Trying to find the closest part

[WillyDevz (Willy)]

Hello, I am trying to make an auto lock-on grappler where it automatically locks on to the closest part to the players mouse. So for an example in this image, my mouse is closer to part 2 than part 1, so it should lock to part 2 instead of part 1. how would I achieve this?

[yoshicoolTV (coolyoshi)]

You could try using a mouse raycast and setting something up with this code snippet i found in the forums

How to find nearest part to player

Something like this would work: local ClosestMagnitude = math.huge() local ClosestPart = nil for _, Part in pairs(workspace.Parts:GetChildren()) do if (Part.Position - <player>.Position).Magnitude < ClosestMagnitude then ClosestMagnitude = (Part.Position - <player>.Position).Magnitude ClosestPart = Part end end

[NexnHeimer (NexoBeats)]

you should use UserInputService and MouseRaycast for that.

workspace:Raycast()
-- for example

[VegetationBush (FartedWayTooHard)]

Using raycasting for this type of problem will not work. It’s unrelated to what you’re trying to achieve.

---

Luckily, Roblox gives us API to solve this problem. This API is called WorldToScreenPoint, which is a method of the Camera class. This method takes a 3D point in the world and tells you where that point is on the screen (basically, it transforms a 3D point to a 2D point).

Knowing this, we can get the 3D positions of the two parts:

local part1WorldPos = Part1.Position
local part2WorldPos = Part2.Position

Then, you can use WorldToScreenPoint to determine where the point lies on the screen:

local Camera = workspace.CurrentCamera

local part1ScreenPos = Camera:WorldToScreenPoint(part1WorldPos)
local part2ScreenPos = Camera:WorldToScreenPoint(part2WorldPos)

Now, you can get the distance of the screen positions with the mouse position:

local mousePos = UserInputService:GetMouseLocation()

-->> .Magnitude gets the length of the vector
-->> converting to Vector2 as GetMouseLocation returns a Vector3
local part1Distance = (mousePos - Vector2.new(part1ScreenPos.X, part1ScreenPos.Y)).Magnitude
local part2Distance = (mousePos - Vector2.new(part2ScreenPos.X, part2ScreenPos.Y)).Magnitude

Lastly, you can compare the distances. The smallest distance is the closest part:

if part1Distance < part2Distance then
    print("Part1 is closer to the mouse!")
else
    print("Part2 is closer to the mouse!")
end

Full code

local Camera = workspace.CurrentCamera
local mousePos = UserInputService:GetMouseLocation()

-->> world positions
local part1WorldPos = Part1.Position
local part2WorldPos = Part2.Position

-->> screen positions
local part1ScreenPos = Camera:WorldToScreenPoint(part1WorldPos)
local part2ScreenPos = Camera:WorldToScreenPoint(part2WorldPos)

-->> distance from mouse
local part1Distance = (mousePos - Vector2.new(part1ScreenPos.X, part1ScreenPos.Y)).Magnitude
local part2Distance = (mousePos - Vector2.new(part2ScreenPos.X, part2ScreenPos.Y)).Magnitude

if part1Distance < part2Distance then
    print("Part1 is closer to the mouse!")
else
    print("Part2 is closer to the mouse!")
end

[WillyDevz (Willy)]

Thank you! This was the solution, the only problem I had was that I got an error, and that’s because the part1ScreenPos was a vector3, so the only thing that needed to be changed was

local part1Distance = (mousePos - part1ScreenPos).Magnitude
local part2Distance = (mousePos - part2ScreenPos).Magnitude

to

local part1Distance = (mousePos - Vector2.new(part1ScreenPos.X, part1ScreenPos.Y)).Magnitude
local part2Distance = (mousePos - Vector2.new(part2ScreenPos.X, part2ScreenPos.Y)).Magnitude

Thank you again!