アドカレ

KENTOのひとりアドカレ6日目の記事です。
https://qiita.com/advent-calendar/2025/kento

環境情報

ツール/SDK	バージョン
Unity	6000.0.62f1
Meta XR Core SDK	81.0.0
Open XR Plugin	1.16.0
XR Interaction Toolkit	3.0.9
XR Hands	1.7.1

事前準備は以下の通りです。

XR Hands

XR Handsは、OpenXRのHand Tracking Extensionが提供する手や指の関節データを、Unityが統一されたAPIとして扱えるように抽象化した仕組みです。これにより、OpenXR互換デバイスにて、統一された方法でハンドトラッキングのボーン情報を扱えます。

デモ

GIFのようなお絵描きデモを作成していきます。

導入

PackageManager経由でXR Handsを導入します。

ついでにHandVisualizerというサンプルも取得しておきます。

次に、設定からHand Tracking Subsystemを有効化します。

また、OVRManagerのHandTrackingSupportもHandを利用可能な設定に変更します。

実装

まず、XRHandSubsystemを扱いやすくするためのユーティリティークラスを作成します。

using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.XR.Hands;

/// <summary>
/// XRHandSubsystemを扱いやすくするためのユーティリティクラス。
/// </summary>
public class XRHandSubsystemUtility : MonoBehaviour
{
    [SerializeField] private Transform _cameraOffset;

    public static XRHandSubsystemUtility Instance { get; private set; }
    public XRHandSubsystem Subsystem => GetOrUpdateSubsystem();

    public bool IsLeftHandTracked => Subsystem?.leftHand.isTracked ?? false;
    public bool IsRightHandTracked => Subsystem?.rightHand.isTracked ?? false;
    public bool IsSubsystemRunning => Subsystem?.running ?? false;
    public Transform UserLocalSpace => _cameraOffset;

    private XRHandSubsystem _subsystem;
    private readonly List<XRHandSubsystem> _subsystemsReuse = new();


    private void Awake()
    {
        Instance = this;
    }

    private XRHandSubsystem GetOrUpdateSubsystem()
    {
        if (_subsystem is { running: true }) return _subsystem;

        SubsystemManager.GetSubsystems(_subsystemsReuse);
        foreach (var handSubsystem in _subsystemsReuse.Where(handSubsystem => handSubsystem.running))
        {
            _subsystem = handSubsystem;
            return _subsystem;
        }

        _subsystem = null;
        return null;
    }

    private XRHandJoint GetJoint(Handedness handedness, XRHandJointID jointId)
    {
        var hand = handedness == Handedness.Left ? Subsystem.leftHand : Subsystem.rightHand;
        return hand.GetJoint(jointId);
    }

    /// <summary>
    /// ジョイントの姿勢をCameraOffset基準で取得する。
    /// </summary>
    public bool TryGetJointPose(Handedness handedness, XRHandJointID jointId, out Pose pose)
    {
        pose = Pose.identity;
        var joint = GetJoint(handedness, jointId);
        if (!joint.TryGetPose(out var localPose)) return false;

        pose = localPose.GetTransformedBy(_cameraOffset.transform);
        return true;
    }
}

ポイントとして、XR HandsのBone座標は “ユーザーローカル空間(XROrigin配下)” で扱うため、CameraOffsetを基準Transformとして姿勢を変換しています。

このユーティリティークラスを使って、ピンチ処理を作成します。親指と人差し指の距離でピンチを判定するロジックです。

using UnityEngine;
using UnityEngine.XR.Hands;

/// <summary>
/// ピンチの状態。
/// </summary>
public enum PinchState
{
    None,
    Started,
    Holding,
    Ended
}

/// <summary>
/// 独自のピンチ認識を行うクラス。
/// </summary>
public static class CustomPinch
{
    private const float PinchThreshold = 0.02f;
    private static bool _wasPinching;

