XiuXianGame/Packages/com.kybernetik.animancer/Editor/GUI/Field Drawers/Transitions/ManualMixerTransitionDrawer.cs

// Animancer // https://kybernetik.com.au/animancer // Copyright 2018-2024 Kybernetik //

#if UNITY_EDITOR && UNITY_IMGUI

using Animancer.Units.Editor;
using System;
using System.Collections.Generic;
using UnityEditor;
using UnityEditorInternal;
using UnityEngine;
using static Animancer.Editor.AnimancerGUI;
using Object = UnityEngine.Object;

namespace Animancer.Editor
{
    /// <inheritdoc/>
    /// https://kybernetik.com.au/animancer/api/Animancer.Editor/ManualMixerTransitionDrawer
    [CustomPropertyDrawer(typeof(ManualMixerTransition), true)]
    public class ManualMixerTransitionDrawer : TransitionDrawer
    {
        /************************************************************************************************************************/

        /// <summary>Should two lines be used to draw each child?</summary>
        public static readonly BoolPref
            TwoLineMode = new(
                nameof(ManualMixerTransitionDrawer) + "." + nameof(TwoLineMode),
                "Two Line Mode",
                true);

        /************************************************************************************************************************/

        /// <summary>The property currently being drawn.</summary>
        /// <remarks>
        /// Normally each property has its own drawer,
        /// but arrays share a single drawer for all elements.
        /// </remarks>
        public static SerializedProperty CurrentProperty { get; private set; }

        /// <summary>The <see cref="ManualMixerTransition{TState}.Animations"/> field.</summary>
        public static SerializedProperty CurrentAnimations { get; private set; }

        /// <summary>The <see cref="ManualMixerTransition{TState}.Speeds"/> field.</summary>
        public static SerializedProperty CurrentSpeeds { get; private set; }

        /// <summary>The <see cref="ManualMixerTransition{TState}.SynchronizeChildren"/> field.</summary>
        public static SerializedProperty CurrentSynchronizeChildren { get; private set; }

        private readonly Dictionary<string, ReorderableList>
            PropertyPathToStates = new();

        private ReorderableList _MultiSelectDummyList;

        /************************************************************************************************************************/

        /// <summary>Gather the details of the `property`.</summary>
        /// <remarks>
        /// This method gets called by every <see cref="GetPropertyHeight"/> and <see cref="OnGUI"/> call since
        /// Unity uses the same <see cref="PropertyDrawer"/> instance for each element in a collection, so it
        /// needs to gather the details associated with the current property.
        /// </remarks>
        protected virtual ReorderableList GatherDetails(SerializedProperty property)
        {
            InitializeMode(property);
            GatherSubProperties(property);

            if (property.hasMultipleDifferentValues)
            {
                return _MultiSelectDummyList ??= new(new List<Object>(), typeof(Object))
                {
                    elementHeight = LineHeight,
                    displayAdd = false,
                    displayRemove = false,
                    footerHeight = 0,
                    drawHeaderCallback = DoAnimationHeaderGUI,
                    drawNoneElementCallback = area
                        => EditorGUI.LabelField(area, "Multi-editing animations is not supported"),
                };
            }

            if (CurrentAnimations == null)
                return null;

            var path = property.propertyPath;

            if (!PropertyPathToStates.TryGetValue(path, out var states))
            {
                states = new(CurrentAnimations.serializedObject, CurrentAnimations)
                {
                    drawHeaderCallback = DoChildListHeaderGUI,
                    elementHeightCallback = GetElementHeight,
                    drawElementCallback = DoElementGUI,
                    onAddCallback = OnAddElement,
                    onRemoveCallback = OnRemoveElement,
                    onReorderCallbackWithDetails = OnReorderList,
                    drawFooterCallback = DoChildListFooterGUI,
                };

