Implementation of simple gain locomotion (originally described in this talk at Vision Summit 2016: https://www.youtube.com/watch?v=At_Zac4Xezw)

SimpleGainLocomotion.cs

using UnityEngine;

public class SimpleGainLocomotion : MonoBehaviour
{
    public Transform Head;
    public float Gain = 1f;
    
    void Update()
    {
        Vector3 localPlayerPosition = this.transform.InverseTransformPoint(this.Head.position);
        Vector3 floorPosition = new Vector3(localPlayerPosition.x, 0f, localPlayerPosition.z);

        this.transform.localPosition = this.Gain * floorPosition;
    }
    
    #region Debug visualization

    void OnDrawGizmos()
    {
        if (!this.isActiveAndEnabled)
            return;

        Vector3 localPlayerPosition = this.transform.InverseTransformPoint(this.Head.position);
        Gizmos.color = Color.white;
        Gizmos.DrawLine(this.Head.position, localPlayerPosition);

        var playArea = this.GetComponent<SteamVR_PlayArea>();
        if (playArea != null)
        {
            Gizmos.color = Color.green;
            DrawWireframe(playArea.vertices, this.Gain + 1f);
        }

    }

    public void DrawWireframe(Vector3[] vertices, float scale)
    {
        if (vertices == null || vertices.Length == 0)
            return;

        var offset = transform.TransformVector(Vector3.up * 2f);
        for (int i = 0; i < 4; i++)
        {
            int next = (i + 1) % 4;

            var a = vertices[i] * scale;
            var b = a + offset;
            var c = vertices[next] * scale;
            var d = c + offset;
            Gizmos.DrawLine(a, b);
            Gizmos.DrawLine(a, c);
            Gizmos.DrawLine(b, d);
        }
    }
    
    #endregion
}