Expose DPI helper functions for Runner apps to use

ci/licenses_golden/licenses_flutter

@@ -1116,6 +1116,8 @@ FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/flu
 FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/flutter_view_controller.h
 FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/plugin_registrar_windows.h
 FILE: ../../../flutter/shell/platform/windows/client_wrapper/plugin_registrar_windows_unittests.cc
+FILE: ../../../flutter/shell/platform/windows/dpi_utils.cc
+FILE: ../../../flutter/shell/platform/windows/dpi_utils.h
 FILE: ../../../flutter/shell/platform/windows/flutter_windows.cc
 FILE: ../../../flutter/shell/platform/windows/key_event_handler.cc
 FILE: ../../../flutter/shell/platform/windows/key_event_handler.h
@@ -1125,10 +1127,9 @@ FILE: ../../../flutter/shell/platform/windows/platform_handler.h
 FILE: ../../../flutter/shell/platform/windows/public/flutter_windows.h
 FILE: ../../../flutter/shell/platform/windows/text_input_plugin.cc
 FILE: ../../../flutter/shell/platform/windows/text_input_plugin.h
-FILE: ../../../flutter/shell/platform/windows/win32_dpi_helper.cc
-FILE: ../../../flutter/shell/platform/windows/win32_dpi_helper.h
 FILE: ../../../flutter/shell/platform/windows/win32_flutter_window.cc
 FILE: ../../../flutter/shell/platform/windows/win32_flutter_window.h
+FILE: ../../../flutter/shell/platform/windows/win32_flutter_window_unittests.cc
 FILE: ../../../flutter/shell/platform/windows/win32_task_runner.cc
 FILE: ../../../flutter/shell/platform/windows/win32_task_runner.h
 FILE: ../../../flutter/shell/platform/windows/win32_window.cc

shell/platform/windows/BUILD.gn

@@ -41,6 +41,8 @@ source_set("flutter_windows_source") {
   sources = [
     "angle_surface_manager.cc",
     "angle_surface_manager.h",
+    "dpi_utils.cc",
+    "dpi_utils.h",
     "flutter_windows.cc",
     "key_event_handler.cc",
     "key_event_handler.h",
@@ -49,8 +51,6 @@ source_set("flutter_windows_source") {
     "platform_handler.h",
     "text_input_plugin.cc",
     "text_input_plugin.h",
-    "win32_dpi_helper.cc",
-    "win32_dpi_helper.h",
     "win32_flutter_window.cc",
     "win32_flutter_window.h",
     "win32_task_runner.cc",
@@ -111,6 +111,9 @@ executable("flutter_windows_unittests") {
   sources = [
     "testing/win32_flutter_window_test.cc",
     "testing/win32_flutter_window_test.h",
+    "testing/win32_window_test.cc",
+    "testing/win32_window_test.h",
+    "win32_flutter_window_unittests.cc",
     "win32_window_unittests.cc",
   ]
 