                PropertyPathToStates.Add(path, states);
            }

            states.serializedProperty = CurrentAnimations;

            return states;
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Called every time a `property` is drawn to find the relevant child properties and store them to be
        /// used in <see cref="GetPropertyHeight"/> and <see cref="OnGUI"/>.
        /// </summary>
        protected virtual void GatherSubProperties(SerializedProperty property)
        {
            CurrentProperty = property;
            CurrentAnimations = property.FindPropertyRelative(ManualMixerTransition.AnimationsField);
            CurrentSpeeds = property.FindPropertyRelative(ManualMixerTransition.SpeedsField);
            CurrentSynchronizeChildren = property.FindPropertyRelative(ManualMixerTransition.SynchronizeChildrenField);

            if (!property.hasMultipleDifferentValues &&
                CurrentAnimations != null &&
                CurrentSpeeds != null &&
                CurrentSpeeds.arraySize != 0)
                CurrentSpeeds.arraySize = CurrentAnimations.arraySize;
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Adds a menu item that will call <see cref="GatherSubProperties"/> then run the specified
        /// `function`.
        /// </summary>
        protected void AddPropertyModifierFunction(GenericMenu menu, string label,
            MenuFunctionState state, Action<SerializedProperty> function)
        {
            Serialization.AddPropertyModifierFunction(menu, CurrentProperty, label, state, (property) =>
            {
                GatherSubProperties(property);
                function(property);
            });
        }

        /// <summary>
        /// Adds a menu item that will call <see cref="GatherSubProperties"/> then run the specified
        /// `function`.
        /// </summary>
        protected void AddPropertyModifierFunction(GenericMenu menu, string label,
            Action<SerializedProperty> function)
        {
            Serialization.AddPropertyModifierFunction(menu, CurrentProperty, label, (property) =>
            {
                GatherSubProperties(property);
                function(property);
            });
        }

        /************************************************************************************************************************/

        /// <inheritdoc/>
        public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
        {
            var height = EditorGUI.GetPropertyHeight(property, label);

            if (property.isExpanded)
            {
                var states = GatherDetails(property);
                if (states != null)
                    height += StandardSpacing +
                        states.GetHeight();

                if (CurrentAnimations != null)
                    height -= StandardSpacing +
                        EditorGUI.GetPropertyHeight(CurrentAnimations, label);

                if (CurrentSpeeds != null)
                    height -= StandardSpacing +
                        EditorGUI.GetPropertyHeight(CurrentSpeeds, label);

                if (CurrentSynchronizeChildren != null)
                    height -= StandardSpacing +
                        EditorGUI.GetPropertyHeight(CurrentSynchronizeChildren, label);
            }

            return height;
        }

        /************************************************************************************************************************/

        private SerializedProperty _RootProperty;
        private ReorderableList _CurrentChildList;

        /// <inheritdoc/>
        public override void OnGUI(Rect area, SerializedProperty property, GUIContent label)
        {
            _RootProperty = null;

            base.OnGUI(area, property, label);

            if (_RootProperty == null ||
                !_RootProperty.isExpanded)
                return;

            using (new DrawerContext(_RootProperty))
            {
                if (Context.Transition == null)
                    return;

                _CurrentChildList = GatherDetails(_RootProperty);
                if (_CurrentChildList == null)
                    return;

                var indentLevel = EditorGUI.indentLevel;

                area.yMin = area.yMax - _CurrentChildList.GetHeight();

                EditorGUI.indentLevel++;
                area = EditorGUI.IndentedRect(area);

                EditorGUI.indentLevel = 0;
                _CurrentChildList.DoList(area);

                EditorGUI.indentLevel = indentLevel;

                TryCollapseArrays();
            }
        }

        /************************************************************************************************************************/

        /// <inheritdoc/>
        protected override void DoChildPropertyGUI(
            ref Rect area,
            SerializedProperty rootProperty,
            SerializedProperty property,
            GUIContent label)
        {
            if (Context.Transition != null)
            {
                area.height = 0;

                // If we find the Animations property, hide it to draw it last.

                var path = property.propertyPath;
                if (path.EndsWith("." + ManualMixerTransition.AnimationsField))
                {
                    _RootProperty = rootProperty;
                    return;
                }
                else if (_RootProperty != null)
                {
                    // If we already found the Animations property, also hide Speeds and Synchronize Children.
                    if (path.EndsWith("." + ManualMixerTransition.SpeedsField) ||
                        path.EndsWith("." + ManualMixerTransition.SynchronizeChildrenField))
                        return;
                }
            }

            base.DoChildPropertyGUI(ref area, rootProperty, property, label);
        }

        /************************************************************************************************************************/

        private static float _SpeedLabelWidth;
        private static float _SyncLabelWidth;

