How to Rotate a Vector

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#1

There’s a fly script I’m working on where an AlignOrientation orients a character’s HumanoidRootPart based on their camera LookVector.

local camlookat = camcframe.LookVector
alignOrientation.CFrame = CFrame.new(rootpart.CFrame.Position, rootpart.CFrame.Position + camlookat)

It works, but the problem is that it makes the front of the HumanoidRootPart face the LookVector of the Camera, while I want the top of the HumanoidRootPart to face the camera LookVector whilst the front faces the negative UpVector of the Camera.

Basically I want the player to fly head-first, face-down.

I tried rotating the LookVector on an axis using the function in this post, but the results are really wonky

How may I achieve what I’m looking for?

#2

You could just plus it with a cframe.angles, heres an example:

local camlookat = camcframe.LookVector
alignOrientation.CFrame = CFrame.new(rootpart.CFrame.Position, rootpart.CFrame.Position + camlookat) * CFrame.Angles(math.rad(-90),0,0)

With this, the alignorientation will look to the camera look vector, but with the top of the humanoidrootpart being rotated to the front, as you want.

Hope it helps!

#3

If this is the case, this is pretty much the answer to your question, we can just create a new rotation matrix using these vectors.

Does this give you what you’re looking for?

local up = camera.CFrame.LookVector
local negLook = camera.CFrame.UpVector
local right = up:Cross(negLook)

alignOrientation.CFrame = CFrame.fromMatrix(
	root.Position,
	right,
	up,
	negLook -- the z vector is flipped in Roblox so the look vector is negative Z axis
)
1 Like
#4

I tried this already but for some reason it flips when looking downwards

#5

Nice! This almost worked, but not quite.

Here’s the behavior:

Basically, when looking anywhere up-ish, it works as intended. When looking anywhere down-ish, it does the opposite of what intended…

Any ideas as to what causes this?

#6

Oh that’s interesting, could you provide your script or a repro file? It’s working as expected for me

Medal_KJy5wSPm1h

Or here’s what my implementation looked like if you want to gloss over it:

local camera = workspace.CurrentCamera

local root = script.Parent:WaitForChild('HumanoidRootPart')
local attachment = Instance.new('Attachment', root)

local alignOrientation = Instance.new('AlignOrientation')
alignOrientation.Mode = Enum.OrientationAlignmentMode.OneAttachment
alignOrientation.RigidityEnabled = true
alignOrientation.Attachment0 = attachment
alignOrientation.Parent = root

local alignPosition = Instance.new('AlignPosition')
alignPosition.Mode = Enum.PositionAlignmentMode.OneAttachment
alignPosition.RigidityEnabled = true
alignPosition.Attachment0 = attachment
alignPosition.Position = root.Position + Vector3.yAxis * 3
alignPosition.Parent = root

game:GetService('RunService').RenderStepped:Connect(function()
	local up = camera.CFrame.LookVector
	local negLook = camera.CFrame.UpVector
	local right = up:Cross(negLook)

	alignOrientation.CFrame = CFrame.fromMatrix(
		root.Position,
		right,
		up,
		negLook -- the z vector is flipped in Roblox so the look vector is negative Z axis
	)
end)
2 Likes
#7

Gosh thanks!

Indeed the problem was on my end there, I was applying the CFrame incorrectly, like this

alignOrientation.CFrame = CFrame.new(rootpart.CFrame.Position, rootpart.CFrame.Position + (camfixedcframe.LookVector))

Now that I’ve done it as you did

alignOrientation.CFrame = camcframe

It works. Thanks again!

1 Like
#8

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