Fix OpenConsole dark mode for title bar and scrollbars

src/internal/stubs.cpp

@@ -1,27 +1,88 @@
-// Copyright (c) Microsoft Corporation.
-// Licensed under the MIT license.
-
-#include "precomp.h"
-
-#include "../inc/conint.h"
-
-using namespace Microsoft::Console::Internal;
-
-[[nodiscard]] HRESULT ProcessPolicy::CheckAppModelPolicy(const HANDLE /*hToken*/,
-                                                         bool& fIsWrongWayBlocked) noexcept
-{
-    fIsWrongWayBlocked = false;
-    return S_OK;
-}
-
-[[nodiscard]] HRESULT ProcessPolicy::CheckIntegrityLevelPolicy(const HANDLE /*hOtherToken*/,
-                                                               bool& fIsWrongWayBlocked) noexcept
-{
-    fIsWrongWayBlocked = false;
-    return S_OK;
-}
-
-[[nodiscard]] HRESULT Theming::TrySetDarkMode(HWND /*hwnd*/) noexcept
-{
-    return S_FALSE;
-}
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+#include "precomp.h"
+
+#include "../inc/conint.h"
+#include <dwmapi.h>
+#include <uxtheme.h>
+
+// DWMWA_USE_IMMERSIVE_DARK_MODE is defined in newer SDKs, but we define it here
+// for compatibility with older SDKs.
+#ifndef DWMWA_USE_IMMERSIVE_DARK_MODE
+#define DWMWA_USE_IMMERSIVE_DARK_MODE 20
+#endif
+
+using namespace Microsoft::Console::Internal;
+
+[[nodiscard]] HRESULT ProcessPolicy::CheckAppModelPolicy(const HANDLE /*hToken*/,
+                                                         bool& fIsWrongWayBlocked) noexcept
+{
+    fIsWrongWayBlocked = false;
+    return S_OK;
+}
+
+[[nodiscard]] HRESULT ProcessPolicy::CheckIntegrityLevelPolicy(const HANDLE /*hOtherToken*/,
+                                                               bool& fIsWrongWayBlocked) noexcept
+{
+    fIsWrongWayBlocked = false;
+    return S_OK;
+}
+
+// Helper function to check if the system is using a dark theme.
+// This checks the registry for the AppsUseLightTheme value.
+static bool _IsSystemInDarkTheme() noexcept
+{
+    DWORD value = 0;
+    DWORD size = sizeof(value);
+    if (RegGetValueW(
+            HKEY_CURRENT_USER,
+            L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+            L"SystemUsesLightTheme",
+            RRF_RT_DWORD,
+            nullptr,
+            &value,
+            &size) == ERROR_SUCCESS)
+    {
+        // value is 0 for dark theme, 1 for light theme
+        return value == 0;
+    }
+    // Default to light theme if we can't read the registry
+    return false;
+}
+
+[[nodiscard]] HRESULT Theming::TrySetDarkMode(HWND hwnd) noexcept
+{
+    if (hwnd == nullptr)
+    {
+        return E_INVALIDARG;
+    }
+
+    // Check if system is in dark mode
+    const BOOL isDarkMode = _IsSystemInDarkTheme() ? TRUE : FALSE;
+
+    // Set the window attribute for dark mode
+    // This will make the title bar follow the system theme
+    const HRESULT hr = DwmSetWindowAttribute(
+        hwnd,
+        DWMWA_USE_IMMERSIVE_DARK_MODE,
+        &isDarkMode,
+        sizeof(isDarkMode));
+
+    // Set the scroll bar theme to match dark/light mode
+    // "DarkMode_Explorer" is the theme name for dark scrollbars
+    // "Explorer" is the default light theme
+    if (isDarkMode)
+    {
+        // Try to set dark mode theme for scrollbars
+        // This uses the undocumented but widely used DarkMode_Explorer theme
+        SetWindowTheme(hwnd, L"DarkMode_Explorer", nullptr);
+    }
+    else
+    {
+        // Reset to default theme for light mode
+        SetWindowTheme(hwnd, L"Explorer", nullptr);
+    }
+
+    return hr;
+}