shell/platform/windows/dpi_utils.cc

@@ -0,0 +1,127 @@
+#include "dpi_utils.h"
+
+namespace flutter {
+
+namespace {
+
+constexpr UINT kDefaultDpi = 96;
+
+// This is the MDT_EFFECTIVE_DPI value from MONITOR_DPI_TYPE, an enum declared
+// in ShellScalingApi.h. Replicating here to avoid importing the library
+// directly.
+constexpr UINT kEffectiveDpiMonitorType = 0;
+
+template <typename T>
+
+/// Retrieves a function |name| from a given |comBaseModule| into |outProc|.
+/// Returns a bool indicating whether the function was found.
+bool AssignProcAddress(HMODULE comBaseModule, const char* name, T*& outProc) {
+  outProc = reinterpret_cast<T*>(GetProcAddress(comBaseModule, name));
+  return *outProc != nullptr;
+}
+
+/// 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. If |hwnd| is nullptr, returns the DPI
+  /// for the primary monitor. Otherwise, returns the system's DPI.
+  UINT GetDpiForWindow(HWND);
+
+  /// Returns the DPI of a given monitor. Defaults to 96 if the API is not
+  /// available.
+  UINT GetDpiForMonitor(HMONITOR);
+
+ private:
+  using GetDpiForWindow_ = UINT __stdcall(HWND);
+  using GetDpiForMonitor_ = HRESULT __stdcall(HMONITOR hmonitor,
+                                              UINT dpiType,
+                                              UINT* dpiX,
+                                              UINT* dpiY);
+  using EnableNonClientDpiScaling_ = BOOL __stdcall(HWND hwnd);
+
+  GetDpiForWindow_* get_dpi_for_window_ = nullptr;
+  GetDpiForMonitor_* get_dpi_for_monitor_ = nullptr;
+  EnableNonClientDpiScaling_* enable_non_client_dpi_scaling_ = nullptr;
+
+  HMODULE user32_module_ = nullptr;
+  HMODULE shlib_module_ = nullptr;
+  bool dpi_for_window_supported_ = false;
+  bool dpi_for_monitor_supported_ = false;
+};
+
+Win32DpiHelper::Win32DpiHelper() {
+  user32_module_ = LoadLibraryA("User32.dll");
+  shlib_module_ = LoadLibraryA("Shcore.dll");
+  if (shlib_module_ == nullptr && user32_module_ == nullptr) {
+    return;
+  }
+
+  dpi_for_window_supported_ = (AssignProcAddress(
+      user32_module_, "GetDpiForWindow", get_dpi_for_window_));
+  dpi_for_monitor_supported_ = AssignProcAddress(
+      shlib_module_, "GetDpiForMonitor", get_dpi_for_monitor_);
+}
+
+Win32DpiHelper::~Win32DpiHelper() {
+  if (user32_module_ != nullptr) {
+    FreeLibrary(user32_module_);
+  }
+  if (shlib_module_ != nullptr) {
+    FreeLibrary(shlib_module_);
+  }
+}
+
+UINT Win32DpiHelper::GetDpiForWindow(HWND hwnd) {
+  // GetDpiForWindow returns the DPI for any awareness mode. If not available,
+  // or no |hwnd| is provided, fallback to a per monitor, system, or default
+  // DPI.
+  if (dpi_for_window_supported_ && hwnd != nullptr) {
+    return get_dpi_for_window_(hwnd);
+  }
+
+  if (dpi_for_monitor_supported_) {
+    HMONITOR monitor;
+    if (hwnd == nullptr) {
+      const POINT target_point = {static_cast<LONG>(0), static_cast<LONG>(0)};
+      monitor = MonitorFromPoint(target_point, MONITOR_DEFAULTTOPRIMARY);
+    } else {
+      monitor = MonitorFromWindow(hwnd, MONITOR_DEFAULTTOPRIMARY);
+    }
+    return GetDpiForMonitor(monitor);
+  }
+  HDC hdc = GetDC(hwnd);
+  UINT dpi = GetDeviceCaps(hdc, LOGPIXELSX);
+  ReleaseDC(hwnd, hdc);
+  return dpi;
+}
+
+UINT Win32DpiHelper::GetDpiForMonitor(HMONITOR monitor) {
+  if (dpi_for_monitor_supported_) {
+    UINT dpi_x = 0, dpi_y = 0;
+    HRESULT result =
+        get_dpi_for_monitor_(monitor, kEffectiveDpiMonitorType, &dpi_x, &dpi_y);
+    return SUCCEEDED(result) ? dpi_x : kDefaultDpi;
+  }
+  return kDefaultDpi;
+}
+
+Win32DpiHelper* GetHelper() {
+  static Win32DpiHelper* dpi_helper = new Win32DpiHelper();
+  return dpi_helper;
+}
+}  // namespace
+
+UINT GetDpiForHWND(HWND hwnd) {
+  return GetHelper()->GetDpiForWindow(hwnd);
+}
+
+UINT GetDpiForMonitor(HMONITOR monitor) {
+  return GetHelper()->GetDpiForMonitor(monitor);
+}
+}  // namespace flutter

shell/platform/windows/dpi_utils.h

@@ -0,0 +1,23 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "Windows.h"
+
+#ifndef FLUTTER_SHELL_PLATFORM_WINDOWS_DPI_UTILS_H_
+#define FLUTTER_SHELL_PLATFORM_WINDOWS_DPI_UTILS_H_
+
+namespace flutter {
+
+/// Returns the current DPI. Supports all DPI awareness modes, and is backward
+/// compatible down to Windows Vista. If |hwnd| is nullptr, returns the DPI for
+/// the primary monitor. Otherwise, returns the system's DPI.
+UINT GetDpiForHWND(HWND hwnd);
+
+/// Returns the DPI of a given monitor. Defaults to 96 if the API is not
+/// available.
+UINT GetDpiForMonitor(HMONITOR monitor);
+
+}  // namespace flutter
+
+#endif  // FLUTTER_SHELL_PLATFORM_WINDOWS_DPI_UTILS_H_

shell/platform/windows/flutter_windows.cc

@@ -15,6 +15,7 @@
 #include "flutter/shell/platform/common/cpp/client_wrapper/include/flutter/plugin_registrar.h"
 #include "flutter/shell/platform/common/cpp/incoming_message_dispatcher.h"
 #include "flutter/shell/platform/embedder/embedder.h"
+#include "flutter/shell/platform/windows/dpi_utils.h"
 #include "flutter/shell/platform/windows/key_event_handler.h"
 #include "flutter/shell/platform/windows/keyboard_hook_handler.h"
 #include "flutter/shell/platform/windows/platform_handler.h"
@@ -182,6 +183,14 @@ HWND FlutterDesktopViewGetHWND(FlutterDesktopViewRef view) {
   return view->window->GetWindowHandle();
 }
 
