How to calculate the dot product between the input direction and a character with root motion?

Question

I need to calculate the dot product between my character movement direction and the input being pressed by the player. When the character movement was being controlled only by code, I was using something like this:

movementInputVector = new Vector3(inputDirection.y, 0, inputDirection.x) * Time.fixedDeltaTime;
rigidbody.MovePosition(transform.position + movementInputVector);

With this movement code, it was possible to calculate the dot product using the character's tansform.forward and the movement input vector.

It happens that I discovered that my movement needs to use root motion and after this change, I can't find a way to generate a consistent dot product anymore. Already did some attempts, but none of them worked.

Firstly, I tried to use the transform.forward, as it did worked before:

MovementDirectionDot = Vector3.Dot(transform.forward, movementInputVector);

But the result was 0, no matter the direction I pressed as input.

Then I tried to use the root bone of the character as reference:

MovementDirectionDot = Vector3.Dot(rootBoneTransform.forward, movementVector);

This attempt generated inconsistent values from ~-0,07 to ~9.

Taking a look at the transform.forward values, I've noticed it doesn't change as the character moves, remaining as a vector3(0,0,1) the whole time. Also, I tried to normalize all vectors involved and the same results happened.

So I have no clue what to do now, I don't know what vector should be used in this method in order to get back the correct dot product ranging from -1 to 1. Does anyone have an insight on this?

Answer 1

So after revise everything again and again I stopped to take a closer look on two vectors I was using to generate the dot. It happens that the "movementVector" is a vector2 and the "transford.forward" is a vector3, as the movement in a 3D ground happens in the X and Z axis, the results never would be right. So my solution was to create a vector3 using the movementVector as base, inverting the value on X axis(for some reason the original value is opposed of the transform.forward one), so I solved the problem using this 2 lines:

var convertedMovementVector = new Vector3(movementVector.y, 0, -movementVector.x);
    MovementDirectionDot = Vector3.Dot(convertedMovementVector, transform.forward);

The results are consistent now, so I believe this is a good solution for my case, even looking like an improvisation.