Hololens开发笔记之Gesture手势识别（手势检测反馈）

本文实现当使用者手出现在Hololens视野范围内时，跟踪手并给出反馈的效果。

1、在Manager上添加HandsManager脚本组件，用于追踪识别手

HandsManager.cs如下（直接使用HoloTooKit中脚本）

// Copyright (c) Microsoft Corporation. All rights reserved.  
// Licensed under the MIT License. See LICENSE in the project root for license information.  
  
using System.Collections.Generic;  
using UnityEngine.VR.WSA.Input;  
  
namespace HoloToolkit.Unity  
{  
    /// <summary>  
    /// HandsManager determines if the hand is currently detected or not.  
    /// </summary>  
    public partial class HandsManager : Singleton<HandsManager>  
    {  
        /// <summary>  
        /// HandDetected tracks the hand detected state.  
        /// Returns true if the list of tracked hands is not empty.  
        /// </summary>  
        public bool HandDetected  
        {  
            get { return trackedHands.Count > 0; }  
        }  
  
        private HashSet<uint> trackedHands = new HashSet<uint>();  
  
        void Awake()  
        {  
            //识别到来源  
            InteractionManager.SourceDetected += InteractionManager_SourceDetected;  
            //来源丢失  
            InteractionManager.SourceLost += InteractionManager_SourceLost;  
        }  
  
        private void InteractionManager_SourceDetected(InteractionSourceState state)  
        {  
            // 检测来源是否为手，如果是手则加入跟踪集合  
            if (state.source.kind != InteractionSourceKind.Hand)  
            {  
                return;  
            }  
  
            trackedHands.Add(state.source.id);  
        }  
  
        private void InteractionManager_SourceLost(InteractionSourceState state)  
        {  
            // 检测丢失的来源是否为手，如果是手则从跟踪集合中去除  
            if (state.source.kind != InteractionSourceKind.Hand)  
            {  
                return;  
            }  
  
            if (trackedHands.Contains(state.source.id))  
            {  
                trackedHands.Remove(state.source.id);  
            }  
        }  
  
        void OnDestroy()  
        {  
            InteractionManager.SourceDetected -= InteractionManager_SourceDetected;  
            InteractionManager.SourceLost -= InteractionManager_SourceLost;  
        }  
    }  
}

该脚本中使用到了底层API Interaction Input

底层API运行获得输入来源的更多详细信息，例如它在世界中的位置和速度。

如何处理底层交互事件
使用底层交互是很容易的：
1）注册InteractionManager事件
2）处理事件
停止它也很容易：
1）取消注册事件

处理底层交互事件
一旦注册了底层交互事件，在事件发生时你就可以得到回调。你可以使用获取到的时间信息来处理应用行为。

void InteractionManager_SourcePressed(InteractionSourceState state)  
{  
// state变量里包含以下信息:  
// 当前凝视射线信息  
// 来源是否被点击  
// 位置、速度之类的属性  
// 来源id和来源类型 （ hand, voice, controller或其他）  
}

如何停止交互事件
当你不再想要关注一些事件后，只需要取消时间注册即可。

InteractionManager.SourcePressed -= InteractionManager_SourcePressed;

输入源变化事件
这些事件描述了输入源的当前状态：
1) detected（即将激活）
2) lost（即将取消激活）
3) updates（移动或者一些状态在变化）
4) is pressed（点击、按钮按下或者语音选中）
5) is released（点击结束，按钮松开，语音选中结束）

输入源状态
每个事件都会有一个InteractionSourceState参数，这个参数代表了实时输入源状态：
1) 是否是点击状态
2) InteractionSourceProperties包含了输入源位置信息 InteractionSourceLocation，能够获得当前输入源位置和速度信息
3) 凝视射线信息，用于判断事件发生时用户是否在注视目标
4) 来源类型信息，包括hand、voice、controller或者其他类型

2、在Cursor下新建Empty对象，并重命名为CursorBillboard，并添加Billboard脚本组件

Billboard脚本如下(可以直接在HoloToolKit中找到)

// Copyright (c) Microsoft Corporation. All rights reserved.  
// Licensed under the MIT License. See LICENSE in the project root for license information.  
  
using UnityEngine;  
  
namespace HoloToolkit.Unity  
{  
    public enum PivotAxis  
    {  
        // Rotate about all axes.  
        Free,  
        // Rotate about an individual axis.  
        X,  
        Y  
    }  
  
    /// <summary>  
    /// The Billboard class implements the behaviors needed to keep a GameObject  
    /// oriented towards the user.  
    /// </summary>  
    public class Billboard : MonoBehaviour  
    {  
        /// <summary>  
        /// The axis about which the object will rotate.  
        /// </summary>  
        [Tooltip("Specifies the axis about which the object will rotate (Free rotates about both X and Y).")]  
        public PivotAxis PivotAxis = PivotAxis.Free;  
  
