Implement cursor support for Windows (#19459)

Implements the basic engine support for Windows for
https://github.com/flutter/flutter/issues/31952

ci/licenses_golden/licenses_flutter

@@ -1310,6 +1310,8 @@ 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/cursor_handler.cc
+FILE: ../../../flutter/shell/platform/windows/cursor_handler.h
 FILE: ../../../flutter/shell/platform/windows/flutter_windows.cc
 FILE: ../../../flutter/shell/platform/windows/flutter_windows_view.cc
 FILE: ../../../flutter/shell/platform/windows/flutter_windows_view.h

shell/platform/windows/BUILD.gn

@@ -41,6 +41,8 @@ source_set("flutter_windows_source") {
   sources = [
     "angle_surface_manager.cc",
     "angle_surface_manager.h",
+    "cursor_handler.cc",
+    "cursor_handler.h",
     "flutter_windows.cc",
     "flutter_windows_view.cc",
     "flutter_windows_view.h",

shell/platform/windows/cursor_handler.cc

+// 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 "flutter/shell/platform/windows/cursor_handler.h"
+
+#include <windows.h>
+
+#include "flutter/shell/platform/common/cpp/client_wrapper/include/flutter/standard_method_codec.h"
+
+static constexpr char kChannelName[] = "flutter/mousecursor";
+
+static constexpr char kActivateSystemCursorMethod[] = "activateSystemCursor";
+
+static constexpr char kKindKey[] = "kind";
+
+namespace flutter {
+
+CursorHandler::CursorHandler(flutter::BinaryMessenger* messenger,
+                             WindowBindingHandler* delegate)
+    : channel_(std::make_unique<flutter::MethodChannel<EncodableValue>>(
+          messenger,
+          kChannelName,
+          &flutter::StandardMethodCodec::GetInstance())),
+      delegate_(delegate) {
+  channel_->SetMethodCallHandler(
+      [this](const flutter::MethodCall<EncodableValue>& call,
+             std::unique_ptr<flutter::MethodResult<EncodableValue>> result) {
+        HandleMethodCall(call, std::move(result));
+      });
+}
+
+void CursorHandler::HandleMethodCall(
+    const flutter::MethodCall<EncodableValue>& method_call,
+    std::unique_ptr<flutter::MethodResult<EncodableValue>> result) {
+  const std::string& method = method_call.method_name();
+  if (method.compare(kActivateSystemCursorMethod) == 0) {
+    const flutter::EncodableMap& arguments =
+        method_call.arguments()->MapValue();
+    auto kind_iter = arguments.find(EncodableValue(kKindKey));
+    if (kind_iter == arguments.end()) {
+      result->Error("Argument error",
+                    "Missing argument while trying to activate system cursor");
+    }
+    const std::string& kind = kind_iter->second.StringValue();
+    delegate_->UpdateFlutterCursor(kind);
+    result->Success();
+  } else {
+    result->NotImplemented();
+  }
+}
+
+}  // namespace flutter

shell/platform/windows/cursor_handler.h

+// 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.
+
+#ifndef FLUTTER_SHELL_PLATFORM_WINDOWS_CURSOR_HANDLER_H_
+#define FLUTTER_SHELL_PLATFORM_WINDOWS_CURSOR_HANDLER_H_
+
+#include "flutter/shell/platform/common/cpp/client_wrapper/include/flutter/binary_messenger.h"
+#include "flutter/shell/platform/common/cpp/client_wrapper/include/flutter/encodable_value.h"
+#include "flutter/shell/platform/common/cpp/client_wrapper/include/flutter/method_channel.h"
+#include "flutter/shell/platform/windows/public/flutter_windows.h"
+#include "flutter/shell/platform/windows/window_binding_handler.h"
+
+namespace flutter {
+
+// Handler for the cursor system channel.
+class CursorHandler {
+ public:
+  explicit CursorHandler(flutter::BinaryMessenger* messenger,
+                         WindowBindingHandler* delegate);
+
+ private:
+  // Called when a method is called on |channel_|;
+  void HandleMethodCall(
+      const flutter::MethodCall<EncodableValue>& method_call,
+      std::unique_ptr<flutter::MethodResult<EncodableValue>> result);
+
+  // The MethodChannel used for communication with the Flutter engine.
+  std::unique_ptr<flutter::MethodChannel<EncodableValue>> channel_;
+
+  // The delegate for cursor updates.
+  WindowBindingHandler* delegate_;
+};
+
+}  // namespace flutter
+
+#endif  // FLUTTER_SHELL_PLATFORM_WINDOWS_CURSOR_HANDLER_H_

