fix stencil pass

Assets/Portal/Runtime/Portal.cs

@@ -4,6 +4,7 @@ using EscapeRoomEngine.Engine.Runtime.Modules;
 using EscapeRoomEngine.Engine.Runtime.Utilities;
 using NaughtyAttributes;
 using UnityEngine;
+using UnityEngine.Serialization;
 
 namespace EscapeRoomEngine.Portal.Runtime
 {
@@ -12,9 +13,10 @@ namespace EscapeRoomEngine.Portal.Runtime
     /// </summary>
     public class Portal : DoorState
     {
+        private static readonly int PortalNumberProperty = Shader.PropertyToID("_PortalNumber");
         public static readonly Matrix4x4 HalfRotation = Matrix4x4.Rotate(Quaternion.Euler(0, 180, 0));
 
-        private static int _portalCounter;
+        private static int _portalCounter = 1;
         
         /// <summary>
         /// The portal that is connected with this one.
@@ -40,6 +42,7 @@ namespace EscapeRoomEngine.Portal.Runtime
         protected virtual void Awake()
         {
             PortalNumber = _portalCounter++;
+            screen.material.SetInt(PortalNumberProperty, PortalNumber);
             
             DoorEvent += (_, type) =>
             {