Always on top: Add transparent support for on topped window (#44815)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request
Transparency support (best-effort)
> Not every window can be made transparent. Transparency is applied on a
best-effort basis and depends on how the target app/window is built and
rendered.

## When it may not work
* Windows with special rendering pipelines (e.g., certain
hardware-accelerated / compositor-managed surfaces).
* Some tool/popup/owned windows where the foreground window isn’t the
actual surface being drawn.

## How it works (high-level)
* Resolve the best target window (preferring the top-level/root window
over transient children).
* Apply Windows’ standard layered-window alpha mechanism (per-window
opacity) to adjust transparency.
* When unpinned, Restore the original opacity/state when possible.

If transparency doesn’t change, it means the window doesn’t support this
mechanism in its current configuration.
<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist

- [X] Closes: 
#43278 
#42929
#28773

<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed


https://github.com/user-attachments/assets/c97a87f2-3126-4e19-990f-8c684dbeb631

<img width="1119" height="426" alt="image"
src="https://github.com/user-attachments/assets/547671ee-81d3-4c94-8199-bf0c4b1b7760"
/>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

.github/actions/spell-check/expect.txt

@@ -1532,6 +1532,7 @@ riid
 RKey
 RNumber
 rollups
+ROOTOWNER
 rop
 ROUNDSMALL
 ROWSETEXT

src/common/interop/shared_constants.h

@@ -72,6 +72,10 @@ namespace CommonSharedConstants
 
     const wchar_t ALWAYS_ON_TOP_TERMINATE_EVENT[] = L"Local\\AlwaysOnTopTerminateEvent-cfdf1eae-791f-4953-8021-2f18f3837eae";
 
+    const wchar_t ALWAYS_ON_TOP_INCREASE_OPACITY_EVENT[] = L"Local\\AlwaysOnTopIncreaseOpacityEvent-a1b2c3d4-e5f6-7890-abcd-ef1234567890";
+
+    const wchar_t ALWAYS_ON_TOP_DECREASE_OPACITY_EVENT[] = L"Local\\AlwaysOnTopDecreaseOpacityEvent-b2c3d4e5-f6a7-8901-bcde-f12345678901";
+
     // Path to the event used by PowerAccent
     const wchar_t POWERACCENT_EXIT_EVENT[] = L"Local\\PowerToysPowerAccentExitEvent-53e93389-d19a-4fbb-9b36-1981c8965e17";
 

src/modules/alwaysontop/AlwaysOnTop/AlwaysOnTop.cpp

@@ -153,9 +153,21 @@ LRESULT AlwaysOnTop::WndProc(HWND window, UINT message, WPARAM wparam, LPARAM lp
 {
     if (message == WM_HOTKEY)
     {
+        int hotkeyId = static_cast<int>(wparam);
         if (HWND fw{ GetForegroundWindow() })
         {
-            ProcessCommand(fw);
+            if (hotkeyId == static_cast<int>(HotkeyId::Pin))
+            {
+                ProcessCommand(fw);
+            }
+            else if (hotkeyId == static_cast<int>(HotkeyId::IncreaseOpacity))
+            {
+                StepWindowTransparency(fw, Settings::transparencyStep);
+            }
+            else if (hotkeyId == static_cast<int>(HotkeyId::DecreaseOpacity))
+            {
+                StepWindowTransparency(fw, -Settings::transparencyStep);
+            }
         }
     }
     else if (message == WM_PRIV_SETTINGS_CHANGED)
@@ -191,6 +203,10 @@ void AlwaysOnTop::ProcessCommand(HWND window)
                 m_topmostWindows.erase(iter);
             }
 
+            // Restore transparency when unpinning
+            RestoreWindowAlpha(window);
+            m_windowOriginalLayeredState.erase(window);
+
             Trace::AlwaysOnTop::UnpinWindow();
         }
     }
@@ -200,6 +216,7 @@ void AlwaysOnTop::ProcessCommand(HWND window)
         {
             soundType = Sound::Type::On;
             AssignBorder(window);
+            
             Trace::AlwaysOnTop::PinWindow();
         }
     }
@@ -269,11 +286,22 @@ void AlwaysOnTop::RegisterHotkey() const
 {
     if (m_useCentralizedLLKH)
     {
+        // All hotkeys are handled by centralized LLKH
         return;
     }
 