    /// <summary>
    /// ピンチの状態を取得。
    /// </summary>
    public static PinchState CheckPinch()
    {
        var isPinching = IsPinchDetected();

        if (!_wasPinching && isPinching)
        {
            _wasPinching = true;
            return PinchState.Started;
        }

        if (_wasPinching && isPinching)
        {
            return PinchState.Holding;
        }

        if (_wasPinching && !isPinching)
        {
            _wasPinching = false;
            return PinchState.Ended;
        }

        return PinchState.None;
    }

    private static bool IsPinchDetected()
    {
        var xrHandSubsystemUtility = XRHandSubsystemUtility.Instance;
        if (!xrHandSubsystemUtility.IsRightHandTracked)
        {
            return false;
        }

        var isAbleToGetThumbTip = xrHandSubsystemUtility.TryGetJointPose(
            Handedness.Right,
            XRHandJointID.ThumbTip,
            out Pose thumbTipPose);

        var isAbleToGetIndexTip = xrHandSubsystemUtility.TryGetJointPose(
            Handedness.Right,
            XRHandJointID.IndexTip,
            out Pose indexTipPose);

        if (isAbleToGetThumbTip && isAbleToGetIndexTip)
        {
            var dist = Vector3.Distance(thumbTipPose.position, indexTipPose.position);
            return dist < PinchThreshold;
        }

        return false;
    }
}

最後に、独自のピンチ認識を用いたお絵描き処理です。

using UnityEngine;
using UnityEngine.XR.Hands;

/// <summary>
/// ピンチ操作でTrailRendererを使ったお絵描きを行うクラス。
/// </summary>
public class PinchDrawing : MonoBehaviour
{
    [SerializeField] private GameObject _trailPrefab;

    private GameObject _currentTrailObject;

    private void Update()
    {
        var pinchState = CustomPinch.CheckPinch();

        switch (pinchState)
        {
            case PinchState.Started:
                StartDrawing();
                break;
            case PinchState.Holding:
                UpdateDrawing();
                break;
            case PinchState.Ended:
                EndDrawing();
                break;
        }
    }

    private void StartDrawing()
    {
        _currentTrailObject = Instantiate(_trailPrefab);
        UpdateTrailPosition();
    }

    private void UpdateDrawing()
    {
        if (!_currentTrailObject) return;
        UpdateTrailPosition();
    }

    private void EndDrawing()
    {
        _currentTrailObject = null;
    }

    private void UpdateTrailPosition()
    {
        if (!_currentTrailObject) return;

        var xrHandSubsystemUtility = XRHandSubsystemUtility.Instance;

        if (xrHandSubsystemUtility.TryGetJointPose(
                Handedness.Right,
                XRHandJointID.IndexTip,
                out Pose indexTipPose))
        {
            _currentTrailObject.transform.position = indexTipPose.position;
        }
    }
}

これにて完成です。ボーンの位置で直接判定しているので、シミュレーター上でも動作します。

ここまでの実装はMetaのAPIに依存しないため、OpenXR互換デバイスであればコードを変更することなく動作させることができます。(※OpenXR互換デバイス側で実装ミスがないという前提はあります)

Boneを表示する

このままだと、UnityEditorのシミュレーター上では手がどこにあるのかがわかりません。

そこで、デバッグ用の関節表示用クラスを作成します。(一部UniTaskを使用しています)

using Cysharp.Threading.Tasks;
using UnityEngine;
using UnityEngine.XR.Hands;

/// <summary>
/// デバッグ用の手のジョイント表示を管理するクラス。Editor専用。
/// </summary>
public class HandJointDrawer : MonoBehaviour
{
    [SerializeField] private GameObject _debugDrawPrefab;

    private HandDebugObjects _leftHandDebugObjects;
    private HandDebugObjects _rightHandDebugObjects;

    private async UniTask Start()
    {
        if (!Application.isEditor) return;

        var ct = this.GetCancellationTokenOnDestroy();
        var xrHandSubsystemUtility = XRHandSubsystemUtility.Instance;
        await UniTask.WaitUntil(() => xrHandSubsystemUtility.IsSubsystemRunning, cancellationToken: ct);

        var userLocalSpace = xrHandSubsystemUtility.UserLocalSpace;
        _leftHandDebugObjects ??= new HandDebugObjects(Handedness.Left, userLocalSpace, _debugDrawPrefab);
        _rightHandDebugObjects ??= new HandDebugObjects(Handedness.Right, userLocalSpace, _debugDrawPrefab);

