Revert "Gets the DPI for all awareness mode and older Windows versions (flutter#15951)"

This reverts commit d0bb4cd.

Author: NoamDev

shell/platform/windows/win32_dpi_helper.cc

@@ -4,8 +4,6 @@ namespace flutter {
 
 namespace {
 
-constexpr UINT kDefaultDpi = 96;
-
 template <typename T>
 bool AssignProcAddress(HMODULE comBaseModule, const char* name, T*& outProc) {
   outProc = reinterpret_cast<T*>(GetProcAddress(comBaseModule, name));
@@ -15,57 +13,60 @@ bool AssignProcAddress(HMODULE comBaseModule, const char* name, T*& outProc) {
 }  // namespace
 
 Win32DpiHelper::Win32DpiHelper() {
+  // TODO ensure that this helper works correctly on downlevel builds.
   user32_module_ = LoadLibraryA("User32.dll");
   if (user32_module_ == nullptr) {
     return;
   }
 
-  if (AssignProcAddress(user32_module_, "GetDpiForWindow",
-                        get_dpi_for_window_)) {
-    dpi_for_window_supported_ = true;
+  if (!AssignProcAddress(user32_module_, "EnableNonClientDpiScaling",
+                         enable_non_client_dpi_scaling_)) {
     return;
   }
 
-  shlib_module_ = LoadLibraryA("Shcore.dll");
-  if (shlib_module_ == nullptr) {
+  if (!AssignProcAddress(user32_module_, "GetDpiForWindow",
+                         get_dpi_for_window_)) {
     return;
   }
 
-  if (AssignProcAddress(shlib_module_, "GetDpiForMonitor",
-                        get_dpi_for_monitor_) &&
-      AssignProcAddress(user32_module_, "MonitorFromWindow",
-                        monitor_from_window_)) {
-    dpi_for_monitor_supported_ = true;
+  if (!AssignProcAddress(user32_module_, "SetProcessDpiAwarenessContext",
+                         set_process_dpi_awareness_context_)) {
+    return;
   }
+
+  permonitorv2_supported_ = true;
 }
 
 Win32DpiHelper::~Win32DpiHelper() {
   if (user32_module_ != nullptr) {
     FreeLibrary(user32_module_);
   }
-  if (shlib_module_ != nullptr) {
-    FreeLibrary(shlib_module_);
-  }
 }
 
-UINT Win32DpiHelper::GetDpi(HWND hwnd) {
-  // GetDpiForWindow returns the DPI for any awareness mode. If not available,
-  // fallback to a per monitor, system, or default DPI.
-  if (dpi_for_window_supported_) {
-    return get_dpi_for_window_(hwnd);
+bool Win32DpiHelper::IsPerMonitorV2Available() {
+  return permonitorv2_supported_;
+}
+
+BOOL Win32DpiHelper::EnableNonClientDpiScaling(HWND hwnd) {
+  if (!permonitorv2_supported_) {
+    return false;
   }
+  return enable_non_client_dpi_scaling_(hwnd);
+}
 
-  if (dpi_for_monitor_supported_) {
-    HMONITOR monitor = monitor_from_window_(hwnd, MONITOR_DEFAULTTONEAREST);
-    UINT dpi_x = 0, dpi_y = 0;
-    HRESULT result =
-        get_dpi_for_monitor_(monitor, MDT_EFFECTIVE_DPI, &dpi_x, &dpi_y);
-    return SUCCEEDED(result) ? dpi_x : kDefaultDpi;
+UINT Win32DpiHelper::GetDpiForWindow(HWND hwnd) {
+  if (!permonitorv2_supported_) {
+    return false;
   }
+  return get_dpi_for_window_(hwnd);
+}
 
-  HDC hdc = GetDC(hwnd);
-  UINT dpi = GetDeviceCaps(hdc, LOGPIXELSX);
-  ReleaseDC(hwnd, hdc);
-  return dpi;
+BOOL Win32DpiHelper::SetProcessDpiAwarenessContext(
+    DPI_AWARENESS_CONTEXT context) {
+  if (!permonitorv2_supported_) {
+    return false;
+  }
+  return set_process_dpi_awareness_context_(context);
 }
+
 }  // namespace flutter

shell/platform/windows/win32_dpi_helper.h

@@ -10,34 +10,38 @@
 
 namespace flutter {
 
-/// A helper class for abstracting various Windows DPI related functions across
-/// Windows OS versions.
+// A helper class for abstracting various Windows DPI related functions across
+// Windows OS versions.
 class Win32DpiHelper {
  public:
   Win32DpiHelper();
 
   ~Win32DpiHelper();
 