+    // Register hotkeys only when not using centralized LLKH
     UnregisterHotKey(m_window, static_cast<int>(HotkeyId::Pin));
+    UnregisterHotKey(m_window, static_cast<int>(HotkeyId::IncreaseOpacity));
+    UnregisterHotKey(m_window, static_cast<int>(HotkeyId::DecreaseOpacity));
+
+    // Register pin hotkey
     RegisterHotKey(m_window, static_cast<int>(HotkeyId::Pin), AlwaysOnTopSettings::settings().hotkey.get_modifiers(), AlwaysOnTopSettings::settings().hotkey.get_code());
+
+    // Register transparency hotkeys using the same modifiers as the pin hotkey
+    UINT modifiers = AlwaysOnTopSettings::settings().hotkey.get_modifiers();
+    RegisterHotKey(m_window, static_cast<int>(HotkeyId::IncreaseOpacity), modifiers, VK_OEM_PLUS);
+    RegisterHotKey(m_window, static_cast<int>(HotkeyId::DecreaseOpacity), modifiers, VK_OEM_MINUS);
 }
 
 void AlwaysOnTop::RegisterLLKH()
@@ -285,6 +313,8 @@ void AlwaysOnTop::RegisterLLKH()
 	
     m_hPinEvent = CreateEventW(nullptr, false, false, CommonSharedConstants::ALWAYS_ON_TOP_PIN_EVENT);
     m_hTerminateEvent = CreateEventW(nullptr, false, false, CommonSharedConstants::ALWAYS_ON_TOP_TERMINATE_EVENT);
+    m_hIncreaseOpacityEvent = CreateEventW(nullptr, false, false, CommonSharedConstants::ALWAYS_ON_TOP_INCREASE_OPACITY_EVENT);
+    m_hDecreaseOpacityEvent = CreateEventW(nullptr, false, false, CommonSharedConstants::ALWAYS_ON_TOP_DECREASE_OPACITY_EVENT);
 
     if (!m_hPinEvent)
     {
@@ -298,30 +328,54 @@ void AlwaysOnTop::RegisterLLKH()
         return;
     }
 
-    HANDLE handles[2] = { m_hPinEvent,
+    if (!m_hIncreaseOpacityEvent)
-                          m_hTerminateEvent };
+    {
+        Logger::warn(L"Failed to create increaseOpacityEvent. {}", get_last_error_or_default(GetLastError()));
+    }
+
+    if (!m_hDecreaseOpacityEvent)
+    {
+        Logger::warn(L"Failed to create decreaseOpacityEvent. {}", get_last_error_or_default(GetLastError()));
+    }
+
+    HANDLE handles[4] = { m_hPinEvent,
+                          m_hTerminateEvent,
+                          m_hIncreaseOpacityEvent,
+                          m_hDecreaseOpacityEvent };
 
     m_thread = std::thread([this, handles]() {
         MSG msg;
         while (m_running)
         {
-            DWORD dwEvt = MsgWaitForMultipleObjects(2, handles, false, INFINITE, QS_ALLINPUT);
+            DWORD dwEvt = MsgWaitForMultipleObjects(4, handles, false, INFINITE, QS_ALLINPUT);
             if (!m_running)
             {
                 break;
             }
             switch (dwEvt)
             {
-            case WAIT_OBJECT_0:
+            case WAIT_OBJECT_0: // Pin event
                 if (HWND fw{ GetForegroundWindow() })
                 {
                     ProcessCommand(fw);
                 }
                 break;
-            case WAIT_OBJECT_0 + 1:
+            case WAIT_OBJECT_0 + 1: // Terminate event
                 PostThreadMessage(m_mainThreadId, WM_QUIT, 0, 0);
                 break;
-            case WAIT_OBJECT_0 + 2:
+            case WAIT_OBJECT_0 + 2: // Increase opacity event
+                if (HWND fw{ GetForegroundWindow() })
+                {
+                    StepWindowTransparency(fw, Settings::transparencyStep);
+                }
+                break;
+            case WAIT_OBJECT_0 + 3: // Decrease opacity event
+                if (HWND fw{ GetForegroundWindow() })
+                {
+                    StepWindowTransparency(fw, -Settings::transparencyStep);
+                }
+                break;
+            case WAIT_OBJECT_0 + 4: // Message queue
                 if (PeekMessageW(&msg, nullptr, 0, 0, PM_REMOVE))
                 {
                     TranslateMessage(&msg);
@@ -370,9 +424,12 @@ void AlwaysOnTop::UnpinAll()
         {
             Logger::error(L"Unpinning topmost window failed");
         }
+        // Restore transparency when unpinning all
+        RestoreWindowAlpha(topWindow);
     }
 
