Custom material editor

using UnityEngine;
using UnityEditor;

[CanEditMultipleObjects]
[CustomEditor(typeof(Material), true)]
public class CustomMaterialEditor : MaterialEditor
{
    string[] mRenderQueueNames = new string[]
    {
        "Set in shader",
        "Background",
        "Geometry",
        "AlphaTest",
        "Transparent",
        "Overlay",
    };

    int[] mRenderQueueValues = new int[]
    {
        -1,
        1000,
        2000,
        2450,
        3000,
        4000,
    };

    int GetClosest (int val)
    {
        int minDist = int.MaxValue;
        int minVal = 0;

        for (int i = 0; i < mRenderQueueValues.Length; ++i)
        {
            int dist = Mathf.Abs(val - mRenderQueueValues[i]);

            if (dist < minDist)
            {
                minDist = dist;
                minVal = i;
            }
        }
        return minVal;
    }

    public override void OnInspectorGUI ()
    {
        EditorGUIUtility.labelWidth = 80;
        serializedObject.Update();

        if (serializedObject.isEditingMultipleObjects)
        {
            serializedObject.DrawProperty("m_CustomRenderQueue", "Render Q");
        }
        else
        {
            var prop = serializedObject.FindProperty("m_CustomRenderQueue");
            int closestQueue = GetClosest(prop.intValue);
            int offset = prop.intValue - mRenderQueueValues[closestQueue];

            GUI.changed = false;

            GUILayout.BeginHorizontal();
            int desiredQueue = EditorGUILayout.Popup("Render Q", closestQueue, mRenderQueueNames);
            if (desiredQueue == 0) offset = 0;
            EditorGUILayout.LabelField("+", GUILayout.Width(14f));

            EditorGUI.BeginDisabledGroup(desiredQueue == 0);
            offset = EditorGUILayout.IntField(offset, GUILayout.Width(64f));
            EditorGUI.EndDisabledGroup();
            GUILayout.EndHorizontal();

            if (GUI.changed) prop.intValue = mRenderQueueValues[desiredQueue] + offset;
        }

        serializedObject.ApplyModifiedProperties();
        base.OnInspectorGUI();
    }
}