SubsceneReference

using System;
using UnityEngine;
using Hash128 = Unity.Entities.Hash128;

#if UNITY_EDITOR
using UnityEditor;

[CustomPropertyDrawer( typeof( SubSceneReference ) )]
public class SubSceneReferencePropertyDrawer : PropertyDrawer
{
    public override void OnGUI( Rect position, SerializedProperty property, GUIContent label )
    {
        EditorGUI.BeginProperty( position, GUIContent.none, property );

        var sceneObject = property.FindPropertyRelative( "sceneAsset" ).objectReferenceValue;

        {
            //Draw scene asset
            var sceneAsset = property.FindPropertyRelative( "sceneAsset" );
            position = EditorGUI.PrefixLabel( position, GUIUtility.GetControlID( FocusType.Passive ), label );

            if ( sceneAsset != null )
            {
                sceneAsset.objectReferenceValue = EditorGUI.ObjectField( position, sceneAsset.objectReferenceValue,
                typeof( SceneAsset ), false );
            }
        }

        var sceneHash = property.FindPropertyRelative( "SceneReference" );

        var hash = default( Hash128 );

        if ( sceneObject != null )
        {
            var sceneGuid = new GUID( AssetDatabase.AssetPathToGUID( AssetDatabase.GetAssetPath( sceneObject ) ) );

            hash = sceneGuid;
        }

        var value = sceneHash.FindPropertyRelative( "Value" );

        if ( value == null ) throw new Exception( "Failed to retrieve value property from SubSceneReference" );

        value.FindPropertyRelative( "x" ).longValue = ( long ) hash.Value.x;
        value.FindPropertyRelative( "y" ).longValue = ( long ) hash.Value.y;
        value.FindPropertyRelative( "z" ).longValue = ( long ) hash.Value.z;
        value.FindPropertyRelative( "w" ).longValue = ( long ) hash.Value.w;

        EditorGUI.EndProperty( );
    }
}
#endif

[Serializable]
public class SubSceneReference
{
    public static implicit operator Hash128( SubSceneReference reference ) => reference.SceneReference;

#if UNITY_EDITOR
    [SerializeField]
    SceneAsset sceneAsset;
#endif


    public Hash128 SceneReference;
}