     m_topmostWindows.clear();
+    m_windowOriginalLayeredState.clear();
 }
 
 void AlwaysOnTop::CleanUp()
@@ -456,6 +513,7 @@ void AlwaysOnTop::HandleWinHookEvent(WinHookEvent* data) noexcept
     for (const auto window : toErase)
     {
         m_topmostWindows.erase(window);
+        m_windowOriginalLayeredState.erase(window);
     }
 
     switch (data->event)
@@ -556,4 +614,166 @@ void AlwaysOnTop::RefreshBorders()
             }
         }
     }
+}
+
+HWND AlwaysOnTop::ResolveTransparencyTargetWindow(HWND window)
+{
+    if (!window || !IsWindow(window))
+    {
+        return nullptr;
+    }
+
+    // Only allow transparency changes on pinned windows
+    if (!IsPinned(window))
+    {
+        return nullptr;
+    }
+
+    return window;
+}
+
+
+void AlwaysOnTop::StepWindowTransparency(HWND window, int delta)
+{
+    HWND targetWindow = ResolveTransparencyTargetWindow(window);
+    if (!targetWindow)
+    {
+        return;
+    }
+
+    int currentTransparency = Settings::maxTransparencyPercentage;
+    LONG exStyle = GetWindowLong(targetWindow, GWL_EXSTYLE);
+    if (exStyle & WS_EX_LAYERED)
+    {
+        BYTE alpha = 255;
+        if (GetLayeredWindowAttributes(targetWindow, nullptr, &alpha, nullptr))
+        {
+            currentTransparency = (alpha * 100) / 255;
+        }
+    }
+
+    int newTransparency = (std::max)(Settings::minTransparencyPercentage, 
+                                     (std::min)(Settings::maxTransparencyPercentage, currentTransparency + delta));
+
+    if (newTransparency != currentTransparency)
+    {
+        ApplyWindowAlpha(targetWindow, newTransparency);
+
+        if (AlwaysOnTopSettings::settings().enableSound)
+        {
+            m_sound.Play(delta > 0 ? Sound::Type::IncreaseOpacity : Sound::Type::DecreaseOpacity);
+        }
+
+        Logger::debug(L"Transparency adjusted to {}%", newTransparency);
+    }
+}
+
+void AlwaysOnTop::ApplyWindowAlpha(HWND window, int percentage)
+{
+    if (!window || !IsWindow(window))
+    {
+        return;
+    }
+    
+    percentage = (std::max)(Settings::minTransparencyPercentage, 
+                            (std::min)(Settings::maxTransparencyPercentage, percentage));
+
+    LONG exStyle = GetWindowLong(window, GWL_EXSTYLE);
+    bool isCurrentlyLayered = (exStyle & WS_EX_LAYERED) != 0;
+
+    // Cache original state on first transparency application
+    if (m_windowOriginalLayeredState.find(window) == m_windowOriginalLayeredState.end())
+    {
+        WindowLayeredState state;
+        state.hadLayeredStyle = isCurrentlyLayered;
+        
+        if (isCurrentlyLayered)
+        {
+            BYTE alpha = 255;
+            COLORREF colorKey = 0;
+            DWORD flags = 0;
+            if (GetLayeredWindowAttributes(window, &colorKey, &alpha, &flags))
+            {
+                state.originalAlpha = alpha;
+                state.usedColorKey = (flags & LWA_COLORKEY) != 0;
+                state.colorKey = colorKey;
+            }
+            else
+            {
+                Logger::warn(L"GetLayeredWindowAttributes failed for layered window, skipping");
+                return;
+            }
+        }
+        m_windowOriginalLayeredState[window] = state;
+    }
+
+    // Clear WS_EX_LAYERED first to ensure SetLayeredWindowAttributes works
+    if (isCurrentlyLayered)
+    {
+        SetWindowLong(window, GWL_EXSTYLE, exStyle & ~WS_EX_LAYERED);
+        SetWindowPos(window, nullptr, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER | SWP_FRAMECHANGED);
+        exStyle = GetWindowLong(window, GWL_EXSTYLE);
+    }
+
+    BYTE alphaValue = static_cast<BYTE>((255 * percentage) / 100);
+    SetWindowLong(window, GWL_EXSTYLE, exStyle | WS_EX_LAYERED);
+    SetLayeredWindowAttributes(window, 0, alphaValue, LWA_ALPHA);
+}
+
+void AlwaysOnTop::RestoreWindowAlpha(HWND window)
+{
+    if (!window || !IsWindow(window))
+    {
+        return;
+    }
+
+    LONG exStyle = GetWindowLong(window, GWL_EXSTYLE);
+    auto it = m_windowOriginalLayeredState.find(window);
+    
+    if (it != m_windowOriginalLayeredState.end())
+    {
+        const auto& originalState = it->second;
+        
+        if (originalState.hadLayeredStyle)
+        {
+            // Window originally had WS_EX_LAYERED - restore original attributes
+            // Clear and re-add to ensure clean state
+            if (exStyle & WS_EX_LAYERED)
+            {
+                SetWindowLong(window, GWL_EXSTYLE, exStyle & ~WS_EX_LAYERED);
+                exStyle = GetWindowLong(window, GWL_EXSTYLE);
+            }
+            SetWindowLong(window, GWL_EXSTYLE, exStyle | WS_EX_LAYERED);
+            
+            // Restore original alpha and/or color key
+            DWORD flags = LWA_ALPHA;
+            if (originalState.usedColorKey)
+            {
+                flags |= LWA_COLORKEY;
+            }
+            SetLayeredWindowAttributes(window, originalState.colorKey, originalState.originalAlpha, flags);
+            SetWindowPos(window, nullptr, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER | SWP_FRAMECHANGED);
+        }
+        else
+        {
+            // Window originally didn't have WS_EX_LAYERED - remove it completely
+            if (exStyle & WS_EX_LAYERED)
+            {
+                SetLayeredWindowAttributes(window, 0, 255, LWA_ALPHA);
+                SetWindowLong(window, GWL_EXSTYLE, exStyle & ~WS_EX_LAYERED);
+                SetWindowPos(window, nullptr, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER | SWP_FRAMECHANGED);
+            }
+        }
+        
+        m_windowOriginalLayeredState.erase(it);
+    }
+    else
+    {
+        // Fallback: no cached state, just remove layered style
+        if (exStyle & WS_EX_LAYERED)
+        {
+            SetLayeredWindowAttributes(window, 0, 255, LWA_ALPHA);
+            SetWindowLong(window, GWL_EXSTYLE, exStyle & ~WS_EX_LAYERED);
+        }
+    }
 }

