Add support for IME-based text input on Windows

ci/licenses_golden/licenses_flutter

@@ -1497,6 +1497,8 @@ FILE: ../../../flutter/shell/platform/windows/task_runner_win32.cc
 FILE: ../../../flutter/shell/platform/windows/task_runner_win32.h
 FILE: ../../../flutter/shell/platform/windows/task_runner_winuwp.cc
 FILE: ../../../flutter/shell/platform/windows/task_runner_winuwp.h
+FILE: ../../../flutter/shell/platform/windows/text_input_manager.cc
+FILE: ../../../flutter/shell/platform/windows/text_input_manager.h
 FILE: ../../../flutter/shell/platform/windows/text_input_plugin.cc
 FILE: ../../../flutter/shell/platform/windows/text_input_plugin.h
 FILE: ../../../flutter/shell/platform/windows/text_input_plugin_delegate.h

shell/platform/common/cpp/text_input_model.cc

@@ -67,11 +67,7 @@ void TextInputModel::BeginComposing() {
   composing_range_ = TextRange(selection_.start());
 }
 
-void TextInputModel::UpdateComposingText(const std::string& composing_text) {
-  std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t>
-      utf16_converter;
-  std::u16string text = utf16_converter.from_bytes(composing_text);
-
+void TextInputModel::UpdateComposingText(const std::u16string& text) {
   // Preserve selection if we get a no-op update to the composing region.
   if (text.length() == 0 && composing_range_.collapsed()) {
     return;
@@ -82,6 +78,12 @@ void TextInputModel::UpdateComposingText(const std::string& composing_text) {
   selection_ = TextRange(composing_range_.end());
 }
 
+void TextInputModel::UpdateComposingText(const std::string& text) {
+  std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t>
+      utf16_converter;
+  UpdateComposingText(utf16_converter.from_bytes(text));
+}
+
 void TextInputModel::CommitComposing() {
   // Preserve selection if no composing text was entered.
   if (composing_range_.collapsed()) {

shell/platform/common/cpp/text_input_model.h

@@ -46,13 +46,21 @@ class TextInputModel {
   // are restricted to the composing range.
   void BeginComposing();
 
-  // Replaces the composing range with new text.
+  // Replaces the composing range with new UTF-16 text.
   //
   // If a selection of non-zero length exists, it is deleted if the composing
   // text is non-empty. The composing range is adjusted to the length of
-  // |composing_text| and the selection base and offset are set to the end of
-  // the composing range.
-  void UpdateComposingText(const std::string& composing_text);
+  // |text| and the selection base and offset are set to the end of the
+  // composing range.
+  void UpdateComposingText(const std::u16string& text);
+
+  // Replaces the composing range with new UTF-8 text.
+  //
+  // If a selection of non-zero length exists, it is deleted if the composing
+  // text is non-empty. The composing range is adjusted to the length of
+  // |text| and the selection base and offset are set to the end of the
+  // composing range.
+  void UpdateComposingText(const std::string& text);
 
   // Commits composing range to the string.
   //

shell/platform/windows/BUILD.gn

@@ -68,6 +68,8 @@ source_set("flutter_windows_source") {
     "string_conversion.h",
     "system_utils.h",
     "task_runner.h",
+    "text_input_manager.cc",
+    "text_input_manager.h",
     "text_input_plugin.cc",
     "text_input_plugin.h",
     "window_binding_handler.h",
@@ -103,7 +105,10 @@ source_set("flutter_windows_source") {
       "win32_window_proc_delegate_manager.h",
     ]
 
-    libs = [ "dwmapi.lib" ]
+    libs = [
+      "dwmapi.lib",
+      "imm32.lib",
+    ]
   }
 
   configs += [

shell/platform/windows/flutter_windows_view.cc

@@ -137,6 +137,19 @@ bool FlutterWindowsView::OnKey(int key,
   return SendKey(key, scancode, action, character, extended);
 }
 
+void FlutterWindowsView::OnComposeBegin() {
+  SendComposeBegin();
+}
+
+void FlutterWindowsView::OnComposeEnd() {
+  SendComposeEnd();
+}
+
+void FlutterWindowsView::OnComposeChange(const std::u16string& text,
+                                         int cursor_pos) {
+  SendComposeChange(text, cursor_pos);
+}
+
 void FlutterWindowsView::OnScroll(double x,
                                   double y,
                                   double delta_x,
@@ -240,6 +253,25 @@ bool FlutterWindowsView::SendKey(int key,
   return false;
 }
 
