty

First, you'll need two things:

  1. A starting point (origin): Where the ray begins. Think of this as the muzzle of your gun.
  2. An ending point (direction): Where the ray is aiming. This is crucial – you need to tell Roblox which way to fire the ray.

Now, for the code (written in Lua, which Roblox uses):

-- Define the starting and ending points
local startPoint = Vector3.new(0, 5, 0) -- Example: A point in the center of your spawn location
local endPoint = Vector3.new(10, 5, 0) -- Example: 10 studs to the right

-- Calculate the direction vector
local direction = (endPoint - startPoint).Unit -- VERY important to normalize!

-- Calculate the distance the ray should travel
local distance = (endPoint - startPoint).Magnitude

-- Create the ray
local ray = Ray.new(startPoint, direction * distance)

-- Set up raycast parameters (optional but recommended!)
local params = RaycastParams.new()
--Ignore certain instances, like the character firing the weapon
params.FilterType = Enum.RaycastFilterType.Blacklist
--Avoid casting onto the character who is casting the ray
params.FilterDescendantsInstances = {game.Players.LocalPlayer.Character}
params.IgnoreWater = true -- Optional: Ignore water if you don't need to detect it
-- Perform the raycast
local result = workspace:Raycast(startPoint, direction * distance, params)

-- Check if we hit anything
if result then
    print("Raycast hit something!")
    print("Hit position:", result.Position)
    print("Hit instance:", result.Instance)
else
    print("Raycast hit nothing.")
end

Let's break that down, shall we?

  • Vector3.new(x, y, z): This creates a 3D point in space. Replace the example coordinates with your actual start and end points. Remember, Roblox uses studs as its unit of measurement.

  • direction = (endPoint - startPoint).Unit: This is key. We subtract the start point from the end point to get a vector pointing from the start to the end. Then, .Unit normalizes the vector. Normalizing means it makes the vector have a length of 1. Why is this important? Because the Raycast function expects a direction, not a distance. We'll handle the distance separately.

  • distance = (endPoint - startPoint).Magnitude: This calculates the distance between the two points. We'll use this to tell the ray how far to travel in the direction we calculated.

  • *`Ray.new(startPoint, direction distance)`:* This creates the ray itself. The first argument is the starting point, and the second is the direction multiplied by* the distance. This ensures the ray travels the correct distance in the specified direction.

  • *`workspace:Raycast(startPoint, direction distance, params)`:** This is where the magic happens! This function actually performs the raycast. The first argument is the world to raycast through (the workspace), the second and third are the start point, direction and distance, and the final argument is any filtering you need.

  • if result then ...: This checks if the ray hit anything. If result is not nil, it means the ray hit something. We can then access information about what it hit, like its position (result.Position) and the instance itself (result.Instance).

Optimizing Raycasts: Parameters are Your Friends

The RaycastParams object is super important for optimizing your raycasts and preventing unexpected results. Let's look at the most common ones:

  • FilterType: This determines how the raycast should treat the FilterDescendantsInstances list. Enum.RaycastFilterType.Blacklist means the raycast will ignore anything in the list. Enum.RaycastFilterType.Whitelist means the raycast will only hit things in the list.

  • FilterDescendantsInstances: This is a table (a list) of instances that the raycast should either ignore or only hit, depending on the FilterType. This is extremely useful for preventing your raycast from hitting the character that's firing the weapon or anything else you want to avoid.

  • IgnoreWater: Set this to true to make the raycast ignore water. Useful if you're not concerned with detecting water.

Putting it All Together: A Simple Example

Let's say you want to create a laser pointer that shows where the player is looking. You could use the following code in a LocalScript inside StarterPlayerScripts:

local Players = game:GetService("Players")
local RunService = game:GetService("RunService")
local player = Players.LocalPlayer
local mouse = player:GetMouse()

local part = Instance.new("Part")
part.Anchored = true
part.CanCollide = false
part.Size = Vector3.new(0.2, 0.2, 0.2)
part.Shape = Enum.PartType.Ball
part.Material = Enum.Material.Neon
part.Parent = workspace

RunService.RenderStepped:Connect(function()
    local startPoint = mouse.Origin.Position
    local endPoint = mouse.Hit.Position

    local direction = (endPoint - startPoint).Unit
    local distance = (endPoint - startPoint).Magnitude

    local params = RaycastParams.new()
    params.FilterType = Enum.RaycastFilterType.Blacklist
    params.FilterDescendantsInstances = {player.Character} -- Filter out the player's character
    params.IgnoreWater = true

    local result = workspace:Raycast(startPoint, direction * distance, params)

    if result then
        part.Position = result.Position
    else
        part.Position = endPoint
    end
end)

This script creates a small, bright sphere and moves it to where the player's mouse is pointing. It uses raycasting to ensure the sphere sticks to surfaces, even if the mouse is pointing through them. Cool, huh?

Common Pitfalls and How to Avoid Them

  • Forgetting to Normalize: This is the most common mistake. If you don't normalize the direction vector, your raycast will travel the wrong distance and might hit the wrong thing (or nothing at all!).
  • Filtering Issues: Make sure your FilterDescendantsInstances table is correct. Accidentally filtering out the wrong objects can lead to weird behavior.
  • Performance: Raycasting can be computationally expensive, especially if you're doing it every frame. Try to limit the number of raycasts you perform and optimize your code as much as possible. Consider using a shorter ray distance if you only need to detect things within a limited range.
  • Incorrect Start and End Points: Make sure you're using the correct starting and ending points for your raycast. A small error in the position can cause the ray to miss its target.

So there you have it! Raycasting between two points in Roblox isn't as scary as it might seem. With a little practice, you'll be using it to create all sorts of cool and interesting game mechanics. Now go forth and create something awesome!