        /// <summary>Splits the specified `area` into separate sections.</summary>
        protected static void SplitListRect(Rect area, bool isHeader,
            out Rect animation, out Rect speed, out Rect sync)
        {
            if (_SpeedLabelWidth == 0)
                _SpeedLabelWidth = AnimancerGUI.CalculateWidth(EditorStyles.popup, "Speed");

            if (_SyncLabelWidth == 0)
                _SyncLabelWidth = AnimancerGUI.CalculateWidth(EditorStyles.popup, "Sync");

            var spacing = StandardSpacing;

            var syncWidth = isHeader ?
                _SyncLabelWidth :
                ToggleWidth - spacing;

            var speedWidth = _SpeedLabelWidth + _SyncLabelWidth - syncWidth;
            if (!isHeader)
            {
                // Don't use Clamp because the max might be smaller than the min.
                var max = Math.Max(area.height, area.width * 0.25f - 30);
                speedWidth = Math.Min(speedWidth, max);
            }

            area.width += spacing;
            if (TwoLineMode && !isHeader)
            {
                animation = area;
                area.y += area.height;
                sync = StealFromRight(ref area, syncWidth, spacing);
                speed = area;
            }
            else
            {
                sync = StealFromRight(ref area, syncWidth, spacing);
                speed = StealFromRight(ref area, speedWidth, spacing);
                animation = area;
            }
        }

        /************************************************************************************************************************/
        #region Headers
        /************************************************************************************************************************/

        /// <summary>Draws the headdings of the child list.</summary>
        protected virtual void DoChildListHeaderGUI(Rect area)
        {
            SplitListRect(area, true, out var animationArea, out var speedArea, out var syncArea);

            DoAnimationHeaderGUI(animationArea);
            DoSpeedHeaderGUI(speedArea);
            DoSyncHeaderGUI(syncArea);
        }

        /************************************************************************************************************************/

        /// <summary>Draws an "Animation" header.</summary>
        protected void DoAnimationHeaderGUI(Rect area)
        {
            using (var label = PooledGUIContent.Acquire("Animation",
                $"The animations that will be used for each child state" +
                $"\n\nCtrl + Click to allow picking Transition Assets" +
                $" (or anything that implements {nameof(ITransition)})"))
            {
                DoHeaderDropdownGUI(area, CurrentAnimations, label, menu =>
                {
                    menu.AddItem(new(TwoLineMode.MenuItem), TwoLineMode.Value, () =>
                    {
                        TwoLineMode.Value = !TwoLineMode.Value;
                        ReSelectCurrentObjects();
                    });
                });
            }
        }

        /************************************************************************************************************************/
        #region Speeds
        /************************************************************************************************************************/

        /// <summary>Draws a "Speed" header.</summary>
        protected void DoSpeedHeaderGUI(Rect area)
        {
            using (var label = PooledGUIContent.Acquire("Speed", Strings.Tooltips.Speed))
            {
                DoHeaderDropdownGUI(area, CurrentSpeeds, label, menu =>
                {
                    AddPropertyModifierFunction(menu, "Reset All to 1",
                        CurrentSpeeds.arraySize == 0 ? MenuFunctionState.Selected : MenuFunctionState.Normal,
                        (_) => CurrentSpeeds.arraySize = 0);

                    AddPropertyModifierFunction(menu, "Normalize Durations", MenuFunctionState.Normal, NormalizeDurations);
                });
            }
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Recalculates the <see cref="CurrentSpeeds"/> depending on the <see cref="AnimationClip.length"/> of
        /// their animations so that they all take the same amount of time to play fully.
        /// </summary>
        private static void NormalizeDurations(SerializedProperty property)
        {
            var speedCount = CurrentSpeeds.arraySize;

            var lengths = new float[CurrentAnimations.arraySize];
            if (lengths.Length <= 1)
                return;

            int nonZeroLengths = 0;
            float totalLength = 0;
            float totalSpeed = 0;
            for (int i = 0; i < lengths.Length; i++)
            {
                var state = CurrentAnimations.GetArrayElementAtIndex(i).objectReferenceValue;
                if (AnimancerUtilities.TryGetLength(state, out var length) &&
                    length > 0)
                {
                    nonZeroLengths++;
                    totalLength += length;
                    lengths[i] = length;

                    if (speedCount > 0)
                        totalSpeed += CurrentSpeeds.GetArrayElementAtIndex(i).floatValue;
                }
            }

            if (nonZeroLengths == 0)
                return;

            var averageLength = totalLength / nonZeroLengths;
            var averageSpeed = speedCount > 0 ? totalSpeed / nonZeroLengths : 1;

