How does this segment of code work?

[simplyjustbased]

ive most likely asked this question before a long time ago but i keep coming back to this segment of code because it works to well

can someone explain what this part of the code does?, im lost trying to understand how some of it works

	local Rv = MPos.Direction * 300
	local Ray1 = workspace:Raycast(MPos.Origin, (Rv * Distance), Params)
	
	local HitPos = if Ray1 then Ray1.Position else (MPos.Origin + Rv)
	local AimAt = (HitPos - FirePoint.WorldPosition)
	
	local BulletRay = workspace:Raycast(FirePoint.WorldPosition, AimAt * 2, Params)
	local ThingHit = if BulletRay then BulletRay.Instance else nil
	local PosHit = if BulletRay then BulletRay.Position else HitPos

full code

repeat task.wait() until game:IsLoaded() and script.Parent:FindFirstChild("Remotes")

-- Variables
local Player = game:GetService('Players').LocalPlayer
local UserInputService = game:GetService("UserInputService")
local RunService = game:GetService("RunService")
local Ts = game:GetService("TweenService")
local Debris = game:GetService("Debris")

local Tool = script.Parent
local RemotesFolder = Tool.Remotes
local RSRemotesFolder = game.ReplicatedStorage.Remotes
local Mesh = Tool.GlockMesh
local Handle = Tool.Handle
local BulletPoint = Mesh.BulletPoint
local CTS = RemotesFolder.ClientToServer
local ClientBullet = RSRemotesFolder.ClientBullet
local BulletFolder = game.ReplicatedStorage.Bullets
local FirePoint = Tool.GlockMesh.BulletPoint
local BulletCoroutine
local RBullet

local Params = RaycastParams.new()
Params.FilterDescendantsInstances = {}
Params.FilterType = Enum.RaycastFilterType.Blacklist

-- Tool Data --
local IsAutomatic = true
local LastShotTime = os.clock()
local FireRate = 0.1

local MagAmmo = Tool.Data.MagAmmoNum
local IsHeldDown = false
local Distance = 500
local Bullet = game.ReplicatedStorage.Bullets.NormalBullet
--           --

-- Functions --
local function FireClientBullet(MPos)
	local DebugPart1 = workspace.DebugPart1
	local DebugPart2 = workspace.DebugPart2
	
	-- The Part i dont understand well --
	local Rv = MPos.Direction * 300
	local Ray1 = workspace:Raycast(MPos.Origin, (Rv * Distance), Params)
	
	local HitPos = if Ray1 then Ray1.Position else (MPos.Origin + Rv)
	local AimAt = (HitPos - FirePoint.WorldPosition)
	
	local BulletRay = workspace:Raycast(FirePoint.WorldPosition, AimAt * 2, Params)
	local ThingHit = if BulletRay then BulletRay.Instance else nil
	local PosHit = if BulletRay then BulletRay.Position else HitPos
	--                                 --
	
	local BClone = Bullet:Clone()
	BClone.Size = Vector3.new(.2, .2, (FirePoint.WorldPosition - HitPos).Magnitude)
	BClone.CFrame = CFrame.new(FirePoint.WorldPosition:Lerp(HitPos, .5), HitPos)
	BClone.Parent = workspace
	
	Ts:Create(BClone, TweenInfo.new(.3, Enum.EasingStyle.Quad), {Transparency = 1}):Play()
	Debris:AddItem(BClone, .4)
end

local function Shoot()
	local Mouse = UserInputService:GetMouseLocation()
	local MousePosition = workspace.CurrentCamera:ViewportPointToRay(Mouse.X, Mouse.Y)
	local DirectTime = os.clock()

	CTS:FireServer("Fire")
	FireClientBullet(MousePosition)
end


-- Main
Tool.Activated:Connect(Shoot)

[azqjanna]

Do a first raycast in the mouse direction up to 300 units away. If the ray hits something store its hit position, otherwise store the point at the maximum distance (300) in the mouse direction. Calculate the direction from the FirePoint (looks like its an attachment on your weapon) to this HitPos.
Cast a second ray in this direction with up to twice the previous max length. If this rays hits anything store the instance in ThingHit and the position in PosHit.