        /// <summary>  
        /// Overrides the cached value of the GameObject's default rotation.  
        /// </summary>  
        public Quaternion DefaultRotation { get; private set; }  
  
        private void Awake()  
        {  
            // Cache the GameObject's default rotation.  
            DefaultRotation = gameObject.transform.rotation;  
        }  
  
        /// <summary>  
        /// Keeps the object facing the camera.  
        /// </summary>  
        private void Update()  
        {  
            // Get a Vector that points from the Camera to the target.  
            Vector3 forward;  
            Vector3 up;  
  
            // Adjust for the pivot axis. We need a forward and an up for use with Quaternion.LookRotation  
            switch (PivotAxis)  
            {  
                // If we're fixing one axis, then we're projecting the camera's forward vector onto  
                // the plane defined by the fixed axis and using that as the new forward.  
                case PivotAxis.X:  
                    Vector3 right = transform.right; // Fixed right  
                    forward = Vector3.ProjectOnPlane(Camera.main.transform.forward, right).normalized;  
                    up = Vector3.Cross(forward, right); // Compute the up vector  
                    break;  
  
                case PivotAxis.Y:  
                    up = transform.up; // Fixed up  
                    forward = Vector3.ProjectOnPlane(Camera.main.transform.forward, up).normalized;  
                    break;  
  
                // If the axes are free then we're simply aligning the forward and up vectors  
                // of the object with those of the camera.   
                case PivotAxis.Free:  
                default:  
                    forward = Camera.main.transform.forward;  
                    up = Camera.main.transform.up;  
                    break;  
            }  
  
  
            // Calculate and apply the rotation required to reorient the object  
            transform.rotation = Quaternion.LookRotation(forward, up);  
        }  
    }  
}

3、在Cursor上添加CursorFeedback脚本组件

1）在HoloToolkit -> Input -> Prefabs中找到HandDetectedFeedback Prefab 并拖到CursorFeedback的hand detected asset上

2）将刚才创建的CursorBillboard拖到CursorFeedback的Feedback Parent上

CursorFeedback脚本如下（(可以直接在HoloToolKit中找到)）

// Copyright (c) Microsoft Corporation. All rights reserved.  
// Licensed under the MIT License. See LICENSE in the project root for license information.  
  
using UnityEngine;  
  
namespace HoloToolkit.Unity  
{  
    /// <summary>  
    /// CursorFeedback class takes GameObjects to give cursor feedback  
    /// to users based on different states.  
    /// </summary>  
    public class CursorFeedback : MonoBehaviour  
    {  
        [Tooltip("Drag a prefab object to display when a hand is detected.")]  
        public GameObject HandDetectedAsset;  
        private GameObject handDetectedGameObject;  
  
        [Tooltip("Drag a prefab object to parent the feedback assets.")]  
        public GameObject FeedbackParent;  
  
        void Awake()  
        {  
            if (HandDetectedAsset != null)  
            {  
                handDetectedGameObject = InstantiatePrefab(HandDetectedAsset);  
            }  
            else  
            {  
                Debug.LogError("Missing a required game object asset.  Check HandDetectedAsset is not null in editor.");  
            }  
        }  
  
        private GameObject InstantiatePrefab(GameObject inputPrefab)  
        {  
            GameObject instantiatedPrefab = null;  
  
            if (inputPrefab != null && FeedbackParent != null)  
            {  
                instantiatedPrefab = GameObject.Instantiate(inputPrefab);  
                // Assign parent to be the FeedbackParent  
                // so that feedback assets move and rotate with this parent.  
                instantiatedPrefab.transform.parent = FeedbackParent.transform;  
  
                // Set starting state of the prefab's GameObject to be inactive.  
                instantiatedPrefab.gameObject.SetActive(false);  
            }  
            else  
            {  
                Debug.LogError("Missing a required game object asset.  Check FeedbackParent is not null in editor.");  
            }  
  
            return instantiatedPrefab;  
        }  
  
        void Update()  
        {  
            UpdateHandDetectedState();  
        }  
  
        private void UpdateHandDetectedState()  
        {  
            if (handDetectedGameObject == null)  
            {  
                return;  
            }  
  
            handDetectedGameObject.SetActive(HandsManager.Instance.HandDetected);  
        }  
    }  
}

4、运行测试

当手出现在Hololens视野中时，手被检测到，在凝视射线处出现一个蓝色的小手（Hololens模拟器中需要处于hold状态才会出现蓝色小手，真机上只要手举起就可以）