            CurrentSpeeds.arraySize = lengths.Length;
            InitializeSpeeds(speedCount);

            for (int i = 0; i < lengths.Length; i++)
            {
                if (lengths[i] == 0)
                    continue;

                CurrentSpeeds.GetArrayElementAtIndex(i).floatValue = averageSpeed * lengths[i] / averageLength;
            }

            TryCollapseArrays();
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Initializes every element in the <see cref="CurrentSpeeds"/> array
        /// from the `start` to the end of the array to contain a value of 1.
        /// </summary>
        public static void InitializeSpeeds(int start)
        {
            var count = CurrentSpeeds.arraySize;
            while (start < count)
                CurrentSpeeds.GetArrayElementAtIndex(start++).floatValue = 1;
        }

        /************************************************************************************************************************/
        #endregion
        /************************************************************************************************************************/
        #region Sync
        /************************************************************************************************************************/

        /// <summary>Draws a "Sync" header.</summary>
        protected void DoSyncHeaderGUI(Rect area)
        {
            using (var label = PooledGUIContent.Acquire("Sync",
                "Determines which child states have their normalized times constantly synchronized"))
            {
                DoHeaderDropdownGUI(area, CurrentSpeeds, label, menu =>
                {
                    var syncCount = CurrentSynchronizeChildren.arraySize;

                    var allState = syncCount == 0 ? MenuFunctionState.Selected : MenuFunctionState.Normal;
                    AddPropertyModifierFunction(menu, "All", allState,
                        (_) => CurrentSynchronizeChildren.arraySize = 0);

                    var syncNone = syncCount == CurrentAnimations.arraySize;
                    if (syncNone)
                    {
                        for (int i = 0; i < syncCount; i++)
                        {
                            if (CurrentSynchronizeChildren.GetArrayElementAtIndex(i).boolValue)
                            {
                                syncNone = false;
                                break;
                            }
                        }
                    }
                    var noneState = syncNone ? MenuFunctionState.Selected : MenuFunctionState.Normal;
                    AddPropertyModifierFunction(menu, "None", noneState, (_) =>
                    {
                        var count = CurrentSynchronizeChildren.arraySize = CurrentAnimations.arraySize;
                        for (int i = 0; i < count; i++)
                            CurrentSynchronizeChildren.GetArrayElementAtIndex(i).boolValue = false;
                    });

                    AddPropertyModifierFunction(menu, "Invert", MenuFunctionState.Normal, (_) =>
                    {
                        var count = CurrentSynchronizeChildren.arraySize;
                        for (int i = 0; i < count; i++)
                        {
                            var property = CurrentSynchronizeChildren.GetArrayElementAtIndex(i);
                            property.boolValue = !property.boolValue;
                        }

                        var newCount = CurrentSynchronizeChildren.arraySize = CurrentAnimations.arraySize;
                        for (int i = count; i < newCount; i++)
                            CurrentSynchronizeChildren.GetArrayElementAtIndex(i).boolValue = false;
                    });

                    AddPropertyModifierFunction(menu, "Non-Stationary", MenuFunctionState.Normal, (_) =>
                    {
                        var count = CurrentAnimations.arraySize;

                        for (int i = 0; i < count; i++)
                        {
                            var state = CurrentAnimations.GetArrayElementAtIndex(i).objectReferenceValue;
                            if (state == null)
                                continue;

                            if (i >= syncCount)
                            {
                                CurrentSynchronizeChildren.arraySize = i + 1;
                                for (int j = syncCount; j < i; j++)
                                    CurrentSynchronizeChildren.GetArrayElementAtIndex(j).boolValue = true;
                                syncCount = i + 1;
                            }

