Warn if Windows compatibility mode flags are detected on startup

osu.Desktop/OsuGameDesktop.cs

@@ -145,6 +145,9 @@ protected override void LoadComplete()
 
             LoadComponentAsync(new ElevatedPrivilegesChecker(), Add);
 
+            if (OperatingSystem.IsWindows())
+                LoadComponentAsync(new CompatibilityModeChecker(), Add);
+
             osuSchemeLinkIPCChannel = new OsuSchemeLinkIPCChannel(Host, this);
             archiveImportIPCChannel = new ArchiveImportIPCChannel(Host, this);
         }

osu.Desktop/Program.cs

@@ -52,15 +52,24 @@ public static void Main(string[] args)
                 // See https://www.mongodb.com/docs/realm/sdk/dotnet/compatibility/
                 if (windowsVersion.Major < 6 || (windowsVersion.Major == 6 && windowsVersion.Minor <= 2))
                 {
-                    // If users running in compatibility mode becomes more of a common thing, we may want to provide better guidance or even consider
-                    // disabling it ourselves.
-                    // We could also better detect compatibility mode if required:
-                    // https://stackoverflow.com/questions/10744651/how-i-can-detect-if-my-application-is-running-under-compatibility-mode#comment58183249_10744730
-                    SDL.SDL_ShowSimpleMessageBox(SDL.SDL_MessageBoxFlags.SDL_MESSAGEBOX_ERROR,
-                        "Your operating system is too old to run osu!",
-                        "This version of osu! requires at least Windows 8.1 to run.\n"
-                        + "Please upgrade your operating system or consider using an older version of osu!.\n\n"
-                        + "If you are running a newer version of windows, please check you don't have \"Compatibility mode\" turned on for osu!", IntPtr.Zero);
+                    bool isInCompatibilityMode = CompatibilityModeChecker.CheckCompatibilityMode();
+
+                    if (isInCompatibilityMode)
+                    {
+                        SDL.SDL_ShowSimpleMessageBox(SDL.SDL_MessageBoxFlags.SDL_MESSAGEBOX_ERROR,
+                            "osu! is running in compatibility mode",
+                            "osu! is running in compatibility mode. This may cause issues with the game. Please ensure osu! is not set to run in compatibility mode.\n\n"
+                            + "Debug information: " + CompatibilityModeChecker.GetCompatibilityFlags(), IntPtr.Zero);
+                    }
+                    else
+                    {
+                        SDL.SDL_ShowSimpleMessageBox(SDL.SDL_MessageBoxFlags.SDL_MESSAGEBOX_ERROR,
+                            "Your operating system is too old to run osu!",
+                            "This version of osu! requires at least Windows 8.1 to run.\n"
+                            + "Please upgrade your operating system or consider using an older version of osu!.\n\n"
+                            + "If you are running a newer version of windows, please check you don't have \"Compatibility mode\" turned on for osu!", IntPtr.Zero);
+                    }
+
                     return;
                 }
 

osu.Desktop/Windows/CompatibilityModeChecker.cs

@@ -0,0 +1,84 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using System.Linq;
+using System.Runtime.Versioning;
+using Microsoft.Win32;
+using osu.Framework.Allocation;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Sprites;
+using osu.Framework.Logging;
+using osu.Game.Graphics;
+using osu.Game.Localisation;
+using osu.Game.Overlays;
+using osu.Game.Overlays.Notifications;
+
+namespace osu.Desktop.Windows
+{
+    /// <summary>
+    /// Checks if the game is running with windows compatibility optimizations which could cause issues. Displays a warning notification if so.
+    /// </summary>
+    [SupportedOSPlatform("windows")]
+    public partial class CompatibilityModeChecker : Component
+    {
+        [Resolved]
+        private INotificationOverlay notifications { get; set; } = null!;
+
+        [BackgroundDependencyLoader]
+        private void load()
+        {
+            if (!CheckCompatibilityMode()) return;
+
+            notifications.Post(new CompatibilityModeNotification());
+            LogCompatibilityFlags();
+        }
+
+        /// <summary>
+        /// Check if the game is running with windows compatibility optimizations
+        /// </summary>
+        /// <returns>Whether compatibility mode flags are detected or not</returns>
+        public static bool CheckCompatibilityMode()
+        {
+            using var layers = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers");
+
+            return layers != null && layers.GetValueNames().Any(name => name.Equals(Environment.ProcessPath, StringComparison.OrdinalIgnoreCase));
+        }
+
+        /// <summary>
+        /// Log the compatibility flags for the current process if they exist
+        /// </summary>
+        public static void LogCompatibilityFlags()
+        {
+            Logger.Log($"Compatibility flags for {Environment.ProcessPath}: {GetCompatibilityFlags()}");
+        }
+
+        /// <summary>
+        /// Get the compatibility flags for the current process if they exist
+        /// </summary>
+        /// <returns>The compatibility flags</returns>
+        public static string GetCompatibilityFlags()
+        {
+            using var layers = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers");
+
+            return layers?.GetValue(Environment.ProcessPath) as string ?? string.Empty;
+        }
+
+        private partial class CompatibilityModeNotification : SimpleNotification
+        {
+            public override bool IsImportant => true;
+
+            public CompatibilityModeNotification()
+            {
+                Text = WindowsCompatibilityModeCheckerStrings.NotificationText;
+            }
+
+            [BackgroundDependencyLoader]
+            private void load(OsuColour colours)
+            {
+                Icon = FontAwesome.Solid.ShieldAlt;
+                IconContent.Colour = colours.YellowDark;
+            }
+        }
+    }
+}

osu.Game/Localisation/WindowsCompatibilityModeCheckerStrings.cs

@@ -0,0 +1,19 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Localisation;
+
+namespace osu.Game.Localisation
+{
+    public static class WindowsCompatibilityModeCheckerStrings
+    {
+        private const string prefix = @"osu.Game.Resources.Localisation.WindowsCompatibilityModeChecker";
+
+        /// <summary>
+        /// "osu! is running in compatibility mode. This may cause issues with the game. Please ensure osu! is not set to run in compatibility mode."
+        /// </summary>
+        public static LocalisableString NotificationText => new TranslatableString(getKey(@"notification_text"), @"osu! is running in compatibility mode. This may cause issues with the game. Please ensure osu! is not set to run in compatibility mode.");
+
+        private static string getKey(string key) => $@"{prefix}:{key}";
+    }
+}