Edge Detection from Mouse

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#6

The ray doesnt know if the edge is hit, it only returns what it hit and the position and the surface normal

#8

So if the ray hits the position of the edge then u could do whatever u want…

The ray will stay active until it hits the edge of the position u want it to hit

#9

Yeah but I would have to have a part at every edge, which is not the way I want to do it…

#10

No, put a part at the edge and measure the position then delete it, in ur script say if the ray hits the position the part was at then so on…

#11

Thats still very inefficient because if I have parts that are not the same size illl have to do that for every single part, also I doubt that would work properly

1 Like
#12

Duplicate the parts?, just scale it to your needs then if the ray hits the position the part was at then so on…

#13

I dont think your understanding what Im trying to achieve, basically I want to get the edge of a part from my mouse position without the need of making parts

#14

@ThoseNamesAreGood Raycasting will help, but not without the use of the surface normal. You can use the surface normal returned to determine the corner.

#15

Hm, could you explain further please

#16

The normal is a vector perpendicular to the tangential surface returned during a raycast operation. For example, (0, 1, 0) is an up vector, (0, -1, 0) is a down vector. You can use the returned normal to get an angle.

#17

Alright but after that what do I do with that angle?

#18

You want to detect the edge, so you can use the angle to determine if the surface is an edge.

#19

Could you give an example of this at least your kinda of just throwing stuff at me

#20

I do not think you can use a normal of or deduce the angle to help figure out if you hit an edge. An edge isn’t part of a face anyways, it defines a face, so it’d be impossible to actually “hit” the edge literally. You’d need to give a range from 0 to X (like 0.01) studs away from the edge to define as the edge.

#21

Basically, if you’re trying to figure out which edge of a part a Vector3 is closest to, I would do something like this:

  1. Get the position in object space - use local localPos = Part.CFrame:ToObjectSpace(mousePosition).p for that
  2. Check the components of that vector.
  3. (for example) If localPos.X is close to Part.Size.X / 2, then you’re on the right-side face. If localPos.Y is also close to -Part.Y / 2, then you’re also on the bottom-side face. Hurray! Now you know you’re on the right-bottom edge!
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#22

This would work just fine. This way, you can set a tolerance of what is accepted as the edge and what is not.

#23

Untested, but I got bored so this should do it:

-- Given a part and a position, returns which faces the position lies on or is
-- within `epsilon` studs of.
-- @returns a Faces object: https://developer.roblox.com/en-us/api-reference/datatype/Faces
local function WhichFaces(part, position, epsilon)
    epsilon = epsilon or 0.1
    
    local pos = part.CFrame:ToObjectSpace(position)
    
    local halfSize = part.Size / 2
    
    -- first check that we're within the part's outside bounds
    if math.abs(pos.Y) < halfSize.Y + epsilon
        and math.abs(pos.Z) < halfSize.Z + epsilon
        and math.abs(pos.X) < halfSize.X + epsilon
        then
        
        local faces = {}
        
        -- check if we're close to an edge
        if pos.Y > halfSize.Y - epsilon then table.insert(faces, Enum.NormalId.Top) end
        if pos.Y < epsilon - halfSize.Y then table.insert(faces, Enum.NormalId.Bottom) end
        
        if pos.Z > halfSize.Z - epsilon then table.insert(faces, Enum.NormalId.Back) end
        if pos.Z < epsilon - halfSize.Z then table.insert(faces, Enum.NormalId.Front) end
        
        if pos.X > halfSize.X - epsilon then table.insert(faces, Enum.NormalId.Right) end
        if pos.X < epsilon - halfSize.X then table.insert(faces, Enum.NormalId.Left) end
        
        return Faces.new(unpack(faces))
    else
        return Faces.new()
    end
    
end

-- USAGE e.g.

local mousePosition = Vector3.new(1, 1, 0)
local myPart = workspace.Part

local faces = WhichFaces(myPart, mousePosition)

if faces.Top then
    print("Top face!")
    
    if faces.Front then
        print("Top-front edge too!")
        
        if faces.Right then
            print("Top-front-right corner!")
        end
        
    elseif faces.Left then
        print("Top-left edge!")
    end
    -- etc.
end
6 Likes
I'm struggling with CFrame!
#24

But this is assuming that all parts are rectangular, doesn’t account for unions nor mesh parts, nor wedges, nor spheres, nor cylinders, right?

#25

I have an idea
how about do

local a1 = part.Size + (Part.Position/2)
local a1 = part.Size - (Part.Position/2)

Or something like that
using region three I think it’s possible!

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#26

How can i get this to work correctly…