                            CurrentSynchronizeChildren.GetArrayElementAtIndex(i).boolValue =
                                AnimancerUtilities.TryGetAverageVelocity(state, out var velocity) &&
                                velocity != default;
                        }

                        TryCollapseSync();
                    });
                });
            }
        }

        /************************************************************************************************************************/

        private static void SyncNone()
        {
            var count = CurrentSynchronizeChildren.arraySize = CurrentAnimations.arraySize;
            for (int i = 0; i < count; i++)
                CurrentSynchronizeChildren.GetArrayElementAtIndex(i).boolValue = false;
        }

        /************************************************************************************************************************/
        #endregion
        /************************************************************************************************************************/

        /// <summary>Draws the GUI for a header dropdown button.</summary>
        public static void DoHeaderDropdownGUI(
            Rect area,
            SerializedProperty property,
            GUIContent content,
            Action<GenericMenu> populateMenu)
        {
            if (property != null)
                EditorGUI.BeginProperty(area, GUIContent.none, property);

            if (populateMenu != null)
            {
                if (EditorGUI.DropdownButton(area, content, FocusType.Passive))
                {
                    var menu = new GenericMenu();
                    populateMenu(menu);
                    menu.ShowAsContext();
                }
            }
            else
            {
                GUI.Label(area, content);
            }

            if (property != null)
                EditorGUI.EndProperty();
        }

        /************************************************************************************************************************/

        /// <summary>Draws the footer of the child list.</summary>
        protected virtual void DoChildListFooterGUI(Rect area)
        {
            ReorderableList.defaultBehaviours.DrawFooter(area, _CurrentChildList);

            EditorGUI.BeginChangeCheck();

            area.xMax = EditorGUIUtility.labelWidth + IndentSize;

            area.y++;
            area.height = LineHeight;

            using (var label = PooledGUIContent.Acquire("Count"))
            {
                var indentLevel = EditorGUI.indentLevel;
                EditorGUI.indentLevel = 0;

                var labelWidth = EditorGUIUtility.labelWidth;
                EditorGUIUtility.labelWidth = CalculateLabelWidth(label.text);

                var count = EditorGUI.DelayedIntField(area, label, _CurrentChildList.count);

                if (EditorGUI.EndChangeCheck())
                    ResizeList(count);

                EditorGUIUtility.labelWidth = labelWidth;

                EditorGUI.indentLevel = indentLevel;
            }
        }

        /************************************************************************************************************************/
        #endregion
        /************************************************************************************************************************/

        /// <summary>Calculates the height of the state at the specified `index`.</summary>
        protected virtual float GetElementHeight(int index)
            => TwoLineMode
            ? LineHeight * 2
            : LineHeight;

        /************************************************************************************************************************/

        /// <summary>Draws the GUI of the state at the specified `index`.</summary>
        private void DoElementGUI(Rect area, int index, bool isActive, bool isFocused)
        {
            if (index < 0 || index > CurrentAnimations.arraySize)
                return;

            area.height = LineHeight;

            var state = CurrentAnimations.GetArrayElementAtIndex(index);
            var speed = CurrentSpeeds.arraySize > 0
                ? CurrentSpeeds.GetArrayElementAtIndex(index)
                : null;
            DoElementGUI(area, index, state, speed);
        }

        /************************************************************************************************************************/

        /// <summary>Draws the GUI of the animation at the specified `index`.</summary>
        protected virtual void DoElementGUI(Rect area, int index,
            SerializedProperty animation, SerializedProperty speed)
        {
            SplitListRect(area, false, out var animationArea, out var speedArea, out var syncArea);

            DoAnimationField(animationArea, animation);
            DoSpeedFieldGUI(speedArea, speed, index);
            DoSyncToggleGUI(syncArea, index);
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Draws an <see cref="EditorGUI.ObjectField(Rect, GUIContent, Object, Type, bool)"/> that accepts
        /// <see cref="AnimationClip"/>s and <see cref="ITransition"/>s
        /// </summary>
        public static void DoAnimationField(Rect area, SerializedProperty property)
        {
            EditorGUI.BeginProperty(area, GUIContent.none, property);

            var targetObject = property.serializedObject.targetObject;
            var oldReference = property.objectReferenceValue;

            var currentEvent = Event.current;
            var isDrag =
                currentEvent.type == EventType.DragUpdated ||
                currentEvent.type == EventType.DragPerform;
            var type =
                isDrag ||
                currentEvent.control ||
                currentEvent.commandName == "ObjectSelectorUpdated"
                ? typeof(Object)
                : typeof(AnimationClip);

            var allowSceneObjects = targetObject != null && !EditorUtility.IsPersistent(targetObject);