shell/platform/windows/flutter_windows.cc

@@ -20,9 +20,6 @@
 #include "flutter/shell/platform/common/cpp/path_utils.h"
 #include "flutter/shell/platform/embedder/embedder.h"
 #include "flutter/shell/platform/windows/flutter_windows_view.h"
-#include "flutter/shell/platform/windows/key_event_handler.h"
-#include "flutter/shell/platform/windows/keyboard_hook_handler.h"
-#include "flutter/shell/platform/windows/text_input_plugin.h"
 #include "flutter/shell/platform/windows/win32_dpi_utils.h"
 #include "flutter/shell/platform/windows/win32_flutter_window.h"
 #include "flutter/shell/platform/windows/win32_platform_handler.h"

shell/platform/windows/flutter_windows_view.cc

@@ -65,6 +65,8 @@ void FlutterWindowsView::SetState(FLUTTER_API_SYMBOL(FlutterEngine) eng) {
       std::make_unique<flutter::TextInputPlugin>(internal_plugin_messenger));
   platform_handler_ = std::make_unique<flutter::PlatformHandler>(
       internal_plugin_messenger, this);
+  cursor_handler_ = std::make_unique<flutter::CursorHandler>(
+      internal_plugin_messenger, binding_handler_.get());
 
   PhysicalWindowBounds bounds = binding_handler_->GetPhysicalWindowBounds();
 

shell/platform/windows/flutter_windows_view.h

@@ -14,6 +14,7 @@
 #include "flutter/shell/platform/common/cpp/incoming_message_dispatcher.h"
 #include "flutter/shell/platform/embedder/embedder.h"
 #include "flutter/shell/platform/windows/angle_surface_manager.h"
+#include "flutter/shell/platform/windows/cursor_handler.h"
 #include "flutter/shell/platform/windows/key_event_handler.h"
 #include "flutter/shell/platform/windows/keyboard_hook_handler.h"
 #include "flutter/shell/platform/windows/public/flutter_windows.h"
@@ -213,6 +214,9 @@ class FlutterWindowsView : public WindowBindingHandlerDelegate {
   // Handler for the flutter/platform channel.
   std::unique_ptr<flutter::PlatformHandler> platform_handler_;
 
+  // Handler for cursor events.
+  std::unique_ptr<flutter::CursorHandler> cursor_handler_;
+
   // Currently configured WindowBindingHandler for view.
   std::unique_ptr<flutter::WindowBindingHandler> binding_handler_;
 };

shell/platform/windows/testing/win32_window_test.cc

@@ -19,6 +19,8 @@ void Win32WindowTest::OnPointerUp(double x, double y, UINT button) {}
 
 void Win32WindowTest::OnPointerLeave() {}
 
+void Win32WindowTest::OnSetCursor() {}
+
 void Win32WindowTest::OnText(const std::u16string& text) {}
 
 void Win32WindowTest::OnKey(int key,

shell/platform/windows/testing/win32_window_test.h

@@ -41,6 +41,9 @@ class Win32WindowTest : public Win32Window {
   // |Win32Window|
   void OnPointerLeave() override;
 
+  // |Win32Window|
+  void OnSetCursor() override;
+
   // |Win32Window|
   void OnText(const std::u16string& text) override;
 

shell/platform/windows/win32_flutter_window.cc

 #include "flutter/shell/platform/windows/win32_flutter_window.h"
 
 #include <chrono>
+#include <map>
 
 namespace flutter {
 
+namespace {
+
 // The Windows DPI system is based on this
 // constant for machines running at 100% scaling.
 constexpr int base_dpi = 96;
@@ -12,9 +15,33 @@ constexpr int base_dpi = 96;
 // arbitrarily to get something that feels reasonable.
 constexpr int kScrollOffsetMultiplier = 20;
 
+// Maps a Flutter cursor name to an HCURSOR.
+//
+// Returns the arrow cursor for unknown constants.
+static HCURSOR GetCursorByName(const std::string& cursor_name) {
+  static auto* cursors = new std::map<std::string, const wchar_t*>{
+      {"none", nullptr},
+      {"basic", IDC_ARROW},
+      {"click", IDC_HAND},
+      {"text", IDC_IBEAM},
+      {"forbidden", IDC_NO},
+      {"horizontalDoubleArrow", IDC_SIZEWE},
+      {"verticalDoubleArrow", IDC_SIZENS},
+  };
+  const wchar_t* idc_name = IDC_ARROW;
+  auto it = cursors->find(cursor_name);
+  if (it != cursors->end()) {
+    idc_name = it->second;
+  }
+  return ::LoadCursor(nullptr, idc_name);
+}
+
+}  // namespace
+
 Win32FlutterWindow::Win32FlutterWindow(int width, int height)
     : binding_handler_delegate_(nullptr) {
   Win32Window::InitializeChild("FLUTTERVIEW", width, height);
+  current_cursor_ = ::LoadCursor(nullptr, IDC_ARROW);
 }
 