src/modules/alwaysontop/AlwaysOnTop/AlwaysOnTop.h

@@ -10,6 +10,7 @@
 
 #include <common/hooks/WinHookEvent.h>
 #include <common/notifications/NotificationUtil.h>
+#include <common/utils/window.h>
 
 class AlwaysOnTop : public SettingsObserver
 {
@@ -38,6 +39,8 @@ private:
     enum class HotkeyId : int
     {
         Pin = 1,
+        IncreaseOpacity = 2,
+        DecreaseOpacity = 3,
     };
 
     static inline AlwaysOnTop* s_instance = nullptr;
@@ -48,8 +51,20 @@ private:
     HWND m_window{ nullptr };
     HINSTANCE m_hinstance;
     std::map<HWND, std::unique_ptr<WindowBorder>> m_topmostWindows{};
+    
+    // Store original window layered state for proper restoration
+    struct WindowLayeredState {
+        bool hadLayeredStyle = false;
+        BYTE originalAlpha = 255;
+        bool usedColorKey = false;
+        COLORREF colorKey = 0;
+    };
+    std::map<HWND, WindowLayeredState> m_windowOriginalLayeredState{};
+    
     HANDLE m_hPinEvent;
     HANDLE m_hTerminateEvent;
+    HANDLE m_hIncreaseOpacityEvent;
+    HANDLE m_hDecreaseOpacityEvent;
     DWORD m_mainThreadId;
     std::thread m_thread;
     const bool m_useCentralizedLLKH;
@@ -78,6 +93,12 @@ private:
     bool AssignBorder(HWND window);
     void RefreshBorders();
 
