{"category": "Unity Engine/Editor/Extensions", "keywords": "Unity, Editor, AnimationClip, Preview, UI"} An `AnimationClip` preview UI component that can be embedded into other `Editor`s.

MotionPreview.cs

using System;
using UnityEditor.Animations;
using UnityEngine;
using Object = UnityEngine.Object;

// NOTE: The Reflector.cs is here: https://gist.github.com/SolarianZ/e8980ee322182a76745e6cb5aac99b4d 

// Usage(function calling hierarchy):
//   1. YourCustomInpector.OnEnable() -> _motionPreview = new MotionPreview();
//   2. YourCustomInpector.OnPreviewSettings() -> _motionPreview.OnPreviewSettings();
//   3. YourCustomInpector.OnInteractivePreviewGUI() -> _motionPreview.OnInteractivePreviewGUI();
//   4. YourCustomInpector.OnDisable() -> _motionPreview.OnDisable();
//   5. YourCustomInpector.OnTargetMotionChanged() -> _motionPreview.Initialize(targetMotion);

// OPTIMIZABLE: This class extensively uses reflection. If you want to improve the performance of this class, you can use the Reflector.CreateDelegate method to reduce the amount of reflection used. 

public class MotionPreview
{
    private object _avatarPreviewObj;

    private Motion _motion;
    private AnimatorController _controller;
    private AnimatorStateMachine _stateMachine;
    private AnimatorState _state;
    private bool _prevIKOnFeet;
    private bool _controllerIsDirty;
    private Action _controllerDirtyDelegate;
    private Delegate _onPreviewAvatarChangedDelegate;


    public void Initialize(Motion motion)
    {
        _motion = motion;

        if (_avatarPreviewObj == null)
        {
            _avatarPreviewObj = Reflector.CreateInstance(typeof(UnityEditor.Editor).Assembly,
                "UnityEditor.AvatarPreview", new object[] { null, _motion });
            _avatarPreviewObj.Set("OnAvatarChangeFunc", GetOnPreviewAvatarChangedDelegate());
            _avatarPreviewObj.Invoke("ResetPreviewFocus", null);
            _prevIKOnFeet = (bool)_avatarPreviewObj.Get("IKOnFeet");
        }

        ResetStateMachine();
    }

    public void OnDisable()
    {
        ClearStateMachine();

        if (_avatarPreviewObj != null)
        {
            _avatarPreviewObj.Invoke("OnDisable", null);
            _avatarPreviewObj = null;
        }
    }

    public float GetCurrentTime()
    {
        if (_avatarPreviewObj == null)
        {
            return 0;
        }

        var timeControlObj = _avatarPreviewObj.Get("timeControl");
        return (float)timeControlObj.Get("currentTime");
    }

    public void SetCurrentTime(float time)
    {
        if (_avatarPreviewObj == null)
        {
            return;
        }

        var timeControlObj = _avatarPreviewObj.Get("timeControl");
        timeControlObj.Set("currentTime", time);
    }

    public float GetNormalizedTime()
    {
        if (_avatarPreviewObj == null)
        {
            return 0;
        }

        var timeControlObj = _avatarPreviewObj.Get("timeControl");
        return (float)timeControlObj.Get("normalizedTime");
    }

    public void SetNormalizedTime(float time)
    {
        if (_avatarPreviewObj == null)
        {
            return;
        }

        var timeControlObj = _avatarPreviewObj.Get("timeControl");
        timeControlObj.Set("normalizedTime", time);
    }

    public void SetNextNormalizedTime(float time)
    {
        if (_avatarPreviewObj == null)
        {
            return;
        }

        var timeControlObj = _avatarPreviewObj.Get("timeControl");
        timeControlObj.Set("nextCurrentTime", time);
    }

    public void ResetStateMachine()
    {
        ClearStateMachine();
        CreateStateMachine();
    }

    private void CreateStateMachine()
    {
        if (_avatarPreviewObj == null) return;

        var previewAnimator = _avatarPreviewObj.Get("Animator") as Animator;
        if (!previewAnimator) return;

        if (_controller == null)
        {
            _controller = new AnimatorController();
            _controller.Set("pushUndo", false);
            _controller.AddLayer("preview");
            _stateMachine = _controller.layers[0].stateMachine;
            _stateMachine.Set("pushUndo", false);

            _state = _stateMachine.AddState("preview");
            _state.Set("pushUndo", false);
            _state.motion = _motion;
            _state.iKOnFeet = (bool)_avatarPreviewObj.Get("IKOnFeet");

            _state.hideFlags = HideFlags.HideAndDontSave;
            _controller.hideFlags = HideFlags.HideAndDontSave;
            _stateMachine.hideFlags = HideFlags.HideAndDontSave;

            AnimatorController.SetAnimatorController(previewAnimator, _controller);
            _controller.Set("OnAnimatorControllerDirty", GetControllerDirtyDelegate());