            EditorGUI.BeginChangeCheck();

            var newReference = EditorGUI.ObjectField(
                area,
                GUIContent.none,
                oldReference,
                type,
                allowSceneObjects);

            if (EditorGUI.EndChangeCheck())
            {
                if (newReference == null ||
                    (IsClipOrTransition(newReference) && newReference != targetObject))
                    property.objectReferenceValue = newReference;
            }

            if (isDrag && area.Contains(currentEvent.mousePosition))
            {
                var objects = DragAndDrop.objectReferences;
                if (objects.Length != 1 ||
                    !IsClipOrTransition(objects[0]) ||
                    objects[0] == targetObject)
                    DragAndDrop.visualMode = DragAndDropVisualMode.Rejected;
            }

            EditorGUI.EndProperty();
        }

        /// <summary>Is the `clipOrTransition` an <see cref="AnimationClip"/> or <see cref="ITransition"/>?</summary>
        public static bool IsClipOrTransition(object clipOrTransition)
            => clipOrTransition is AnimationClip || clipOrTransition is ITransition;

        /************************************************************************************************************************/

        private static CompactUnitConversionCache _XSuffixCache;

        /// <summary>
        /// Draws a toggle to enable or disable <see cref="ManualMixerState.SynchronizedChildren"/> for the child
        /// at the specified `index`.
        /// </summary>
        protected void DoSpeedFieldGUI(Rect area, SerializedProperty speed, int index)
        {
            if (speed != null)
            {
                EditorGUI.PropertyField(area, speed, GUIContent.none);
            }
            else// If this element doesn't have its own speed property, just show 1.
            {
                EditorGUI.BeginProperty(area, GUIContent.none, CurrentSpeeds);

                _XSuffixCache ??= new("x");

                var value = UnitsAttributeDrawer.DoSpecialFloatField(
                    area,
                    null,
                    1,
                    _XSuffixCache);

                // Middle Click toggles from 1 to -1.
                if (TryUseClickEvent(area, 2))
                    value = -1;

                if (value != 1)
                {
                    CurrentSpeeds.InsertArrayElementAtIndex(0);
                    CurrentSpeeds.GetArrayElementAtIndex(0).floatValue = 1;
                    CurrentSpeeds.arraySize = CurrentAnimations.arraySize;
                    CurrentSpeeds.GetArrayElementAtIndex(index).floatValue = value;
                }

                EditorGUI.EndProperty();
            }
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Draws a toggle to enable or disable <see cref="ManualMixerState.SynchronizedChildren"/>
        /// for the child at the specified `index`.
        /// </summary>
        protected void DoSyncToggleGUI(Rect area, int index)
        {
            var syncProperty = CurrentSynchronizeChildren;
            var syncFlagCount = syncProperty.arraySize;

            var enabled = true;

            if (index < syncFlagCount)
            {
                syncProperty = syncProperty.GetArrayElementAtIndex(index);
                enabled = syncProperty.boolValue;
            }

            EditorGUI.BeginChangeCheck();
            EditorGUI.BeginProperty(area, GUIContent.none, syncProperty);

            enabled = GUI.Toggle(area, enabled, GUIContent.none);

            EditorGUI.EndProperty();
            if (EditorGUI.EndChangeCheck())
            {
                if (index < syncFlagCount)
                {
                    syncProperty.boolValue = enabled;
                }
                else
                {
                    syncProperty.arraySize = index + 1;

                    for (int i = syncFlagCount; i < index; i++)
                    {
                        syncProperty.GetArrayElementAtIndex(i).boolValue = true;
                    }

                    syncProperty.GetArrayElementAtIndex(index).boolValue = enabled;
                }
            }
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Called when adding a new state to the list to ensure that
        /// any other relevant arrays have new elements added as well.
        /// </summary>
        private void OnAddElement(ReorderableList list)
        {
            var index = list.index;
            if (index < 0 || Event.current.button == 1)// Right Click to add at the end.
            {
                index = CurrentAnimations.arraySize - 1;
                if (index < 0)
                    index = 0;
            }