+    // Transparency methods
+    HWND ResolveTransparencyTargetWindow(HWND window);
+    void StepWindowTransparency(HWND window, int delta);
+    void ApplyWindowAlpha(HWND window, int percentage);
+    void RestoreWindowAlpha(HWND window);
+
     virtual void SettingsUpdate(SettingId type) override;
 
     static void CALLBACK WinHookProc(HWINEVENTHOOK winEventHook,

src/modules/alwaysontop/AlwaysOnTop/Settings.h

@@ -15,6 +15,9 @@ class SettingsObserver;
 struct Settings
 {
     PowerToysSettings::HotkeyObject hotkey = PowerToysSettings::HotkeyObject::from_settings(true, true, false, false, 84); // win + ctrl + T
+    static constexpr int minTransparencyPercentage = 20; // minimum transparency (can't go below 20%)
+    static constexpr int maxTransparencyPercentage = 100; // maximum (fully opaque)
+    static constexpr int transparencyStep = 10; // step size for +/- adjustment
     bool enableFrame = true;
     bool enableSound = true;
     bool roundCornersEnabled = true;

src/modules/alwaysontop/AlwaysOnTop/Sound.h

@@ -2,7 +2,6 @@
 
 #include "pch.h"
 
-#include <atomic>
 #include <mmsystem.h> // sound
 
 class Sound
@@ -12,12 +11,10 @@ public:
     {
         On,
         Off,
+        IncreaseOpacity,
+        DecreaseOpacity,
     };
     
-    Sound()
-        : isPlaying(false)
-    {}
-
     void Play(Type type)
     {
         BOOL success = false;
@@ -29,6 +26,12 @@ public:
         case Type::Off:
             success = PlaySound(TEXT("Media\\Speech Sleep.wav"), NULL, SND_FILENAME | SND_ASYNC);
             break;
+        case Type::IncreaseOpacity:
+            success = PlaySound(TEXT("Media\\Windows Hardware Insert.wav"), NULL, SND_FILENAME | SND_ASYNC);
+            break;
+        case Type::DecreaseOpacity:
+            success = PlaySound(TEXT("Media\\Windows Hardware Remove.wav"), NULL, SND_FILENAME | SND_ASYNC);
+            break;
         default:
             break;
         }
@@ -38,7 +41,4 @@ public:
             Logger::error(L"Sound playing error");
         }
     }
-
-private:
-    std::atomic<bool> isPlaying;
 };

src/modules/alwaysontop/AlwaysOnTopModuleInterface/dllmain.cpp

@@ -105,17 +105,28 @@ public:
         }
     }
 
-    virtual bool on_hotkey(size_t /*hotkeyId*/) override
+    virtual bool on_hotkey(size_t hotkeyId) override
     {
         if (m_enabled)
         {
-            Logger::trace(L"AlwaysOnTop hotkey pressed");
+            Logger::trace(L"AlwaysOnTop hotkey pressed, id={}", hotkeyId);
             if (!is_process_running())
             {
                 Enable();
             }
 
-            SetEvent(m_hPinEvent);
+            if (hotkeyId == 0)
+            {
+                SetEvent(m_hPinEvent);
+            }
+            else if (hotkeyId == 1)
+            {
+                SetEvent(m_hIncreaseOpacityEvent);
+            }
+            else if (hotkeyId == 2)
+            {
+                SetEvent(m_hDecreaseOpacityEvent);
+            }
 
             return true;
         }
@@ -125,19 +136,48 @@ public:
 
     virtual size_t get_hotkeys(Hotkey* hotkeys, size_t buffer_size) override
     {
+        size_t count = 0;
+        
+        // Hotkey 0: Pin/Unpin (e.g., Win+Ctrl+T)
         if (m_hotkey.key)
         {
-            if (hotkeys && buffer_size >= 1)
+            if (hotkeys && buffer_size > count)
             {
-                hotkeys[0] = m_hotkey;
+                hotkeys[count] = m_hotkey;
+                Logger::trace(L"AlwaysOnTop hotkey[0]: win={}, ctrl={}, shift={}, alt={}, key={}", 
+                    m_hotkey.win, m_hotkey.ctrl, m_hotkey.shift, m_hotkey.alt, m_hotkey.key);
             }
+            count++;
+        }
 