            _controllerIsDirty = false;
        }

        var effectiveAnimatorController = Reflector.Invoke(typeof(AnimatorController), null,
            "GetEffectiveAnimatorController", new object[] { previewAnimator });
        if (!ReferenceEquals(effectiveAnimatorController, _controller))
            AnimatorController.SetAnimatorController(previewAnimator, _controller);
    }

    private void ClearStateMachine()
    {
        if (_avatarPreviewObj != null)
        {
            var previewAnimator = _avatarPreviewObj.Get("Animator") as Animator;
            if (previewAnimator)
            {
                AnimatorController.SetAnimatorController(previewAnimator, null);
            }
        }

        if (_controller)
        {
            _controller.Set("OnAnimatorControllerDirty", null);
        }

        Object.DestroyImmediate(_controller);
        Object.DestroyImmediate(_state);
        _stateMachine = null;
        _controller = null;
        _state = null;
    }


    protected virtual void ControllerDirty()
    {
        _controllerIsDirty = true;
    }

    private void OnPreviewAvatarChanged()
    {
        ResetStateMachine();
    }

    private Action GetControllerDirtyDelegate()
    {
        if (_controllerDirtyDelegate == null)
        {
            _controllerDirtyDelegate = ControllerDirty;
        }

        return _controllerDirtyDelegate;
    }

    private Delegate GetOnPreviewAvatarChangedDelegate()
    {
        if (_onPreviewAvatarChangedDelegate == null)
        {
            //m_onPreviewAvatarChangedDelegate = OnPreviewAvatarChanged;
            var delegateType = Reflector.GetType(typeof(UnityEditor.Editor).Assembly, "UnityEditor.AvatarPreview+OnAvatarChange");
            _onPreviewAvatarChangedDelegate = this.CreateDelegate(nameof(OnPreviewAvatarChanged), delegateType);
        }

        return _onPreviewAvatarChangedDelegate;
    }


    public bool HasPreviewGUI()
    {
        return true;
    }

    public void OnPreviewSettings()
    {
        if (_avatarPreviewObj == null)
        {
            return;
        }

        _avatarPreviewObj.Invoke("DoPreviewSettings", null);
    }

    public void OnInteractivePreviewGUI(Rect r, GUIStyle background)
    {
        if (_avatarPreviewObj == null)
        {
            return;
        }

        UpdateAvatarState();

        _avatarPreviewObj.Invoke("DoAvatarPreview", new object[] { r, background });
    }

    private void UpdateAvatarState()
    {
        if (UnityEngine.Event.current.type != EventType.Repaint)
        {
            return;
        }

        if (_avatarPreviewObj.Get("PreviewObject") == null || _controllerIsDirty)
        {
            _avatarPreviewObj.Invoke("ResetPreviewInstance", null);
            if (_avatarPreviewObj.Get("PreviewObject") != null)
            {
                ResetStateMachine();
            }
        }

        var previewAnimator = _avatarPreviewObj.Get("Animator") as Animator;
        if (!previewAnimator)
        {
            return;
        }

        var timeControlObj = _avatarPreviewObj.Get("timeControl");
        var ikOnFeet = (bool)_avatarPreviewObj.Get("IKOnFeet");
        if (_prevIKOnFeet != ikOnFeet)
        {
            _prevIKOnFeet = ikOnFeet;
            Vector3 prevPos = previewAnimator.rootPosition;
            Quaternion prevRotation = previewAnimator.rootRotation;
            ResetStateMachine();
            previewAnimator.Update(GetCurrentTime());
            previewAnimator.Update(0); // forces deltaPos/Rot to 0,0,0
            previewAnimator.rootPosition = prevPos;
            previewAnimator.rootRotation = prevRotation;
        }

        timeControlObj.Set("loop", true);

        float stateLength = 1.0f;
        float stateTime = 0.0f;

        if (previewAnimator.layerCount > 0)
        {
            AnimatorStateInfo stateInfo = previewAnimator.GetCurrentAnimatorStateInfo(0);
            stateLength = stateInfo.length;
            stateTime = stateInfo.normalizedTime;
        }

        timeControlObj.Set("startTime", 0f);
        timeControlObj.Set("stopTime", stateLength);
        timeControlObj.Invoke("Update", null);

        float deltaTime = (float)timeControlObj.Get("deltaTime");

        if (!_motion || !_motion.isLooping)
        {
            if (stateTime >= 1.0f)
            {
                deltaTime -= stateLength;
            }
            else if (stateTime < 0.0f)
            {
                deltaTime += stateLength;
            }
        }

        previewAnimator.Update(deltaTime);
    }
}

CHANGELOG

Revision 7

• Update comment

Revision 6

• Add SetNextNormalizedTime method

Revision 5

• Restore comments

Revision 4

• Fix the issue where the preview view does not refresh after the motion changes

Revision 3

• Handle exceptions

Revision 2

• Rename file

Revision 1

• Initial commit