Setting neck C0 will move the torso and HumanoidRootPart instead of the Head

[PostVivic (Vivic)]

Hi devforum, I am having an issue trying to make a fps camera similar to the one in Beaks. I got the “shift lock” implementation down thanks to this amazing article

How to Force Enable Shift-Lock (Without changing the PlayerModule)

Introduction Hello developers ! I have seen many games accomplish some kind of “Force shift locking”, and most threads I’ve seen change the PlayerModule. This method accomplishes about the same result without changing the PlayerModule by CFraming. I believe this method is simpler, and if the PlayerModule changes again, this will still work. End Result: This Method Utilizies: UserInputService.MouseBehavior Humanoid.CameraOffset RunService.RenderStepped / RunService.…

However when adding my own code to change the Neck joint to look in the direction im facing, I encountered a weird issue where the Root part will rotate instead of the head itself

RS.RenderStepped:Connect(function()
	local Character = game.Players.LocalPlayer.Character
	if not Character then return end
	local Humanoid = Character:FindFirstChildOfClass("Humanoid")
	local HRP = Character.PrimaryPart
	local Head = Character:FindFirstChild("Head")
	local Torso = Character:FindFirstChild("Torso")
	if not Humanoid or not HRP or not Head or not Torso then return end
	local RS = game:GetService("RunService")
	
	local target = workspace.CurrentCamera.CFrame.Rotation:ToEulerAnglesYXZ()
	
	target = target * TorsoLock.EnabledAlpha.Value
	
	local NeckJoint = Torso:FindFirstChild("Neck")
	if NeckJoint then
		local nx, ny, nz = NeckJoint.C0:ToEulerAnglesXYZ()

		NeckJoint.C0 = CFrame.new(NeckJoint.C0.Position) * CFrame.Angles(target - math.rad(90), ny, nz)
	end		
end)

This is the code that is responsible for rotating the neck

and this is the result

I narrowed down the bug down to my ShiftLock controller

RS:BindToRenderStep("ShiftLock", Enum.RenderPriority.Camera.Value - 1, function()
	local Character = game.Players.LocalPlayer.Character
	if not Character then return end
	local Humanoid = Character:FindFirstChildOfClass("Humanoid")
	local HRP = Character.PrimaryPart
	local Head = Character:FindFirstChild("Head")
	if not Humanoid or not HRP or not Head then return end
		
	local isZoomedIn = ((Head.Position + HRP.CFrame.Rotation:VectorToWorldSpace(Humanoid.CameraOffset)) - workspace.CurrentCamera.CFrame.Position).Magnitude < 1
		
	if isZoomedIn then
		Humanoid.CameraOffset = Vector3.zero
		Humanoid.AutoRotate = true
		return
	end
		
	Humanoid.CameraOffset = CAMERA_OFFSET * PsuedoShiftLock.EnabledAlpha.Value
		
	if PsuedoShiftLock.EnabledAlpha.Value ~= 0 then
		Humanoid.AutoRotate = true
		local x, y, z = workspace.CurrentCamera.CFrame.Rotation:ToEulerAnglesYXZ()
		--commenting out the line below fixes the issue
		HRP.CFrame = CFrame.new(HRP.Position) * CFrame.Angles(0, y, 0)
	else
		
		Humanoid.AutoRotate = true
	end
end)

I have tried all different combinations of render orders, where the shift lock runs before and after the look order, messed around with render functions before and after physics simulation

I have also tried using PivotTo() instead of the CFrame.new() shown

[PostVivic (Vivic)]

Apologies I stumbled upon my answer, Apparently for R6 rigs, the PrimaryPart is the Head instead of the HumanoidRootPart.

This meant instead of moving the HumanoidRootPart like I intended, I was actually moving the head.