Expose sorting layer in MeshRenderer inspector, for rendering on top of sprites

MeshRendererSortingEditor.cs

using System;
using UnityEngine;
using UnityEditor;
using System.Linq;
using System.Reflection;

/// This just exposes the Sorting Layer / Order in MeshRenderer since it's there
/// but not displayed in the inspector. Getting MeshRenderer to render in front
/// of a SpriteRenderer is pretty hard without this.
/// Adapted from https://gist.github.com/sinbad/bd0c49bc462289fa1a018ffd70d806e3
/// With changes from https://forum.unity.com/threads/extending-mesh-renderer-component-with-a-custom-editor.949176/
/// to preserve the Unity MeshRenderer GUI. 
[CustomEditor(typeof(MeshRenderer))]
[CanEditMultipleObjects]
public class MeshRendererSortingEditor : Editor
{
    private Editor defaultEditor;
    private MeshRenderer meshRenderer;
    private static bool showSorting = true;
    private string header = "2D Sorting";

    private SerializedProperty sortingLayerIdProperty;
    private SerializedProperty sortingOrderProperty;

    [InitializeOnLoadMethod]
    private static void OnLoad()
    {
        showSorting = EditorPrefs.GetBool("MeshRendererSortingEditor.showSorting");
    }

    private void OnEnable()
    {
        defaultEditor = CreateEditor(targets, Type.GetType("UnityEditor.MeshRendererEditor, UnityEditor"));
        meshRenderer = target as MeshRenderer;

        sortingLayerIdProperty = serializedObject.FindProperty("m_SortingLayerID");
        sortingOrderProperty = serializedObject.FindProperty("m_SortingOrder");
    }

    private void OnDisable()
    {
        //When OnDisable is called, the default editor we created should be destroyed to avoid memory leakage.
        //Also, make sure to call any required methods like OnDisable
        var disableMethod = defaultEditor.GetType().GetMethod("OnDisable", BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
        if (disableMethod != null)
            disableMethod.Invoke(defaultEditor, null);
        DestroyImmediate(defaultEditor);
    }

    public override void OnInspectorGUI()
    {
        defaultEditor.OnInspectorGUI();

        serializedObject.Update();

        EditorGUI.BeginChangeCheck();
        showSorting = EditorGUILayout.BeginFoldoutHeaderGroup(showSorting, header);
        if (EditorGUI.EndChangeCheck())
            EditorPrefs.SetBool("MeshRendererSortingEditor.showSorting", showSorting);

        if (showSorting)
        {
            EditorGUI.indentLevel++;

            var rect = EditorGUILayout.GetControlRect();
            EditorGUI.BeginProperty(rect, new GUIContent("Sorting Layer"), sortingLayerIdProperty);
            EditorGUI.BeginChangeCheck();
            var newId = DrawSortingLayersPopup(rect, meshRenderer.sortingLayerID);
            if (EditorGUI.EndChangeCheck())
                sortingLayerIdProperty.intValue = newId;
            EditorGUI.EndProperty();

            EditorGUILayout.PropertyField(sortingOrderProperty);

            EditorGUI.indentLevel--;
        }

        EditorGUILayout.EndFoldoutHeaderGroup();

        serializedObject.ApplyModifiedProperties();
    }

    private static int DrawSortingLayersPopup(Rect rect, int layerID)
    {
        var layers = SortingLayer.layers;
        var names = layers.Select(l => l.name).ToArray();

        if (!SortingLayer.IsValid(layerID))
            layerID = SortingLayer.NameToID("Default");

        var index = 0;
        for (int i = 0; i < layers.Length; i++) //No IndexOf in LINQ unfortunately
            if (layers[i].id == layerID)
                index = i;

        index = EditorGUI.Popup(rect, "Sorting Layer", index, names);

        return layers[index].id;
    }
}

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