            OnAddElement(index);
        }

        /// <summary>
        /// Called when adding a new state to the list to ensure that
        /// any other relevant arrays have new elements added as well.
        /// </summary>
        protected virtual void OnAddElement(int index)
        {
            CurrentAnimations.InsertArrayElementAtIndex(index);

            if (CurrentSpeeds.arraySize > 0)
                CurrentSpeeds.InsertArrayElementAtIndex(index);

            if (CurrentSynchronizeChildren.arraySize > index)
                CurrentSynchronizeChildren.InsertArrayElementAtIndex(index);
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Called when removing a state from the list to ensure that
        /// any other relevant arrays have elements removed as well.
        /// </summary>
        protected virtual void OnRemoveElement(ReorderableList list)
        {
            var index = list.index;

            Serialization.RemoveArrayElement(CurrentAnimations, index);

            if (CurrentSpeeds.arraySize > index)
                Serialization.RemoveArrayElement(CurrentSpeeds, index);

            if (CurrentSynchronizeChildren.arraySize > index)
                Serialization.RemoveArrayElement(CurrentSynchronizeChildren, index);
        }

        /************************************************************************************************************************/

        /// <summary>Sets the number of items in the child list.</summary>
        protected virtual void ResizeList(int size)
        {
            CurrentAnimations.arraySize = size;

            if (CurrentSpeeds.arraySize > size)
                CurrentSpeeds.arraySize = size;

            if (CurrentSynchronizeChildren.arraySize > size)
                CurrentSynchronizeChildren.arraySize = size;
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Called when reordering states in the list to ensure that
        /// any other relevant arrays have their corresponding elements reordered as well.
        /// </summary>
        protected virtual void OnReorderList(ReorderableList list, int oldIndex, int newIndex)
        {
            CurrentSpeeds.MoveArrayElement(oldIndex, newIndex);

            var syncCount = CurrentSynchronizeChildren.arraySize;
            if (Math.Max(oldIndex, newIndex) >= syncCount)
            {
                CurrentSynchronizeChildren.arraySize++;
                CurrentSynchronizeChildren.GetArrayElementAtIndex(syncCount).boolValue = true;
                CurrentSynchronizeChildren.arraySize = newIndex + 1;
            }

            CurrentSynchronizeChildren.MoveArrayElement(oldIndex, newIndex);
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Calls <see cref="TryCollapseSpeeds"/> and <see cref="TryCollapseSync"/>.
        /// </summary>
        public static void TryCollapseArrays()
        {
            if (CurrentProperty == null ||
                CurrentProperty.hasMultipleDifferentValues)
                return;

            TryCollapseSpeeds();
            TryCollapseSync();
        }

        /************************************************************************************************************************/

        /// <summary>
        /// If every element in the <see cref="CurrentSpeeds"/> array is 1,
        /// this method sets the array size to 0.
        /// </summary>
        public static void TryCollapseSpeeds()
        {
            var property = CurrentSpeeds;
            if (property == null)
                return;

            var speedCount = property.arraySize;
            if (speedCount <= 0)
                return;

            for (int i = 0; i < speedCount; i++)
            {
                if (property.GetArrayElementAtIndex(i).floatValue != 1)
                    return;
            }

            property.arraySize = 0;
        }

        /************************************************************************************************************************/

        /// <summary>
        /// Removes any true elements from the end of the <see cref="CurrentSynchronizeChildren"/> array.
        /// </summary>
        public static void TryCollapseSync()
        {
            var property = CurrentSynchronizeChildren;
            if (property == null)
                return;

            var count = property.arraySize;
            var changed = false;

            for (int i = count - 1; i >= 0; i--)
            {
                if (property.GetArrayElementAtIndex(i).boolValue)
                {
                    count = i;
                    changed = true;
                }
                else
                {
                    break;
                }
            }

            if (changed)
                property.arraySize = count;
        }

        /************************************************************************************************************************/
    }
}

#endif