[123jar456on2]

If your confused about the if statements in variables, its basically checking a condition, if its true, then it will assign the variable to one thing, if its false, it assigns it to another.
For example, the line

local ThingHit = if BulletRay then BulletRay.Instance else nil

It will create the variable “ThingHit”. If “BulletRay” exists, then it will be assigned BulletRay.Instance. If “BulletRay” does not exist, or is nil, then it will assing “ThingHit” to nil.

[BobbieTrooper (Jesse)]

-- Fix:

local function FireClientBullet(MPos)
	local DebugPart1 = workspace.DebugPart1
	local DebugPart2 = workspace.DebugPart2
	
	-- The Part i dont understand well --
	local Rv = MPos.Direction * 300
	local Ray1 = workspace:Raycast(MPos.Origin, (Rv * Distance), Params)
	
	local HitPos = Ray1 and Ray1.Position or (MPos.Origin + Rv)
	local AimAt = (HitPos - FirePoint.WorldPosition)
	
	local BulletRay = workspace:Raycast(FirePoint.WorldPosition, AimAt * 2, Params)
	local ThingHit = BulletRay and BulletRay.Instance or nil
	local PosHit = BulletRay and BulletRay.Position or HitPos
	--                                 --
	
	local BClone = Bullet:Clone()
	BClone.Size = Vector3.new(.2, .2, (FirePoint.WorldPosition - HitPos).Magnitude)
	BClone.CFrame = CFrame.new(FirePoint.WorldPosition:Lerp(HitPos, .5), HitPos)
	BClone.Parent = workspace
	
	Ts:Create(BClone, TweenInfo.new(.3, Enum.EasingStyle.Quad), {Transparency = 1}):Play()
	Debris:AddItem(BClone, .4)
end

local function Shoot()
	local Mouse = UserInputService:GetMouseLocation()
	local MousePosition = workspace.CurrentCamera:ViewportPointToRay(Mouse.X, Mouse.Y)
	local DirectTime = os.clock()

	CTS:FireServer("Fire")
	FireClientBullet(MousePosition)
end


-- Main
Tool.Activated:Connect(Shoot)

The code uses Raycast functions to find the location of the point the mouse is pointing at when the tool is activated. It uses the Raycast to calculate the distance between the FirePoint and the HitPos, and then uses this to fire a bullet at the HitPos. It also sets the size of the bullet based on the distance between the FirePoint and the HitPos.

[simplyjustbased]

Sorry for the long response, forgot this post existed until now

@azqjanna

. Calculate the direction from the FirePoint (looks like its an attachment on your weapon) to this HitPos.

I think this goes over it but how does

@simplyjustbased

local AimAt = (HitPos - FirePoint.WorldPosition)

This work in here

@simplyjustbased

local BulletRay = workspace:Raycast(FirePoint.WorldPosition, AimAt * 2, Params)

i move a debugpart to the AimAt position and its at some completely other position but the ray still ends up being accurate

[7z99 (cody)]

@simplyjustbased

I think this goes over it but how does

@simplyjustbased

local AimAt = (HitPos - FirePoint.WorldPosition)

This work in here

@simplyjustbased

@simplyjustbased

local BulletRay = workspace:Raycast(FirePoint.WorldPosition, AimAt * 2, Params)

i move a debugpart to the AimAt position and its at some completely other position but the ray still ends up being accurate

In essence the formula in the first quote calculates the direction between two points (direction = goal - origin)

Subtracting the goal from the origin gives you a vector, this vector represents ‘goal’'s position relative to ‘origin’, which is also the direction.

So suppose you’re given this: two points (vectors) and you need to find the direction of “goal” relative to “origin”

Let’s suppose “goal” is at (14, 9) and “origin” is at (6, 5)

To get the direction we subtract “origin” from “goal” which gives us another vector which is the vector where if we suppose “origin” is (0, 0), provides ‘goal’'s position (which is the same as saying ‘goal’ relative to ‘origin’)

Because you’re performing this subtraction, it makes sense that putting a debug part at this position seems to give a random position. To get the right position, you’d have to do part.Position = FirePoint.WorldPosition + AimAt * 2.