        UpdateJointVisibility(false, Handedness.Left);
        UpdateJointVisibility(false, Handedness.Right);

        SubscribeHandSubsystem();
    }

    private void OnDestroy()
    {
        _leftHandDebugObjects?.OnDestroy();
        _rightHandDebugObjects?.OnDestroy();
        UnsubscribeHandSubsystem();
    }

    private void SubscribeHandSubsystem()
    {
        var xrHandSubsystemUtility = XRHandSubsystemUtility.Instance;
        if (!xrHandSubsystemUtility.IsSubsystemRunning) return;

        xrHandSubsystemUtility.Subsystem.trackingAcquired += OnTrackingAcquired;
        xrHandSubsystemUtility.Subsystem.trackingLost += OnTrackingLost;
        xrHandSubsystemUtility.Subsystem.updatedHands += OnUpdatedHands;
    }

    private void UnsubscribeHandSubsystem()
    {
        var xrHandSubsystemUtility = XRHandSubsystemUtility.Instance;
        if (!xrHandSubsystemUtility.IsSubsystemRunning) return;

        xrHandSubsystemUtility.Subsystem.trackingAcquired -= OnTrackingAcquired;
        xrHandSubsystemUtility.Subsystem.trackingLost -= OnTrackingLost;
        xrHandSubsystemUtility.Subsystem.updatedHands -= OnUpdatedHands;
    }

    private void UpdateJointVisibility(bool isTracked, Handedness handedness)
    {
        var shouldDisplayJoints = isTracked;
        var handDebugObjects = handedness == Handedness.Left ? _leftHandDebugObjects : _rightHandDebugObjects;
        handDebugObjects?.ToggleDebugDrawJoints(shouldDisplayJoints);
    }

    private void OnTrackingAcquired(XRHand hand)
    {
        UpdateJointVisibility(true, hand.handedness);
    }

    private void OnTrackingLost(XRHand hand)
    {
        UpdateJointVisibility(false, hand.handedness);
    }

    private void OnUpdatedHands(
        XRHandSubsystem subsystem,
        XRHandSubsystem.UpdateSuccessFlags updateSuccessFlags,
        XRHandSubsystem.UpdateType updateType)
    {
        if (updateType == XRHandSubsystem.UpdateType.Dynamic) return;

        var leftHandTracked = subsystem.leftHand.isTracked;
        var rightHandTracked = subsystem.rightHand.isTracked;

        UpdateJointVisibility(leftHandTracked, Handedness.Left);
        UpdateJointVisibility(rightHandTracked, Handedness.Right);

        UpdateDebugJoints(subsystem, updateSuccessFlags, leftHandTracked, rightHandTracked);
    }

    private void UpdateDebugJoints(
        XRHandSubsystem subsystem,
        XRHandSubsystem.UpdateSuccessFlags updateSuccessFlags,
        bool leftHandTracked,
        bool rightHandTracked)
    {
        if (leftHandTracked)
        {
            _leftHandDebugObjects?.UpdateJoints(
                subsystem.leftHand,
                (updateSuccessFlags & XRHandSubsystem.UpdateSuccessFlags.LeftHandJoints) != 0,
                true);
        }

        if (rightHandTracked)
        {
            _rightHandDebugObjects?.UpdateJoints(
                subsystem.rightHand,
                (updateSuccessFlags & XRHandSubsystem.UpdateSuccessFlags.RightHandJoints) != 0,
                true);
        }
    }

    private class HandDebugObjects
    {
        private readonly GameObject _drawJointsParent;
        private readonly GameObject[] _drawJoints = new GameObject[XRHandJointID.EndMarker.ToIndex()];
        private readonly LineRenderer[] _lines = new LineRenderer[XRHandJointID.EndMarker.ToIndex()];
        private static readonly Vector3[] LinePointsReuse = new Vector3[2];
        private const float LineWidth = 0.005f;

