unity 保持物体大小不变

    /// <summary>
    /// 在透视投影时，改变相机的fov或物体的位置，让物体保持在屏幕上看起来的大小一样的缩放值
    /// </summary>
    /// <returns></returns>
    public static float KeepSizeLookSameScale(Vector3 pos, Camera cam)
    {
        float distance = Vector3.Distance(cam.transform.position, pos);
        float size = distance * Mathf.Tan(cam.fieldOfView * 0.5f * Mathf.Deg2Rad);

        float max = 100f * Mathf.Tan(122 * 0.5f * Mathf.Deg2Rad);

        float scale = size / max;
        //scale = Mathf.Clamp(scale, 0.01f, 0.1f);//限定一个最大值和最小值
        return scale;
    }