-            return 1;
+        // Hotkey 1: Increase opacity (same modifiers + VK_OEM_PLUS '=')
-        }
+        if (m_hotkey.key)
-        else
         {
-            return 0;
+            if (hotkeys && buffer_size > count)
+            {
+                hotkeys[count] = m_hotkey;
+                hotkeys[count].key = VK_OEM_PLUS; // '=' key
+                Logger::trace(L"AlwaysOnTop hotkey[1] (increase opacity): win={}, ctrl={}, shift={}, alt={}, key={}", 
+                    hotkeys[count].win, hotkeys[count].ctrl, hotkeys[count].shift, hotkeys[count].alt, hotkeys[count].key);
+            }
+            count++;
         }
+
+        // Hotkey 2: Decrease opacity (same modifiers + VK_OEM_MINUS '-')
+        if (m_hotkey.key)
+        {
+            if (hotkeys && buffer_size > count)
+            {
+                hotkeys[count] = m_hotkey;
+                hotkeys[count].key = VK_OEM_MINUS; // '-' key
+                Logger::trace(L"AlwaysOnTop hotkey[2] (decrease opacity): win={}, ctrl={}, shift={}, alt={}, key={}", 
+                    hotkeys[count].win, hotkeys[count].ctrl, hotkeys[count].shift, hotkeys[count].alt, hotkeys[count].key);
+            }
+            count++;
+        }
+
+        Logger::trace(L"AlwaysOnTop get_hotkeys returning count={}", count);
+        return count;
     }
 
     // Enable the powertoy
@@ -175,6 +215,8 @@ public:
         app_key = NonLocalizable::ModuleKey;
         m_hPinEvent = CreateDefaultEvent(CommonSharedConstants::ALWAYS_ON_TOP_PIN_EVENT);
         m_hTerminateEvent = CreateDefaultEvent(CommonSharedConstants::ALWAYS_ON_TOP_TERMINATE_EVENT);
+        m_hIncreaseOpacityEvent = CreateDefaultEvent(CommonSharedConstants::ALWAYS_ON_TOP_INCREASE_OPACITY_EVENT);
+        m_hDecreaseOpacityEvent = CreateDefaultEvent(CommonSharedConstants::ALWAYS_ON_TOP_DECREASE_OPACITY_EVENT);
         init_settings();
     }
 
@@ -292,6 +334,8 @@ private:
     // Handle to event used to pin/unpin windows
     HANDLE m_hPinEvent;
     HANDLE m_hTerminateEvent;
+    HANDLE m_hIncreaseOpacityEvent;
+    HANDLE m_hDecreaseOpacityEvent;
 };
 
 extern "C" __declspec(dllexport) PowertoyModuleIface* __cdecl powertoy_create()

src/settings-ui/Settings.UI/SettingsXAML/Views/AlwaysOnTopPage.xaml

@@ -38,6 +38,24 @@
                             </tkcontrols:SettingsCard>
                         </tkcontrols:SettingsExpander.Items>
                     </tkcontrols:SettingsExpander>
+                    <tkcontrols:SettingsExpander
+                        x:Uid="AlwaysOnTop_TransparencyInfo"
+                        HeaderIcon="{ui:FontIcon Glyph=&#xE790;}"
+                        IsExpanded="True">
+                        <tkcontrols:SettingsExpander.Items>
+                            <tkcontrols:SettingsCard ContentAlignment="Left">
+                                <controls:ShortcutWithTextLabelControl x:Uid="AlwaysOnTop_IncreaseOpacity" Keys="{x:Bind ViewModel.IncreaseOpacityKeysList, Mode=OneWay}" />
+                            </tkcontrols:SettingsCard>
+                            <tkcontrols:SettingsCard ContentAlignment="Left">
+                                <controls:ShortcutWithTextLabelControl x:Uid="AlwaysOnTop_DecreaseOpacity" Keys="{x:Bind ViewModel.DecreaseOpacityKeysList, Mode=OneWay}" />
+                            </tkcontrols:SettingsCard>
+                            <tkcontrols:SettingsCard>
+                                <tkcontrols:SettingsCard.Description>
+                                    <TextBlock x:Uid="AlwaysOnTop_TransparencyRange" Style="{StaticResource SecondaryTextStyle}" />
+                                </tkcontrols:SettingsCard.Description>
+                            </tkcontrols:SettingsCard>
+                        </tkcontrols:SettingsExpander.Items>
+                    </tkcontrols:SettingsExpander>
                 </controls:SettingsGroup>
 
