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LibreHardwareMonitor-0.9.4/LibreHardwareMonitor/UI/ShowDesktop.cs

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+// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
+// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// Copyright (C) LibreHardwareMonitor and Contributors.
+// Partial Copyright (C) Michael Möller <mmoeller@openhardwaremonitor.org> and Contributors.
+// All Rights Reserved.
+
+using System;
+using System.Runtime.InteropServices;
+using System.Windows.Forms;
+
+namespace LibreHardwareMonitor.UI;
+
+public class ShowDesktop : IDisposable
+{
+    private readonly NativeWindow _referenceWindow;
+    private readonly string _referenceWindowCaption = "LibreHardwareMonitorShowDesktopReferenceWindow";
+    private readonly System.Threading.Timer _timer;
+    private bool _showDesktop;
+
+    /// <summary>
+    /// Prevents a default instance of the <see cref="ShowDesktop" /> class from being created.
+    /// </summary>
+    private ShowDesktop()
+    {
+        // Create a reference window to detect show desktop
+        _referenceWindow = new NativeWindow();
+
+        CreateParams cp = new CreateParams { ExStyle = GadgetWindow.WS_EX_TOOLWINDOW, Caption = _referenceWindowCaption };
+        _referenceWindow.CreateHandle(cp);
+        NativeMethods.SetWindowPos(_referenceWindow.Handle,
+                                   GadgetWindow.HWND_BOTTOM,
+                                   0,
+                                   0,
+                                   0,
+                                   0,
+                                   GadgetWindow.SWP_NOMOVE |
+                                   GadgetWindow.SWP_NOSIZE |
+                                   GadgetWindow.SWP_NOACTIVATE |
+                                   GadgetWindow.SWP_NOSENDCHANGING);
+
+        // start a repeated timer to detect "Show Desktop" events
+        _timer = new System.Threading.Timer(OnTimer, null, System.Threading.Timeout.Infinite, System.Threading.Timeout.Infinite);
+    }
+
+    public delegate void ShowDesktopChangedEventHandler(bool showDesktop);
+
+    private event ShowDesktopChangedEventHandler ShowDesktopChangedEvent;
+
+    // notify when the "show desktop" mode is changed
+    public event ShowDesktopChangedEventHandler ShowDesktopChanged
+    {
+        add
+        {
+            // start the monitor timer when someone is listening
+            if (ShowDesktopChangedEvent == null)
+                StartTimer();
+
+            ShowDesktopChangedEvent += value;
+        }
+        remove
+        {
+            ShowDesktopChangedEvent -= value;
+            // stop the monitor timer if nobody is interested
+            if (ShowDesktopChangedEvent == null)
+                StopTimer();
+        }
+    }
+
+    public static ShowDesktop Instance { get; } = new ShowDesktop();
+
+    /// <inheritdoc />
+    public void Dispose()
+    {
+        _timer?.Dispose();
+        _referenceWindow.ReleaseHandle();
+    }
+
+    private void StartTimer()
+    {
+        _timer.Change(0, 200);
+    }
+
+    private void StopTimer()
+    {
+        _timer.Change(System.Threading.Timeout.Infinite, System.Threading.Timeout.Infinite);
+    }
+
+    // the desktop worker window (if available) can hide the reference window
+    private IntPtr GetDesktopWorkerWindow()
+    {
+        IntPtr shellWindow = NativeMethods.GetShellWindow();
+        if (shellWindow == IntPtr.Zero)
+            return IntPtr.Zero;
+
+
+        NativeMethods.GetWindowThreadProcessId(shellWindow, out int shellId);
+
+        IntPtr workerWindow = IntPtr.Zero;
+        while ((workerWindow = NativeMethods.FindWindowEx(IntPtr.Zero, workerWindow, "WorkerW", null)) != IntPtr.Zero)
+        {
+            NativeMethods.GetWindowThreadProcessId(workerWindow, out int workerId);
+            if (workerId == shellId)
+            {
+                IntPtr window = NativeMethods.FindWindowEx(workerWindow, IntPtr.Zero, "SHELLDLL_DefView", null);
+                if (window != IntPtr.Zero)
+                {
+                    IntPtr desktopWindow = NativeMethods.FindWindowEx(window, IntPtr.Zero, "SysListView32", null);
+                    if (desktopWindow != IntPtr.Zero)
+                        return workerWindow;
+                }
+            }
+        }
+
+        return IntPtr.Zero;
+    }
+
+    private void OnTimer(object state)
+    {
+        bool showDesktopDetected;
+
+        IntPtr workerWindow = GetDesktopWorkerWindow();
+        if (workerWindow != IntPtr.Zero)
+        {
+            // search if the reference window is behind the worker window
+            IntPtr reference = NativeMethods.FindWindowEx(IntPtr.Zero, workerWindow, null, _referenceWindowCaption);
+            showDesktopDetected = reference != IntPtr.Zero;
+        }
+        else
+        {
+            // if there is no worker window, then nothing can hide the reference
+            showDesktopDetected = false;
+        }
+
+        if (_showDesktop != showDesktopDetected)
+        {
+            _showDesktop = showDesktopDetected;
+            ShowDesktopChangedEvent?.Invoke(_showDesktop);
+        }
+    }
+
+    private static class NativeMethods
+    {
+        private const string USER = "user32.dll";
+
+        [DllImport(USER, CallingConvention = CallingConvention.Winapi)]
+        public static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, int X, int Y, int cx, int cy, uint uFlags);
+
+        [DllImport(USER, CallingConvention = CallingConvention.Winapi)]
+        public static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);
+
+        [DllImport(USER, CallingConvention = CallingConvention.Winapi)]
+        public static extern IntPtr GetShellWindow();
+
+        [DllImport(USER, CallingConvention = CallingConvention.Winapi)]
+        public static extern int GetWindowThreadProcessId(IntPtr hWnd, out int processId);
+    }
+}