Also although not directly related, if you want a better understanding of how to visualize a ray and how vectors have lengths, you can look at this post I made awhile ago:

How to Visualize specific pieces of code, and understand them

It’s hard to visualize but I’ll try my best: I’ll be first demonstrating question 1 and 3 because they kinda go together: First thing, .Unit returns the same vector except it’s limited to 1 stud from the “origin”, and 1 stud is what what “Unit” refers to. It’s usually useful for when we want to easily specify a certain distance to cast a ray from: print(Vector3.new(1000,1000,1000).Unit) --> 0.57735025882721, 0.57735025882721, 0.57735025882721 To visualize, let’s say I have this part, the pin…

[simplyjustbased]

Damn, gonna take me a of re-reading to understand this but it looks like it covers what im asking

i just got one more question,
for this

@simplyjustbased

local BulletRay = workspace:Raycast(FirePoint.WorldPosition, AimAt * 2, Params)

Why do i have to multiply the AimAt*2?, i dont really know whats going on but if i dont multiply it the endpoint is off

[7z99 (cody)]

At first glance I don’t think you shouldn’t have to multiply it by 2.

Only thing I can think of is that your ray is just a tiny bit shorter than what is needed to hit the part due to floating point limitations or something of that nature. You could probably try multiplying it by something like 1.05 and see if that does anything, but vector math is very fast in Luau, especially now that vectors are a native type, so I wouldn’t worry about it too much if you’re concerned about performance.

Is there a reason you need 2 rays for this though? Looking at your code I’m thinking using the first ray alone would suffice.

[simplyjustbased]

@7z99

At first glance I don’t think you shouldn’t have to multiply it by 2.

i did try to rename parts of the to code make it more readable, could just be me messing something up (just checked it by removing the *2, it was on my part of messing something up)

@7z99

Is there a reason you need 2 rays for this though? Looking at your code I’m thinking using the first ray alone would suffice.

not even sure, this is some old code im just reusing that i got from some other place a long time ago

but using debug parts on the first and second ray, the parts dont always line up. So somethings changing
Heres the “rewritten” code if i did mess something up

repeat task.wait() until game:IsLoaded() and script.Parent:FindFirstChild("Remotes")

-- Variables
local Player = game:GetService('Players').LocalPlayer
local UserInputService = game:GetService("UserInputService")
local RunService = game:GetService("RunService")
local Ts = game:GetService("TweenService")
local Debris = game:GetService("Debris")

local Tool = script.Parent
local RemotesFolder = Tool.Remotes
local RSRemotesFolder = game.ReplicatedStorage.Remotes
local Mesh = Tool.GlockMesh
local Handle = Tool.Handle
local BulletPoint = Mesh.BulletPoint
local ClientBullet = RSRemotesFolder.ClientBullet
local BulletFolder = game.ReplicatedStorage.Bullets
local FirePoint = Tool.GlockMesh.BulletPoint
local ShootEvent = RemotesFolder.Shoot
local ReloadEvent = RemotesFolder.Reload
local CheckEvent = RemotesFolder.Check
local BulletCoroutine
local RBullet

local Params = RaycastParams.new()
Params.FilterDescendantsInstances = {}
Params.FilterType = Enum.RaycastFilterType.Blacklist

-- Tool Data --
local IsAutomatic = true
local LastShotTime = os.clock()
local FireRate = 0.1

local IsHeldDown = false
local Distance = 500
local Bullet = game.ReplicatedStorage.Bullets.NormalBullet
--           --