        public HandDebugObjects(Handedness handedness, Transform parent, GameObject debugDrawPrefab)
        {
            _drawJointsParent = new GameObject
            {
                transform =
                {
                    parent = parent,
                    localPosition = Vector3.zero,
                    localRotation = Quaternion.identity
                },
                name = handedness + "HandDebugDrawJoints"
            };

            for (var jointId = XRHandJointID.BeginMarker; jointId < XRHandJointID.EndMarker; ++jointId)
            {
                var jointIndex = jointId.ToIndex();
                _drawJoints[jointIndex] = Instantiate(debugDrawPrefab);
                _drawJoints[jointIndex].transform.parent = _drawJointsParent.transform;
                _drawJoints[jointIndex].name = jointId.ToString();

                _lines[jointIndex] = _drawJoints[jointIndex].GetComponent<LineRenderer>();
                if (_lines[jointIndex])
                {
                    _lines[jointIndex].startWidth = _lines[jointIndex].endWidth = LineWidth;
                    LinePointsReuse[0] = LinePointsReuse[1] = Vector3.zero;
                    _lines[jointIndex].SetPositions(LinePointsReuse);
                }
            }
        }

        public void OnDestroy()
        {
            for (var jointIndex = 0; jointIndex < _drawJoints.Length; ++jointIndex)
            {
                if (!_drawJoints[jointIndex]) continue;

                Destroy(_drawJoints[jointIndex]);
                _drawJoints[jointIndex] = null;
            }

            if (_drawJointsParent)
            {
                Destroy(_drawJointsParent);
            }
        }

        public void ToggleDebugDrawJoints(bool debugDrawJoints)
        {
            for (var jointIndex = 0; jointIndex < _drawJoints.Length; ++jointIndex)
            {
                if (_drawJoints[jointIndex])
                {
                    ToggleRenderers<MeshRenderer>(debugDrawJoints, _drawJoints[jointIndex].transform);
                    if (_lines[jointIndex])
                    {
                        _lines[jointIndex].enabled = debugDrawJoints;
                    }
                }
            }

            if (_lines.Length > 0 && _lines[0])
            {
                _lines[0].enabled = false;
            }
        }

        public void UpdateJoints(XRHand hand, bool areJointsTracked, bool debugDrawJoints)
        {
            if (!areJointsTracked) return;

            var wristPose = Pose.identity;
            var parentIndex = XRHandJointID.Wrist.ToIndex();
            UpdateJoint(debugDrawJoints, hand.GetJoint(XRHandJointID.Wrist), ref wristPose, ref parentIndex);
            UpdateJoint(debugDrawJoints, hand.GetJoint(XRHandJointID.Palm), ref wristPose, ref parentIndex, false);

            for (var fingerIndex = (int)XRHandFingerID.Thumb; fingerIndex <= (int)XRHandFingerID.Little; ++fingerIndex)
            {
                var parentPose = wristPose;
                var fingerId = (XRHandFingerID)fingerIndex;
                parentIndex = XRHandJointID.Wrist.ToIndex();

                var jointIndexBack = fingerId.GetBackJointID().ToIndex();
                for (var jointIndex = fingerId.GetFrontJointID().ToIndex(); jointIndex <= jointIndexBack; ++jointIndex)
                {
                    UpdateJoint(
                        debugDrawJoints,
                        hand.GetJoint(XRHandJointIDUtility.FromIndex(jointIndex)),
                        ref parentPose,
                        ref parentIndex);
                }
            }
        }

        private void UpdateJoint(
            bool debugDrawJoints,
            XRHandJoint joint,
            ref Pose parentPose,
            ref int parentIndex,
            bool cacheParentPose = true)
        {
            if (joint.id == XRHandJointID.Invalid) return;

            var jointIndex = joint.id.ToIndex();

            if (!joint.TryGetPose(out var pose)) return;

