PhysicsCategoryMask.cs

using System;
using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using Unity.Physics.Authoring;
#if UNITY_EDITOR
using UnityEditor;
#endif

[Serializable]
public struct PhysicsCategoryMask
{
    public uint Value;

    public static implicit operator uint(PhysicsCategoryMask mask) => mask.Value;
}

#if UNITY_EDITOR
[CustomPropertyDrawer(typeof(PhysicsCategoryMask))]
public class PhysicsCategoryMaskDrawer : PropertyDrawer
{
    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
    {
        var assets = GetAssets<PhysicsCategoryNames>();
        var asset = assets.First();
        var names = asset.CategoryNames.Where(name => !string.IsNullOrEmpty(name)).ToArray();

        label = EditorGUI.BeginProperty(position, label, property);
        var controlPosition = EditorGUI.PrefixLabel(position, label);

        EditorGUI.indentLevel = 0;

        var valueProperty = property.FindPropertyRelative(nameof(PhysicsCategoryMask.Value));
        if (valueProperty == null)
            throw new InvalidOperationException();

        var value = valueProperty.intValue;

        // MaskField wants 'Everything' represented as -1,
        if (IsEverythingSet(value, names.Length))
        {
            value = ~0;
        }

        EditorGUI.BeginChangeCheck();
        var maskField = EditorGUI.MaskField(controlPosition, GUIContent.none, value, names);
        if (EditorGUI.EndChangeCheck())
        {
            if (maskField == -1)
            {
                // Calculate the cumulative value.
                var everything = 0;
                for (int i = 0, count = names.Length; i < count; ++i)
                {
                    everything |= 1 << i;
                }
                maskField = everything;
            }
            valueProperty.intValue = maskField;
        }
        EditorGUI.EndProperty();
    }

    public static List<T> GetAssets<T>() where T : ScriptableObject
    {
        return AssetDatabase.FindAssets($"t:{typeof(T).Name}")
            .Select(AssetDatabase.GUIDToAssetPath)
            .Select(AssetDatabase.LoadAssetAtPath<T>)
            .Where(c => c != null).ToList();
    }

    public static bool IsEverythingSet(int maskValue, int length)
    {
        var value = 0;
        var everything = 0;
        for (int i = 1, count = length; i < count; ++i)
        {
            var isSelected = (maskValue & (1 << i)) != 0;
            value |= isSelected ? 1 << i : 0;
            everything |= 1 << i;
        }
        return value == everything;
    }

}
#endif