                 <controls:SettingsGroup x:Uid="AlwaysOnTop_Behavior_GroupSettings" IsEnabled="{x:Bind ViewModel.IsEnabled, Mode=OneWay}">

src/settings-ui/Settings.UI/Strings/en-us/Resources.resw

@@ -3240,7 +3240,19 @@ Right-click to remove the key combination, thereby deactivating the shortcut.</v
     <value>Activation shortcut</value>
   </data>
   <data name="AlwaysOnTop_ActivationShortcut.Description" xml:space="preserve">
-    <value>Customize the shortcut to pin or unpin an app window</value>
+    <value>Customize the shortcut to pin or unpin an app window. Use the same modifier keys with + or - to adjust window transparency.</value>
+  </data>
+  <data name="AlwaysOnTop_TransparencyInfo.Header" xml:space="preserve">
+    <value>Transparency adjustment</value>
+  </data>
+  <data name="AlwaysOnTop_IncreaseOpacity.Text" xml:space="preserve">
+    <value>Increase opacity</value>
+  </data>
+  <data name="AlwaysOnTop_DecreaseOpacity.Text" xml:space="preserve">
+    <value>Decrease opacity</value>
+  </data>
+  <data name="AlwaysOnTop_TransparencyRange.Text" xml:space="preserve">
+    <value>Range: 20%-100%</value>
   </data>
   <data name="Oobe_AlwaysOnTop.Title" xml:space="preserve">
     <value>Always On Top</value>

src/settings-ui/Settings.UI/ViewModels/AlwaysOnTopViewModel.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Generic;
 using System.Globalization;
+using System.Linq;
 using System.Runtime.CompilerServices;
 using System.Text.Json;
 using global::PowerToys.GPOWrapper;
@@ -133,6 +134,10 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
                     Settings.Properties.Hotkey.Value = _hotkey;
                     NotifyPropertyChanged();
 
+                    // Also notify that transparency keys have changed
+                    OnPropertyChanged(nameof(IncreaseOpacityKeysList));
+                    OnPropertyChanged(nameof(DecreaseOpacityKeysList));
+
                     // Using InvariantCulture as this is an IPC message
                     SendConfigMSG(
                         string.Format(
@@ -289,6 +294,62 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
             }
         }
 
+        /// <summary>
+        /// Gets the keys list for increasing window opacity (modifier keys + "+").
+        /// </summary>
+        public List<object> IncreaseOpacityKeysList
+        {
+            get
+            {
+                var keys = GetModifierKeysList();
+                keys.Add("+");
+                return keys;
+            }
+        }
+
+        /// <summary>
+        /// Gets the keys list for decreasing window opacity (modifier keys + "-").
+        /// </summary>
+        public List<object> DecreaseOpacityKeysList
+        {
+            get
+            {
+                var keys = GetModifierKeysList();
+                keys.Add("-");
+                return keys;
+            }
+        }
+
+        /// <summary>
+        /// Gets only the modifier keys from the current hotkey setting.
+        /// </summary>
+        private List<object> GetModifierKeysList()
+        {
+            var modifierKeys = new List<object>();
+
+            if (_hotkey.Win)
+            {
+                modifierKeys.Add(92); // The Windows key
+            }
+
+            if (_hotkey.Ctrl)
+            {
+                modifierKeys.Add("Ctrl");
+            }
+
+            if (_hotkey.Alt)
+            {
+                modifierKeys.Add("Alt");
+            }
+
+            if (_hotkey.Shift)
+            {
+                modifierKeys.Add(16); // The Shift key
+            }
+
+            return modifierKeys;
+        }
+
         public void NotifyPropertyChanged([CallerMemberName] string propertyName = null)
         {
             OnPropertyChanged(propertyName);