Rebuild runners (#1725)

experimental/context_menus/windows/runner/win32_window.cpp

@@ -1,13 +1,31 @@
 #include "win32_window.h"
 
+#include <dwmapi.h>
 #include <flutter_windows.h>
 
 #include "resource.h"
 
 namespace {
 
+/// Window attribute that enables dark mode window decorations.
+///
+/// Redefined in case the developer's machine has a Windows SDK older than
+/// version 10.0.22000.0.
+/// See: https://docs.microsoft.com/windows/win32/api/dwmapi/ne-dwmapi-dwmwindowattribute
+#ifndef DWMWA_USE_IMMERSIVE_DARK_MODE
+#define DWMWA_USE_IMMERSIVE_DARK_MODE 20
+#endif
+
 constexpr const wchar_t kWindowClassName[] = L"FLUTTER_RUNNER_WIN32_WINDOW";
 
+/// Registry key for app theme preference.
+///
+/// A value of 0 indicates apps should use dark mode. A non-zero or missing
+/// value indicates apps should use light mode.
+constexpr const wchar_t kGetPreferredBrightnessRegKey[] =
+  L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize";
+constexpr const wchar_t kGetPreferredBrightnessRegValue[] = L"AppsUseLightTheme";
+
 // The number of Win32Window objects that currently exist.
 static int g_active_window_count = 0;
 
@@ -42,7 +60,7 @@ class WindowClassRegistrar {
  public:
   ~WindowClassRegistrar() = default;
 
-  // Returns the singleton registar instance.
+  // Returns the singleton registrar instance.
   static WindowClassRegistrar* GetInstance() {
     if (!instance_) {
       instance_ = new WindowClassRegistrar();
@@ -126,6 +144,8 @@ bool Win32Window::Create(const std::wstring& title,
     return false;
   }
 
+  UpdateTheme(window);
+
   return OnCreate();
 }
 
@@ -192,6 +212,10 @@ Win32Window::MessageHandler(HWND hwnd,
         SetFocus(child_content_);
       }
       return 0;
+
+    case WM_DWMCOLORIZATIONCOLORCHANGED:
+      UpdateTheme(hwnd);
+      return 0;
   }
 
   return DefWindowProc(window_handle_, message, wparam, lparam);
@@ -247,3 +271,18 @@ bool Win32Window::OnCreate() {
 void Win32Window::OnDestroy() {
   // No-op; provided for subclasses.
 }
+
+void Win32Window::UpdateTheme(HWND const window) {
+  DWORD light_mode;
+  DWORD light_mode_size = sizeof(light_mode);
+  LSTATUS result = RegGetValue(HKEY_CURRENT_USER, kGetPreferredBrightnessRegKey,
+                               kGetPreferredBrightnessRegValue,
+                               RRF_RT_REG_DWORD, nullptr, &light_mode,
+                               &light_mode_size);
+
+  if (result == ERROR_SUCCESS) {
+    BOOL enable_dark_mode = light_mode == 0;
+    DwmSetWindowAttribute(window, DWMWA_USE_IMMERSIVE_DARK_MODE,
+                          &enable_dark_mode, sizeof(enable_dark_mode));
+  }
+}