【Unity】【CustomPropertyDrawer】Inspector の Color フィールドを拡張する

using UnityEditor;
using UnityEngine;
 
[CustomPropertyDrawer(typeof(Color))]
public class ColorPropertyDrawer : PropertyDrawer
{
    private const int ColorMax = 4;
    private SerializedProperty[] _rgba;
    private Color _color = new Color();
    private bool _isCached;
    private string _colorStr;
    private static readonly string[] Labels = {
        "Red", "Green", "Blue", "Alpha"
    };
 
    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
    {
        if (!_isCached)
        {
            _rgba = new SerializedProperty[ColorMax];
            _rgba[0] = property.FindPropertyRelative("r");
            _rgba[1] = property.FindPropertyRelative("g");
            _rgba[2] = property.FindPropertyRelative("b");
            _rgba[3] = property.FindPropertyRelative("a");
            _isCached = true;
        }
 
        position.height = EditorGUIUtility.singleLineHeight;
        
        using (var check = new EditorGUI.ChangeCheckScope())
        {
            for (var i = 0; i < ColorMax; i++)
                _color[i] = _rgba[i].floatValue;
            
            _color = EditorGUI.ColorField(position, label, _color);
            
            if (check.changed)
                for (var i = 0; i < ColorMax; i++)
                    _rgba[i].floatValue = _color[i];
        }
 
        property.isExpanded = EditorGUI.Foldout(position, property.isExpanded, GUIContent.none);
        if (!property.isExpanded)
            return;
 
        using (new EditorGUI.IndentLevelScope(1))
        {
            using (var check = new EditorGUI.ChangeCheckScope())
            {
                for (var i = 0; i < ColorMax; i++)
                {
                    position.y += EditorGUIUtility.singleLineHeight;
                    _color[i] = _rgba[i].floatValue;
                    _color[i] = EditorGUI.Slider(position, Labels[i], _color[i], 0f, 1f);
                }
                if (check.changed)
                    for (var i = 0; i < ColorMax; i++)
                        _rgba[i].floatValue = _color[i];
            }
 
            position.y += EditorGUIUtility.singleLineHeight;
            using (var check = new EditorGUI.ChangeCheckScope())
            {
                for (var i = 0; i < ColorMax; i++)
                    _color[i] = _rgba[i].floatValue;
                
                _colorStr = EditorGUI.DelayedTextField(position, "HTML Color Code", ColorUtility.ToHtmlStringRGB(_color));
                if (check.changed)
                    if (ColorUtility.TryParseHtmlString("#" + _colorStr, out var color))
                        for (var i = 0; i < ColorMax - 1; i++)
                            _rgba[i].floatValue = color[i];
            }
        }
    }
 
    public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
    {
        if (!property.isExpanded)
            return EditorGUIUtility.singleLineHeight;
        
        return EditorGUIUtility.singleLineHeight * 6;
    }
}