            if (_drawJoints[jointIndex])
            {
                _drawJoints[jointIndex].transform.localPosition = pose.position;
                _drawJoints[jointIndex].transform.localRotation = pose.rotation;

                if (debugDrawJoints && joint.id != XRHandJointID.Wrist && _lines[jointIndex] != null)
                {
                    LinePointsReuse[0] = _drawJoints[parentIndex].transform.position;
                    LinePointsReuse[1] = _drawJoints[jointIndex].transform.position;
                    _lines[jointIndex].SetPositions(LinePointsReuse);
                }
            }

            if (cacheParentPose)
            {
                parentPose = pose;
                parentIndex = jointIndex;
            }
        }

        private static void ToggleRenderers<TRenderer>(bool toggle, Transform rendererTransform)
            where TRenderer : Renderer
        {
            if (rendererTransform.TryGetComponent<TRenderer>(out var renderer))
                renderer.enabled = toggle;

            for (var childIndex = 0; childIndex < rendererTransform.childCount; ++childIndex)
                ToggleRenderers<TRenderer>(toggle, rendererTransform.GetChild(childIndex));
        }
    }
}

上記コードは以下のサンプルコードを参考に実装しています。
Assets/Samples/XR Hands/1.7.1/HandVisualizer/Scripts/HandVisualizer.cs

以下パスにジョイント用のPrefabも用意されています。
Assets/Samples/XR Hands/1.7.1/HandVisualizer/Prefabs/Joint.prefab

実行するとこのような感じで手の位置が可視化されます。

XRCommonHandGestures

ここまで、ピンチ処理を自前実装してきましたが、XRHandSubSystem内にあらかじめXRCommonHandGesturesというクラスが実装されています。

このクラスを使えば各プラットフォームがネイティブで定義した共通ジェスチャー処理の色々を簡単に取得できます。

注意点として、XRCommonHandGesturesはXR Device Simulator上では動作しません。

XRHandSubsystemに実装されているので、XRHandSubsystemUtilityに呼び出し処理を追加します。

using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.XR.Hands;

/// <summary>
/// XRHandSubsystemを扱いやすくするためのユーティリティクラス。
/// </summary>
public class XRHandSubsystemUtility : MonoBehaviour
{
    [SerializeField] private Transform _cameraOffset;

    public static XRHandSubsystemUtility Instance { get; private set; }
    public XRHandSubsystem Subsystem => GetOrUpdateSubsystem();

    public bool IsLeftHandTracked => Subsystem?.leftHand.isTracked ?? false;
    public bool IsRightHandTracked => Subsystem?.rightHand.isTracked ?? false;
    public bool IsSubsystemRunning => Subsystem?.running ?? false;
    public Transform UserLocalSpace => _cameraOffset;

    private XRHandSubsystem _subsystem;
    private readonly List<XRHandSubsystem> _subsystemsReuse = new();


    private void Awake()
    {
        Instance = this;
    }

    private XRHandSubsystem GetOrUpdateSubsystem()
    {
        if (_subsystem is { running: true }) return _subsystem;

        SubsystemManager.GetSubsystems(_subsystemsReuse);
        foreach (var handSubsystem in _subsystemsReuse.Where(handSubsystem => handSubsystem.running))
        {
            _subsystem = handSubsystem;
            return _subsystem;
        }

        _subsystem = null;
        return null;
    }

    private XRHandJoint GetJoint(Handedness handedness, XRHandJointID jointId)
    {
        var hand = handedness == Handedness.Left ? Subsystem.leftHand : Subsystem.rightHand;
        return hand.GetJoint(jointId);
    }

    /// <summary>
    /// ジョイントの姿勢をCameraOffset基準で取得する。
    /// </summary>
    public bool TryGetJointPose(Handedness handedness, XRHandJointID jointId, out Pose pose)
    {
        pose = Pose.identity;
        var joint = GetJoint(handedness, jointId);
        if (!joint.TryGetPose(out var localPose)) return false;
        pose = localPose.GetTransformedBy(_cameraOffset.transform);
        return true;
    }
    
