Limit a ray to not go beyond a plane - roblox

Question

As you can see from the image
I want the mouse hit to not go beyond the origin’s position. If anyone knows about this, I’d like to know.
My first idea was subtract the origin to mouse hit's position and get their magnitude then subtract the mouse hit with mouse hit's look vector(unit vector) multiplied by the magnitude, but this does not work.

Answer 1

From your image, it's a little unclear what defines the plane that is your limit? I'm going to assume that it is the plane defined by the face of a box, and the normal vector to that face.
You know the camera position, and the direction of your ray, so once you define your plane, you should be able to calculate the intersection of that plane with your ray.
See Ray-plane intersection by Scratchapixel. They have done an excellent job breaking down the equations that make this work. (Note, for this code I have renamed the l variables to r, as the variable l0 was somewhat easy to mistake for the constant 10)
In a LocalScript, try this...
local WorldWorkspace = game:GetService("Workspace")
local Players = game:GetService("Players")
local part = WorldWorkspace.Part
local camera = WorldWorkspace.CurrentCamera
local player = Players.LocalPlayer
local mouse = player:GetMouse()
--[[
GIVEN THE EQUATIONS...
(p - p0) ⋅ n = 0
where...
- p is the intersection point (Vector3)
- p0 is the origin of the plane (Vector3)
- n is the plane perpendicular to the origin point (Vector3)
(r0 + r * t) = p
where...
- r0 is the origin of the ray (Vector3)
- r is the ray direction (Vector3, normalized)
- t is the length of the ray (Vector3)
- p is the intersection point (Vector3)
THEREFORE...
r * t ⋅ n + (r0 - p0) ⋅ n = 0
AND SOLVING FOR t WE GET...
t = ((p0 - r0) ⋅ n) / (r ⋅ n))
]]
local function calculateIntersection(n : Vector3, p0 : Vector3, r : Vector3, r0 : Vector3) : (boolean, Vector3?)
-- returns false if the ray defined by r0 and r will never intersect with the plane defined by p0 and n
local denominator : Vector3 = n:Dot(r)
if denominator > 0 then
local p010 : Vector3 = p0 - r0
local t : Vector3 = p010:Dot(n) / denominator
local doesIntersect : boolean = t >= 0
local p : Vector3? = if doesIntersect then (r0 + (r * t)) else nil
return doesIntersect, p
end
return false, nil
end
local function getOrigin() : Vector3
-- calculate the origin of the intersection plane by simply using the rough bounding box.
local cubeCenter = part.CFrame.Position
local cubeSize = part.Size
-- return the back face of the cube for testing
return cubeCenter + Vector3.new(0, 0, cubeSize.Z * 0.5)
end
local function getPlane() : Vector3
local right = part.CFrame.RightVector
local up = part.CFrame.UpVector
local normalPlane = right:Cross(up).Unit
-- multiply by -1 to invert the outward direction of plane
return -1 * normalPlane
end
local function onClick()
-- NOTE - tweak the values of p0 and n to get the plane right
local p0 = getOrigin()
local n = getPlane()
local r = mouse.Origin.LookVector
local r0 = mouse.Origin.Position
local success, result = calculateIntersection(n, p0, r, r0)
if success then
-- draw a ball where the point intersects with the plane
-- NOTE - this will only draw on the local client, not the server
local ball = Instance.new("Part")
ball.Shape = Enum.PartType.Ball
ball.Size = Vector3.new(0.2, 0.2, 0.2)
ball.Position = result
ball.Anchored = true
ball.CanCollide = false
ball.Color = Color3.new(1, 0, 0)
ball.Parent = WorldWorkspace
end
end
-- listen for when the player clicks
mouse.Button1Down:Connect(onClick)
In my testing, I was able to lock collisions to the defined plane, but I needed to mess around with the getOrigin and getPlane functions to properly define where I wanted the plane to be.