Preserve Windows key shortcuts

Author: nakorndev

AGENTS.md

@@ -23,6 +23,8 @@ Primary goals:
   risk or complexity.
 - Preserve the low-level keyboard hook behavior in `Program.cs`.
 - Do not send `Win+Space` as the switching implementation.
+- Windows-key shortcuts such as `Win+L` and `Win+Shift+S` must always pass
+  through untouched.
 - Prefer Win32/UI Automation APIs over simulated key chords for language
   switching, caret detection, and state management.
 - Keyboard-triggered indicators should anchor to the text insertion caret when

CapsLang.csproj

@@ -14,9 +14,9 @@
     <Authors>NakornCode</Authors>
     <Company>NakornCode</Company>
     <Copyright>Copyright © NakornCode</Copyright>
-    <Version>0.1.1</Version>
-    <FileVersion>0.1.1.0</FileVersion>
-    <AssemblyVersion>0.1.1.0</AssemblyVersion>
+    <Version>0.1.2</Version>
+    <FileVersion>0.1.2.0</FileVersion>
+    <AssemblyVersion>0.1.2.0</AssemblyVersion>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Interop.UIAutomationClient" Version="10.19041.0" />

Program.cs

@@ -21,8 +21,11 @@ internal static class Program
     private const int VK_CAPITAL = 0x14;
     private const int VK_SHIFT = 0x10;
     private const int VK_CONTROL = 0x11;
+    private const int VK_LWIN = 0x5B;
+    private const int VK_RWIN = 0x5C;
     private const int WM_INPUTLANGCHANGEREQUEST = 0x0050;
     private const int INPUTLANGCHANGE_FORWARD = 0x0002;
+    private const int LLKHF_INJECTED = 0x10;
     private static readonly IntPtr HKL_NEXT = new(1);
 
     private static IntPtr hookId = IntPtr.Zero;
@@ -167,43 +170,51 @@ private static IntPtr SetHook(LowLevelKeyboardProc proc)
 
     private static IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
     {
+        if (nCode < 0 || IsWindowsKeyDown())
+        {
+            return CallNextHookEx(hookId, nCode, wParam, lParam);
+        }
+
         if (!appSettings.IsCapsLangEnabled)
         {
             return CallNextHookEx(hookId, nCode, wParam, lParam);
         }
 
-        if (nCode >= 0)
+        var message = wParam.ToInt32();
+        var keyboardEvent = Marshal.PtrToStructure<KBDLLHOOKSTRUCT>(lParam);
+        var vkCode = keyboardEvent.vkCode;
+
+        if (vkCode == VK_CAPITAL)
         {
-            var message = wParam.ToInt32();
-            var vkCode = Marshal.ReadInt32(lParam);
+            if ((keyboardEvent.flags & LLKHF_INJECTED) != 0)
+            {
+                return CallNextHookEx(hookId, nCode, wParam, lParam);
+            }
 
-            if (vkCode == VK_CAPITAL)
+            if (message is WM_KEYDOWN or WM_SYSKEYDOWN)
             {
-                if (message is WM_KEYDOWN or WM_SYSKEYDOWN)
+                if (IsKeyDown(VK_CONTROL))
                 {
-                    if (IsKeyDown(VK_CONTROL))
-                    {
-                        ForceCapsLockOff();
-                        ShowIndicator("CAPS OFF", force: true);
-                    }
-                    else if (IsKeyDown(VK_SHIFT))
-                    {
-                        ToggleCapsLock();
-                        ShowIndicator(IsCapsLockOn() ? "CAPS ON" : "CAPS OFF", force: true);
-                    }
-                    else
-                    {
-                        ForceCapsLockOff();
-                        SwitchToNextInputLanguage();
-                        languagePopupTimer?.Stop();
-                        languagePopupTimer?.Start();
-                    }
+                    ForceCapsLockOff();
+                    ShowIndicator("CAPS OFF", force: true);
                 }
-
-                if (message is WM_KEYDOWN or WM_KEYUP or WM_SYSKEYDOWN or WM_SYSKEYUP)
+                else if (IsKeyDown(VK_SHIFT))
                 {
-                    return new IntPtr(1);
+                    SetCapsLockState(!IsCapsLockOn());
+                    ShowIndicator(IsCapsLockOn() ? "CAPS ON" : "CAPS OFF", force: true);
                 }
+                else
+                {
+                    ForceCapsLockOff();
+                    SwitchToNextInputLanguage();
+                    languagePopupTimer?.Stop();
+                    languagePopupTimer?.Start();
+                }
+            }
+
+            if (message is WM_KEYDOWN or WM_KEYUP or WM_SYSKEYDOWN or WM_SYSKEYUP)
+            {
+                return new IntPtr(1);
             }
         }
 
@@ -221,10 +232,7 @@ private static void SwitchToNextInputLanguage()
 
     private static void ForceCapsLockOff()
     {
-        if (IsCapsLockOn())
-        {
-            ToggleCapsLock();
-        }
+        SetCapsLockState(false);
     }
 
     private static bool IsCapsLockOn()
@@ -237,7 +245,20 @@ private static bool IsKeyDown(int virtualKey)
         return (GetAsyncKeyState(virtualKey) & 0x8000) != 0;
     }
 
-    private static void ToggleCapsLock()
+    private static bool IsWindowsKeyDown()
+    {
+        return IsKeyDown(VK_LWIN) || IsKeyDown(VK_RWIN);
+    }
+
+    private static void SetCapsLockState(bool enabled)
+    {
+        if (IsCapsLockOn() != enabled)
+        {
+            SetKeyboardStateCapsLock(enabled);
+        }
+    }
+
+    private static void SetKeyboardStateCapsLock(bool enabled)
     {
         keybd_event(VK_CAPITAL, 0x45, KEYEVENTF_EXTENDEDKEY, UIntPtr.Zero);
         keybd_event(VK_CAPITAL, 0x45, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, UIntPtr.Zero);
@@ -507,6 +528,16 @@ private static Point GetPointerPopupAnchor()
 
     private delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);
 
+    [StructLayout(LayoutKind.Sequential)]
+    private struct KBDLLHOOKSTRUCT
+    {
+        public int vkCode;
+        public int scanCode;
+        public int flags;
+        public int time;
+        public UIntPtr dwExtraInfo;
+    }
+
     [StructLayout(LayoutKind.Sequential)]
     private struct GUITHREADINFO
     {
@@ -550,10 +581,10 @@ private struct RECT
     private static extern short GetAsyncKeyState(int vKey);
 
     [DllImport("user32.dll")]
-    private static extern void keybd_event(int bVk, byte bScan, uint dwFlags, UIntPtr dwExtraInfo);
+    private static extern IntPtr GetForegroundWindow();
 
     [DllImport("user32.dll")]
-    private static extern IntPtr GetForegroundWindow();
+    private static extern void keybd_event(int bVk, byte bScan, uint dwFlags, UIntPtr dwExtraInfo);
 
     [DllImport("user32.dll")]
     private static extern uint GetWindowThreadProcessId(IntPtr hWnd, out uint lpdwProcessId);

README.md

@@ -12,6 +12,8 @@ shortcuts such as `Win+Space+1` or `Win+Space+D`.
 
 - Use `CapsLock` to switch to the next Windows input language.
 - Keep real CapsLock off during normal typing.
+- Leave normal Windows-key shortcuts such as `Win+L` and `Win+Shift+S`
+  untouched.
 - Show the active Windows input language code near the text insertion caret
   when the active app exposes caret geometry through Windows UI Automation.
 - Avoid mouse-pointer based typing feedback.