How to translate the accelerometer input by specific angle?

Question

I have an orthographic camera set on position(0,0,-10), rotation(0,0,0) and it's parent - CameraHolder with a transform:

which gives an isometric feel:

Now, I need to move the ball with the accelerometer so here's how the FixedUpdate() looks like:

   void FixedUpdate ()
     {
         if (SystemInfo.deviceType == DeviceType.Desktop) 
         { 
             // Player movement in desktop devices
             // Definition of force vector X and Y components
             float moveHorizontal = Input.GetAxis("Horizontal");
             float moveVertical = Input.GetAxis("Vertical");


             // Building of force vector
             Vector3 movement = new Vector3 (moveHorizontal,0.0f,moveVertical);
             // Adding force to rigidbody
             rigidbody.AddForce(movement * speed * Time.deltaTime);
         }
         else
         {
             // Player movement in mobile devices
             // Building of force vector 
             Vector3 movement = new Vector3 (Input.acceleration.x, 0.0f, Input.acceleration.y);
             // Adding force to rigidbody
             rigidbody.AddForce(movement * speed * Time.deltaTime);
         }
     }

The movement looks like this:

And I want it to move like:

I need to translate the movement by 45 degrees, but I have no idea how.

If anyone has a clue, I'd be grateful for help!

Answer 1

If the movement will always be camera locked, you can compute the movement vectors using the camera transform.

You would use this whenever the camera rotates

//Take care to normalize AFTER setting y to 0
Vector3 camFwd = cam.transform.forward;
camFwd.y = 0; camFwd = camFwd.normalized;

Vector3 camRight = cam.transform.right;
camRight.y = 0; camRight = camRight.normalized;

and you would use this whenever movement should occur

Vector3 acc = Input.acceleration;
Vector3 movmenet = new Vector3(camRight * acc.x,0.0f,camFwd * acc.z);

You could also use a Quaternion / Matrix and rotate the vector, but that's way more costly and complicated than necessary.