-  /// Returns the current DPI. Supports all DPI awareness modes, and is backward
-  /// compatible down to Windows Vista.
-  UINT GetDpi(HWND);
+  // Check if Windows Per Monitor V2 DPI scaling functionality is available on
+  // current system.
+  bool IsPerMonitorV2Available();
+
+  // Wrapper for OS functionality to turn on automatic window non-client scaling
+  BOOL EnableNonClientDpiScaling(HWND);
+
+  // Wrapper for OS functionality to return the DPI for |HWND|
+  UINT GetDpiForWindow(HWND);
+
+  // Sets the current process to a specified DPI awareness context.
+  BOOL SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT);
 
  private:
+  using EnableNonClientDpiScaling_ = BOOL __stdcall(HWND);
   using GetDpiForWindow_ = UINT __stdcall(HWND);
-  using GetDpiForMonitor_ = HRESULT __stdcall(HMONITOR hmonitor,
-                                              MONITOR_DPI_TYPE dpiType,
-                                              UINT* dpiX,
-                                              UINT* dpiY);
-  using MonitorFromWindow_ = HMONITOR __stdcall(HWND hwnd, DWORD dwFlags);
+  using SetProcessDpiAwarenessContext_ = BOOL __stdcall(DPI_AWARENESS_CONTEXT);
 
+  EnableNonClientDpiScaling_* enable_non_client_dpi_scaling_ = nullptr;
   GetDpiForWindow_* get_dpi_for_window_ = nullptr;
-  GetDpiForMonitor_* get_dpi_for_monitor_ = nullptr;
-  MonitorFromWindow_* monitor_from_window_ = nullptr;
+  SetProcessDpiAwarenessContext_* set_process_dpi_awareness_context_ = nullptr;
 
   HMODULE user32_module_ = nullptr;
-  HMODULE shlib_module_ = nullptr;
-  bool dpi_for_window_supported_ = false;
-  bool dpi_for_monitor_supported_ = false;
+  bool permonitorv2_supported_ = false;
 };
 
 }  // namespace flutter

shell/platform/windows/win32_window.cc

@@ -6,8 +6,16 @@
 
 namespace flutter {
 
-Win32Window::Win32Window() {}
-
+Win32Window::Win32Window() {
+  // Assume Windows 10 1703 or greater for DPI handling.  When running on a
+  // older release of Windows where this context doesn't exist, DPI calls will
+  // fail and Flutter rendering will be impacted until this is fixed.
+  // To handle downlevel correctly, dpi_helper must use the most recent DPI
+  // context available should be used: Windows 1703: Per-Monitor V2, 8.1:
+  // Per-Monitor V1, Windows 7: System See
+  // https://docs.microsoft.com/en-us/windows/win32/hidpi/high-dpi-desktop-application-development-on-windows
+  // for more information.
+}
 Win32Window::~Win32Window() {
   Destroy();
 }
@@ -18,7 +26,7 @@ void Win32Window::InitializeChild(const char* title,
   Destroy();
   std::wstring converted_title = NarrowToWide(title);
 
-  WNDCLASS window_class = RegisterWindowClass(converted_title);
+  WNDCLASS window_class = ResgisterWindowClass(converted_title);
 
   auto* result = CreateWindowEx(
       0, window_class.lpszClassName, converted_title.c_str(),
@@ -46,7 +54,7 @@ std::wstring Win32Window::NarrowToWide(const char* source) {
   return wideTitle;
 }
 
-WNDCLASS Win32Window::RegisterWindowClass(std::wstring& title) {
+WNDCLASS Win32Window::ResgisterWindowClass(std::wstring& title) {
   window_class_name_ = title;
 
   WNDCLASS window_class{};
@@ -74,7 +82,14 @@ LRESULT CALLBACK Win32Window::WndProc(HWND const window,
                      reinterpret_cast<LONG_PTR>(cs->lpCreateParams));
 
     auto that = static_cast<Win32Window*>(cs->lpCreateParams);
-    that->current_dpi_ = that->dpi_helper_->GetDpi(window);
+
+    // Since the application is running in Per-monitor V2 mode, turn on
+    // automatic titlebar scaling
+    BOOL result = that->dpi_helper_->EnableNonClientDpiScaling(window);
+    if (result != TRUE) {
+      OutputDebugString(L"Failed to enable non-client area autoscaling");
+    }
+    that->current_dpi_ = that->dpi_helper_->GetDpiForWindow(window);
     that->window_handle_ = window;
   } else if (Win32Window* that = GetThisFromHandle(window)) {
     return that->MessageHandler(window, message, wparam, lparam);
@@ -267,7 +282,7 @@ Win32Window::HandleDpiChange(HWND hwnd,
     // The DPI is only passed for DPI change messages on top level windows,
     // hence call function to get DPI if needed.
     if (uDpi == 0) {
-      uDpi = dpi_helper_->GetDpi(hwnd);
+      uDpi = dpi_helper_->GetDpiForWindow(hwnd);
     }
     current_dpi_ = uDpi;
     window->OnDpiScale(uDpi);

shell/platform/windows/win32_window.h

@@ -57,7 +57,7 @@ class Win32Window {
 
   // Registers a window class with default style attributes, cursor and
   // icon.
-  WNDCLASS RegisterWindowClass(std::wstring& title);
+  WNDCLASS ResgisterWindowClass(std::wstring& title);
 
   // OS callback called by message pump.  Handles the WM_NCCREATE message which
   // is passed when the non-client area is being created and enables automatic