+UINT FlutterDesktopGetDpiForHWND(HWND hwnd) {
+  return flutter::GetDpiForHWND(hwnd);
+}
+
+UINT FlutterDesktopGetDpiForMonitor(HMONITOR monitor) {
+  return flutter::GetDpiForMonitor(monitor);
+}
+
 FlutterDesktopEngineRef FlutterDesktopRunEngine(const char* assets_path,
                                                 const char* icu_data_path,
                                                 const char** arguments,

shell/platform/windows/public/flutter_windows.h

@@ -77,6 +77,15 @@ FlutterDesktopProcessMessages(FlutterDesktopViewControllerRef controller);
 // Return backing HWND for manipulation in host application.
 FLUTTER_EXPORT HWND FlutterDesktopViewGetHWND(FlutterDesktopViewRef view);
 
+// Gets the DPI for a given |hwnd|, depending on the supported APIs per
+// windows version and DPI awareness mode. If nullptr is passed, returns the DPI
+// of the primary monitor.
+FLUTTER_EXPORT UINT FlutterDesktopGetDpiForHWND(HWND hwnd);
+
+// Gets the DPI for a given |monitor|. If the API is not available, a default
+// DPI of 96 is returned.
+FLUTTER_EXPORT UINT FlutterDesktopGetDpiForMonitor(HMONITOR monitor);
+
 // Runs an instance of a headless Flutter engine.
 //
 // The |assets_path| is the path to the flutter_assets folder for the Flutter

shell/platform/windows/testing/win32_window_test.cc

@@ -0,0 +1,35 @@
+#include "flutter/shell/platform/windows/testing/win32_window_test.h"
+
+namespace flutter {
+namespace testing {
+
+Win32WindowTest::Win32WindowTest() : Win32Window(){};
+
+Win32WindowTest::~Win32WindowTest() = default;
+
+void Win32WindowTest::OnDpiScale(unsigned int dpi){};
+
+void Win32WindowTest::OnResize(unsigned int width, unsigned int height) {}
+
+void Win32WindowTest::OnPointerMove(double x, double y) {}
+
+void Win32WindowTest::OnPointerDown(double x, double y, UINT button) {}
+
+void Win32WindowTest::OnPointerUp(double x, double y, UINT button) {}
+
+void Win32WindowTest::OnPointerLeave() {}
+
+void Win32WindowTest::OnChar(char32_t code_point) {}
+
+void Win32WindowTest::OnKey(int key, int scancode, int action, int mods) {}
+
+void Win32WindowTest::OnScroll(double delta_x, double delta_y) {}
+
+void Win32WindowTest::OnFontChange() {}
+
+UINT Win32WindowTest::GetDpi() {
+  return GetCurrentDPI();
+}
+
+}  // namespace testing
+}  // namespace flutter

shell/platform/windows/testing/win32_window_test.h

@@ -0,0 +1,56 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <windowsx.h>
+
+#include "flutter/fml/macros.h"
+#include "flutter/shell/platform/windows/win32_window.h"
+
+namespace flutter {
+namespace testing {
+
+class Win32WindowTest : public Win32Window {
+ public:
+  Win32WindowTest();
+  ~Win32WindowTest();
+
+  // Wrapper for GetCurrentDPI() which is a protected method.
+  UINT GetDpi();
+
+  // |Win32Window|
+  void OnDpiScale(unsigned int dpi) override;
+
+  // |Win32Window|
+  void OnResize(unsigned int width, unsigned int height) override;
+
+  // |Win32Window|
+  void OnPointerMove(double x, double y) override;
+
+  // |Win32Window|
+  void OnPointerDown(double x, double y, UINT button) override;
+
+  // |Win32Window|
+  void OnPointerUp(double x, double y, UINT button) override;
+
+  // |Win32Window|
+  void OnPointerLeave() override;
+
+  // |Win32Window|
+  void OnChar(char32_t code_point) override;
+
+  // |Win32Window|
+  void OnKey(int key, int scancode, int action, int mods) override;
+
+  // |Win32Window|
+  void OnScroll(double delta_x, double delta_y) override;
+
+  // |Win32Window|
+  void OnFontChange() override;
+
+ private:
+  FML_DISALLOW_COPY_AND_ASSIGN(Win32WindowTest);
+};
+
+}  // namespace testing
+}  // namespace flutter