+   /// <summary>
+   /// CommonGesturesからピンチ箇所の姿勢をCameraOffset基準で取得する。
+   /// </summary>
+   public bool TryGetPinchPoseFromCommonGesture(Handedness handedness, out Pose pose)
+   {
+       var commonGestures = handedness == Handedness.Left
+           ? Subsystem.leftHandCommonGestures
+           : Subsystem.rightHandCommonGestures;
+        
+       var success = commonGestures.TryGetPinchPose(out var localPose);
+       pose = success ? localPose.GetTransformedBy(_cameraOffset.transform) : Pose.identity;
+       return success;
+   }
}

次に、PinchGestureの代わりに、CommonGestureを利用する形式のクラスを作成します。TryGetPinchValueでピンチジェスチャーの度合を0~1で取得できます。

/// <summary>
/// XRCommonHandGesturesを使用したピンチ認識を行うクラス。
/// </summary>
public static class CustomCommonGesturesPinch
{
    private const float PinchThreshold = 0.8f;
    private const float ReleaseThreshold = 0.3f;
    private static bool _wasPinching;

    /// <summary>
    /// ピンチの状態を取得。
    /// </summary>
    public static PinchState CheckPinch()
    {
        var isPinching = IsPinchDetected();

        if (!_wasPinching && isPinching)
        {
            _wasPinching = true;
            return PinchState.Started;
        }

        if (_wasPinching && isPinching)
        {
            return PinchState.Holding;
        }

        if (_wasPinching && !isPinching)
        {
            _wasPinching = false;
            return PinchState.Ended;
        }

        return PinchState.None;
    }

    private static bool IsPinchDetected()
    {
        var commonHandGestures = XRHandSubsystemUtility.Instance.Subsystem.rightHandCommonGestures;
        if (!commonHandGestures.TryGetPinchValue(out var pinchValue)) return false;
        
        // 押下時は高い閾値、離す時は低い閾値。
        if (_wasPinching)
        {
            return pinchValue > ReleaseThreshold;
        }
        
        return pinchValue >= PinchThreshold;
    }
}

最後に修正した処理をお絵描き処理で呼び出します。

using UnityEngine;
using UnityEngine.XR.Hands;

/// <summary>
/// ピンチ操作でTrailRendererを使ったお絵描きを行うクラス。
/// </summary>
public class PinchDrawing : MonoBehaviour
{
    [SerializeField] private GameObject _trailPrefab;

    private GameObject _currentTrailObject;

    private void Update()
    {
-       var pinchState = CustomPinch.CheckPinch();
+       var pinchState = CustomCommonGesturesPinch.CheckPinch();
        
        switch (pinchState)
        {
            case PinchState.Started:
                StartDrawing();
                break;
            case PinchState.Holding:
                UpdateDrawing();
                break;
            case PinchState.Ended:
                EndDrawing();
                break;
        }
    }

    private void StartDrawing()
    {
        _currentTrailObject = Instantiate(_trailPrefab);
        UpdateTrailPosition();
    }

    private void UpdateDrawing()
    {
        if (!_currentTrailObject) return;
        UpdateTrailPosition();
    }

    private void EndDrawing()
    {
        _currentTrailObject = null;
    }

    private void UpdateTrailPosition()
    {
        if (!_currentTrailObject) return;

        var xrHandSubsystemUtility = XRHandSubsystemUtility.Instance;

-       if (xrHandSubsystemUtility.TryGetJointPose(
-               Handedness.Right,
-               XRHandJointID.IndexTip,
-               out Pose indexTipPose))
-       {
-           _currentTrailObject.transform.position = indexTipPose.position;
-       }

+       if (xrHandSubsystemUtility.TryGetPinchPoseFromCommonGesture(Handedness.Right, out var pose))
+       {
+           _currentTrailObject.transform.position = pose.position;
+       }
    }
}

今回はピンチジェスチャーですが、他にもよく使うジェスチャーが用意されており、大変便利でした。