-- Functions --
local function FireClientBullet(MousePosition)
	local Dbp1 = workspace.DebugPart1
	local Dbp2 = workspace.DebugPart2
	
	local MouseDirection = MousePosition.Direction * Distance
	local MouseRay = workspace:Raycast(MousePosition.Origin, MouseDirection, Params)
	
	local MouseRayPosition = if MouseRay then MouseRay.Position else (MousePosition.Origin + MouseDirection)
	Dbp1.Position = MouseRayPosition

	local BulletDirection = (MouseRayPosition - FirePoint.WorldPosition)
	
	local BulletRay = workspace:Raycast(FirePoint.WorldPosition, BulletDirection, Params)
	local HitPart = if BulletRay then BulletRay.Instance else nil
	local HitPosition = if BulletRay then BulletRay.Position else MouseRayPosition       
	Dbp2.Position = HitPosition
	
	local BClone = Bullet:Clone()
	BClone.Size = Vector3.new(.2, .2, (FirePoint.WorldPosition - HitPosition).Magnitude)
	BClone.CFrame = CFrame.new(FirePoint.WorldPosition:Lerp(HitPosition, .5), HitPosition)
	BClone.Parent = workspace
	
	Ts:Create(BClone, TweenInfo.new(.3, Enum.EasingStyle.Quad), {Transparency = 1}):Play()
	Debris:AddItem(BClone, .4)
end

local function Shoot()
	local Mouse = UserInputService:GetMouseLocation()
	local MousePosition = workspace.CurrentCamera:ViewportPointToRay(Mouse.X, Mouse.Y)
	local DirectTime = os.clock()

	ShootEvent:FireServer(MousePosition)
	FireClientBullet(MousePosition)
end

local function OnEquip()
	local Character = Tool.Parent
	
	Params.FilterDescendantsInstances = {Character}
end

local function OnUnequip()
	Params.FilterDescendantsInstances = {}
end


-- Main
Tool.Activated:Connect(Shoot)
Tool.Equipped:Connect(OnEquip)
Tool.Unequipped:Connect(OnUnequip)

(edit)
yeah i got something wrong at somepoint, it shows a hit on the client, but its off on server
for the server script i hastily remade the client script and made it to work on server
i dont know what i did wrong this time, could be the script or the bullet creation im lost in this messy script

Scripts

Client’s Version of the shooting

local function FireClientBullet(MousePosition)
	local Dbp1 = workspace.DebugPart1
	local Dbp2 = workspace.DebugPart2
	
	local MouseDirection = MousePosition.Direction * Distance
	local MouseRay = workspace:Raycast(MousePosition.Origin, MouseDirection, Params)
	
	local MouseRayPosition = if MouseRay then MouseRay.Position else (MousePosition.Origin + MouseDirection)
	Dbp1.Position = MouseRayPosition

	local BulletDirection = (MouseRayPosition - FirePoint.WorldPosition)
	
	local BulletRay = workspace:Raycast(FirePoint.WorldPosition, BulletDirection, Params)
	local HitPart = if BulletRay then BulletRay.Instance else nil
	local HitPosition = if BulletRay then BulletRay.Position else MouseRayPosition       
	Dbp2.Position = HitPosition
	
	local BClone = Bullet:Clone()
	BClone.Size = Vector3.new(.2, .2, (FirePoint.WorldPosition - HitPosition).Magnitude)
	BClone.CFrame = CFrame.new(FirePoint.WorldPosition:Lerp(HitPosition, .5), HitPosition)
	BClone.Parent = workspace
	
	Ts:Create(BClone, TweenInfo.new(.3, Enum.EasingStyle.Quad), {Transparency = 1}):Play()
	Debris:AddItem(BClone, .4)
end

Servers version of the shooting

local function OnShoot(Player, MousePos)
	if Tool.Parent.Name:lower() == "backpack" then return end
	local FirePointPosition = FirePoint.WorldPosition
	local MouseRay = workspace:Raycast(MousePos.Origin, (MousePos.Direction * Distance), RCP) 
	
	local MouseRayPosition = if MouseRay then MouseRay.Position else (MousePos.Origin + (MousePos.Direction * Distance))
	local BulletDirection = MouseRayPosition - FirePointPosition
	
	local BulletRay = workspace:Raycast(FirePointPosition, BulletDirection, RCP)
	
	local BulletHit = if BulletRay then BulletRay.Instance else nil
	local BulletPosition = if BulletRay then BulletRay.Position else MouseRayPosition
	
	if BulletHit and BulletHit.Parent and BulletHit.Parent:FindFirstChild("HumanoidRootPart") then
		HitPlayer(BulletHit.Parent)
	end
end