Moved user32Dll Imports to seperate File.

Added Z-Order.

OBSBlur/Window/WindowManager.cs

@@ -1,12 +1,13 @@
 using System.Diagnostics;
-using System.Runtime.InteropServices;
-using System.Text;
 
 namespace OBSBlur.Window;
 
-public class WindowManager : IDisposable
+public partial class WindowManager : IDisposable
 {
-    public readonly HashSet<WindowInfo> Windows = new(1024);
+    private readonly HashSet<WindowInfo> _windows = new(1024);
+    private List<IntPtr> _zOrder = GetWindowZOrder();
+    public IntPtr[] WindowZOrder => _zOrder.ToArray();
+    public WindowInfo[] WindowInfos => _windows.ToArray();
     public int UpdateInterval = 10;
     private bool _keepUpdating = true;
     public WindowManager()
@@ -15,14 +16,46 @@ public class WindowManager : IDisposable
         {
             while (_keepUpdating)
             {
-                Windows.Clear();
+                WindowInfo[] windowInfoBefore = WindowInfos;
+                IntPtr[] zOrderBefore = WindowZOrder;
+                _windows.Clear();
                 EnumWindows(GetWindowInfo, 0);
+                _zOrder = GetWindowZOrder();
+                
+                WindowsUpdated?.Invoke(WindowInfos);
+                WindowInfo[] changedWindows = WindowInfos.Where(info => !windowInfoBefore.Contains(info)).ToArray();
+                if(changedWindows.Length > 0)
+                    WindowsChanged?.Invoke(windowInfoBefore.Where(b => changedWindows.Select(c => c.WindowHandle).Contains(b.WindowHandle)).ToArray(), changedWindows);
+                if (zOrderBefore.Length != WindowZOrder.Length)
+                    WindowZOrderChanged?.Invoke(WindowZOrder);
+                else
+                {
+                    IntPtr[] zOrderAfter = WindowZOrder;
+                    for(int i = 0; i < zOrderBefore.Length; i++)
+                        if (!zOrderBefore[i].Equals(zOrderAfter[i]))
+                        {
+                            WindowZOrderChanged?.Invoke(zOrderAfter);
+                            break;
                         }
+                            
+                }
+                
                 Thread.Sleep(UpdateInterval);
+            }
         });
         t.Start();
     }
 
+    public delegate void WindowsUpdatedHandler(WindowInfo[] windowInfos);
+    public event WindowsUpdatedHandler WindowsUpdated;
+
+    public delegate void WindowsChangedHandler(WindowInfo[] before, WindowInfo[] after);
+    public event WindowsChangedHandler WindowsChanged;
+
+    public delegate void WindowZOrderChangedHandler(IntPtr[] newOrder);
+
+    public event WindowZOrderChangedHandler WindowZOrderChanged;
+
     private bool GetWindowInfo(IntPtr windowHandle, IntPtr lParam)
     {
         WindowPlacement windowPlacement = new ();
@@ -43,38 +76,11 @@ public class WindowManager : IDisposable
         if (windowTitle.Length < 1)
             return true;
 
-        Windows.Add(new WindowInfo(windowHandle, windowTitle, processInfo, windowPlacement));
+        _windows.Add(new WindowInfo(windowHandle, windowTitle, processInfo, windowPlacement));
         return true;
     }
     
-    [DllImport("user32.dll")]
-    [return: MarshalAs(UnmanagedType.Bool)]
-    static extern bool EnumWindows(EnumWindowsProc lpEnumFunc, IntPtr lParam);
     
-    private delegate bool EnumWindowsProc(IntPtr windowHandle, IntPtr lParam);
-    
-    [DllImport("user32.dll")]
-    [return: MarshalAs(UnmanagedType.Bool)]
-    public static extern bool GetWindowPlacement(IntPtr windowHandle, ref WindowPlacement lpwndpl);
-    
-    [DllImport("user32.dll")]
-    private static extern uint GetWindowThreadProcessId(IntPtr windowHandle, out uint lpdwProcessId);
-
-    
-    [DllImport("user32.dll", CharSet = CharSet.Auto)]
-    static extern IntPtr SendMessage(IntPtr windowHandle, uint message, IntPtr wParam, [Out] StringBuilder lParam);
-    
-    public static string GetWindowTextRaw(IntPtr windowHandle)
-    {
-        // ReSharper disable twice InconsistentNaming
-        const uint WM_GETTEXTLENGTH = 0x000E;
-        const uint WM_GETTEXT = 0x000D;
-        // Allocate correct string length first
-        int length = (int)SendMessage(windowHandle, WM_GETTEXTLENGTH, IntPtr.Zero, null);
-        StringBuilder sb = new (length + 1);
-        SendMessage(windowHandle, WM_GETTEXT, sb.Capacity, sb);
-        return sb.ToString();
-    }
 
     public void Dispose()
     {

OBSBlur/Window/WindowManagerUser32Dll.cs

@@ -0,0 +1,65 @@
+using System.Runtime.InteropServices;
+using System.Text;
+
+namespace OBSBlur.Window;
+
+public partial class WindowManager
+{
+    [DllImport("user32.dll")]
+    private static extern IntPtr GetForegroundWindow();
+    
+    [DllImport("user32.dll", SetLastError = true)]
+    static extern IntPtr GetWindow(IntPtr hWnd, uint uCmd);
+    
+    [DllImport("user32.dll", SetLastError = true)]
+    static extern IntPtr GetDesktopWindow();
+    
+    [DllImport("user32.dll")]
+    static extern IntPtr GetTopWindow(IntPtr hWnd);
+    static List<IntPtr> GetWindowZOrder()
+    {
+        const uint GW_HWNDNEXT = 2;
+        const uint GW_HWNDLAST = 1;
+        IntPtr desktopWindow = GetDesktopWindow();
+        IntPtr topWindow = GetTopWindow(desktopWindow);
+        IntPtr bottomWindow = GetWindow(topWindow, GW_HWNDLAST);
+        
+        IntPtr currentWindow = topWindow;
+        List<IntPtr> order = new();
+        do
+        {
+            order.Add(currentWindow);
+        } while ((currentWindow = GetWindow(currentWindow, GW_HWNDNEXT)) != bottomWindow);
+
+        return order;
+    }
+    
+    [DllImport("user32.dll")]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    static extern bool EnumWindows(EnumWindowsProc lpEnumFunc, IntPtr lParam);
+
+    private delegate bool EnumWindowsProc(IntPtr windowHandle, IntPtr lParam);
+    
+    [DllImport("user32.dll")]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    public static extern bool GetWindowPlacement(IntPtr windowHandle, ref WindowPlacement lpwndpl);
+    
+    [DllImport("user32.dll")]
+    private static extern uint GetWindowThreadProcessId(IntPtr windowHandle, out uint lpdwProcessId);
+
+    
+    [DllImport("user32.dll", CharSet = CharSet.Auto)]
+    static extern IntPtr SendMessage(IntPtr windowHandle, uint message, IntPtr wParam, [Out] StringBuilder lParam);
+    
+    public static string GetWindowTextRaw(IntPtr windowHandle)
+    {
+        // ReSharper disable twice InconsistentNaming
+        const uint WM_GETTEXTLENGTH = 0x000E;
+        const uint WM_GETTEXT = 0x000D;
+        // Allocate correct string length first
+        int length = (int)SendMessage(windowHandle, WM_GETTEXTLENGTH, IntPtr.Zero, null);
+        StringBuilder sb = new (length + 1);
+        SendMessage(windowHandle, WM_GETTEXT, sb.Capacity, sb);
+        return sb.ToString();
+    }
+}