How to tell if a part touched a player's back

[42Spider_man42 (nubdudub)]

I would like to tell which face a part touches of a character’s torso and, if that face is the back.
I don’t know how to word this better sorry.

I found this script which I thought might help but I don’t really understand it:

function getSurface(position, object)
	local surfaces = {
		back = object.CFrame * CFrame.new(0, 0, object.Size.Z);
		front = object.CFrame * CFrame.new(0, 0, -object.Size.Z);
		top = object.CFrame * CFrame.new(0, object.Size.Y, 0);
		bottom = object.CFrame * CFrame.new(0, -object.Size.Y, 0);
		right = object.CFrame * CFrame.new(object.Size.X, 0, 0);
		left = object.CFrame * CFrame.new(-object.Size.X, 0, 0);
	}
	local surface = "back"
	for side, cframe in pairs (surfaces) do
		surface = ((position - cframe.p).magnitude > (position - surfaces[surface].p).magnitude and surface or side)
	end
	return surface
end

thanks

[bluebxrrybot (blueberry)]

You cannot determine exactly where the touch happens, you’ll have to make a small hitbox on the player’s back instead.

[42Spider_man42 (nubdudub)]

like welding a part to a player’s back when they join or something?

[bluebxrrybot (blueberry)]

Yes, it would be welded to the player’s HumanoidRootPart. An uncollidable, massless, and unanchored part. Also, set the CustomPhysicalProperties to set the Density to 0.

[AlreadyPro (Logan)]

You can use this function to get the angle between a CFrame and a Position

local function getAngleBetween(origin: CFrame, target: Vector3): number
	local lookVector: Vector3 = origin.LookVector
	local unit: Vector3 = (target - origin.Position).Unit

	return math.deg(math.acos(unit:Dot(lookVector)))
end

To determine if a Part is behind a player,

local angle = getAngleBetween(character:GetPivot(), part.Position)

if angle >= 135 then
    print("Part is behind the Player's Character")
end

[42Spider_man42 (nubdudub)]

so there is a slight problem, you can hit the part through the player’s torso:

I’m not sure if I should make this another topic or not

also thanks for your help!