koobas.hobune.stream
Slerp FPS gun rotation in VR
I'm trying to add a slight gun sway effect to a FPS gun in VR.
All works fine if I make the Gun a child of the VR camera but the rotation (aiming) of the gun is too exact - it follows the VR head movement too closely.
I'd like to move the Gun out of the GvrMain game object and use a script to make it follow the position and rotation of the VR head but with a slight delay (slerp).
I've done this successfully in another game with a spaceship cockpit, by adding this script to the cockpit:
public class HudFloat : MonoBehaviour {
private Transform mainCam;
public float smoothTime = 0.15F;
void Start () {
mainCam = Camera.main.gameObject.transform;
}
void FixedUpdate() {
transform.rotation = Quaternion.Slerp(transform.rotation, mainCam.rotation, smoothTime*Time.fixedDeltaTime);
}
}
but this worked because the cockpit and the camera shared the same centre of rotation.
With my FPS the gun is offset from the centre of the camera: 
I've put the gun inside a parent object with its pivot centred on the camera, and I've used a similar script as before to make the guns' 'MotionPivot' rotate about its own pivot, along with the camera: 
public class GunVrSway : MonoBehaviour {
private Transform mainCam;
private Transform gunPivot;
public float smoothTime = 2.8F;
public float positionOffsetX;
public float positionOffsetY;
public float positionOffsetZ;
void Start () {
mainCam = Camera.main.gameObject.transform;
gunPivot = transform.GetChild(0);
}
void FixedUpdate() {
Vector3 newPos = new Vector3(positionOffsetX, positionOffsetY, positionOffsetZ);
transform.position = mainCam.position + newPos;
transform.localRotation = mainCam.rotation;
gunPivot.localRotation = Quaternion.Slerp(gunPivot.localRotation, mainCam.rotation, smoothTime*Time.fixedDeltaTime);
}
}
but the gun still pivots from left to right of the screen, not along the local axis of the MotionPivot child. I'd like it to stay to the right of the FPS view.
Here's a screencast of the problem (sorry not very good, lots of dropped frames in the screen capture) http://screencast.com/t/GMvs7xqE
Can anyone help? Would be much appreciated.
I'll answer my own question since I eventually found a solution.
First off, the working script was simple enough once I worked out that I needed to match both objects' forward vector rather than their rotation, which is what I'd done with the hub script.
Something that caught me out was that the MotionPivot object (the one assigned to the gunPivot variable in the above script) additionally had animations attached to it (for recoil on firing and reload and idle bobbing). Essentially, two things (script and animation) were trying the move the object at the same time. To get around that I just added an additional empty object in the hierarchy (GunController > SwayPivot > MotionPivot). In the script below, it's SwayPivot which is being referenced, while MotionPivot continues to be moved by the animation clips.
So here's the working script:
using UnityEngine;
using System.Collections;
public class GunVrSway : MonoBehaviour {
private Transform mainCam;
private Transform gunPivot;
public float smoothTime = 5f;
void Start () {
mainCam = Camera.main.gameObject.transform;
gunPivot = transform.GetChild(0);
}
void FixedUpdate() {
// track camera position
transform.position = mainCam.position;
Vector3 currentVector = transform.forward;
Vector3 destinationVector = mainCam.transform.forward;
transform.forward = Vector3.Slerp(currentVector, destinationVector, smoothTime*Time.fixedDeltaTime);
}
}
But probably most interesting, from a VR point of view, is that after having implemented what I wanted, I found that it looked wrong in VR. It made the playback a little laggy/stuttery (I assume because of the additional calculations I was introducing) but most importantly it felt oddly less real.
It's something I then remember hearing about on the excellent voices of vr podcast, you just don't need that kind of extra stuff in VR. The gun movement already feels right because it's following your head movement exactly. Once you introduce the smoothing, that delay just makes it feel wrong.
Lesson learned. I've now removed it.