 Win32FlutterWindow::~Win32FlutterWindow() {}
@@ -35,6 +62,10 @@ PhysicalWindowBounds Win32FlutterWindow::GetPhysicalWindowBounds() {
   return {GetCurrentWidth(), GetCurrentHeight()};
 }
 
+void Win32FlutterWindow::UpdateFlutterCursor(const std::string& cursor_name) {
+  current_cursor_ = GetCursorByName(cursor_name);
+}
+
 // Translates button codes from Win32 API to FlutterPointerMouseButtons.
 static uint64_t ConvertWinButtonToFlutterButton(UINT button) {
   switch (button) {
@@ -90,6 +121,10 @@ void Win32FlutterWindow::OnPointerLeave() {
   binding_handler_delegate_->OnPointerLeave();
 }
 
+void Win32FlutterWindow::OnSetCursor() {
+  ::SetCursor(current_cursor_);
+}
+
 void Win32FlutterWindow::OnText(const std::u16string& text) {
   binding_handler_delegate_->OnText(text);
 }

shell/platform/windows/win32_flutter_window.h

@@ -12,7 +12,6 @@
 #include <vector>
 
 #include "flutter/shell/platform/embedder/embedder.h"
-
 #include "flutter/shell/platform/windows/flutter_windows_view.h"
 #include "flutter/shell/platform/windows/win32_window.h"
 #include "flutter/shell/platform/windows/window_binding_handler.h"
@@ -48,6 +47,9 @@ class Win32FlutterWindow : public Win32Window, public WindowBindingHandler {
   // |Win32Window|
   void OnPointerLeave() override;
 
+  // |Win32Window|
+  void OnSetCursor() override;
+
   // |Win32Window|
   void OnText(const std::u16string& text) override;
 
@@ -72,9 +74,16 @@ class Win32FlutterWindow : public Win32Window, public WindowBindingHandler {
   // |FlutterWindowBindingHandler|
   PhysicalWindowBounds GetPhysicalWindowBounds() override;
 
+  // |FlutterWindowBindingHandler|
+  void UpdateFlutterCursor(const std::string& cursor_name) override;
+
+ private:
   // A pointer to a FlutterWindowsView that can be used to update engine
   // windowing and input state.
   WindowBindingHandlerDelegate* binding_handler_delegate_;
+
+  // The last cursor set by Flutter. Defaults to the arrow cursor.
+  HCURSOR current_cursor_;
 };
 
 }  // namespace flutter

shell/platform/windows/win32_window.cc

@@ -150,6 +150,14 @@ Win32Window::MessageHandler(HWND hwnd,
         // detected again.
         tracking_mouse_leave_ = false;
         break;
+      case WM_SETCURSOR: {
+        UINT hit_test_result = LOWORD(lparam);
+        if (hit_test_result == HTCLIENT) {
+          window->OnSetCursor();
+          return TRUE;
+        }
+        break;
+      }
       case WM_LBUTTONDOWN:
       case WM_RBUTTONDOWN:
       case WM_MBUTTONDOWN:

shell/platform/windows/win32_window.h

@@ -86,6 +86,9 @@ class Win32Window {
   // Called when the mouse leaves the window.
   virtual void OnPointerLeave() = 0;
 
+  // Called when the cursor should be set for the client area.
+  virtual void OnSetCursor() = 0;
+
   // Called when text input occurs.
   virtual void OnText(const std::u16string& text) = 0;
 

shell/platform/windows/window_binding_handler.h

@@ -5,13 +5,12 @@
 #ifndef FLUTTER_SHELL_PLATFORM_WINDOWS_WINDOW_BINDING_HANDLER_H_
 #define FLUTTER_SHELL_PLATFORM_WINDOWS_WINDOW_BINDING_HANDLER_H_
 
-#include "flutter/shell/platform/windows/public/flutter_windows.h"
+#include <windows.h>
 
 #include <string>
 #include <variant>
 
-#include <windows.h>
-
+#include "flutter/shell/platform/windows/public/flutter_windows.h"
 #include "flutter/shell/platform/windows/window_binding_handler_delegate.h"
 
 namespace flutter {
@@ -45,6 +44,10 @@ class WindowBindingHandler {
 
   // Returns the bounds of the backing window in physical pixels.
   virtual PhysicalWindowBounds GetPhysicalWindowBounds() = 0;
+
+  // Sets the cursor that should be used when the mouse is over the Flutter
+  // content. See mouse_cursor.dart for the values and meanings of cursor_name.
+  virtual void UpdateFlutterCursor(const std::string& cursor_name) = 0;
 };
 
 }  // namespace flutter