+void FlutterWindowsView::SendComposeBegin() {
+  for (const auto& handler : keyboard_hook_handlers_) {
+    handler->ComposeBeginHook();
+  }
+}
+
+void FlutterWindowsView::SendComposeEnd() {
+  for (const auto& handler : keyboard_hook_handlers_) {
+    handler->ComposeEndHook();
+  }
+}
+
+void FlutterWindowsView::SendComposeChange(const std::u16string& text,
+                                           int cursor_pos) {
+  for (const auto& handler : keyboard_hook_handlers_) {
+    handler->ComposeChangeHook(text, cursor_pos);
+  }
+}
+
 void FlutterWindowsView::SendScroll(double x,
                                     double y,
                                     double delta_x,

shell/platform/windows/flutter_windows_view.h

@@ -106,6 +106,15 @@ class FlutterWindowsView : public WindowBindingHandlerDelegate,
              char32_t character,
              bool extended) override;
 
+  // |WindowBindingHandlerDelegate|
+  void OnComposeBegin() override;
+
+  // |WindowBindingHandlerDelegate|
+  void OnComposeEnd() override;
+
+  // |WindowBindingHandlerDelegate|
+  void OnComposeChange(const std::u16string& text, int cursor_pos) override;
+
   // |WindowBindingHandlerDelegate|
   void OnScroll(double x,
                 double y,
@@ -185,6 +194,24 @@ class FlutterWindowsView : public WindowBindingHandlerDelegate,
                char32_t character,
                bool extended);
 
+  // Reports an IME compose begin event.
+  //
+  // Triggered when the user begins editing composing text using a multi-step
+  // input method such as in CJK text input.
+  void SendComposeBegin();
+
+  // Reports an IME compose end event.
+  //
+  // Triggered when the user commits the composing text while using a multi-step
+  // input method such as in CJK text input.
+  void SendComposeEnd();
+
+  // Reports an IME composing region change event.
+  //
+  // Triggered when the user edits the composing text while using a multi-step
+  // input method such as in CJK text input.
+  void SendComposeChange(const std::u16string& text, int cursor_pos);
+
   // Reports scroll wheel events to Flutter engine.
   void SendScroll(double x,
                   double y,

shell/platform/windows/key_event_handler.cc

@@ -243,4 +243,17 @@ bool KeyEventHandler::KeyboardHook(FlutterWindowsView* view,
   return true;
 }
 
+void KeyEventHandler::ComposeBeginHook() {
+  // Ignore.
+}
+
+void KeyEventHandler::ComposeEndHook() {
+  // Ignore.
+}
+
+void KeyEventHandler::ComposeChangeHook(const std::u16string& text,
+                                        int cursor_pos) {
+  // Ignore.
+}
+
 }  // namespace flutter

shell/platform/windows/key_event_handler.h

@@ -44,6 +44,15 @@ class KeyEventHandler : public KeyboardHookHandler {
   void TextHook(FlutterWindowsView* window,
                 const std::u16string& text) override;
 
+  // |KeyboardHookHandler|
+  void ComposeBeginHook() override;
+
+  // |KeyboardHookHandler|
+  void ComposeEndHook() override;
+
+  // |KeyboardHookHandler|
+  void ComposeChangeHook(const std::u16string& text, int cursor_pos) override;
+
  private:
   KEYBDINPUT* FindPendingEvent(uint64_t id);
   void RemovePendingEvent(uint64_t id);

shell/platform/windows/keyboard_hook_handler.h

@@ -32,6 +32,25 @@ class KeyboardHookHandler {
   // A function for hooking into Unicode text input.
   virtual void TextHook(FlutterWindowsView* view,
                         const std::u16string& text) = 0;
+
+  // Handler for IME compose begin events.
+  //
+  // Triggered when the user begins editing composing text using a multi-step
+  // input method such as in CJK text input.
+  virtual void ComposeBeginHook() = 0;
+
+  // Handler for IME compose end events.
+  //
+  // Triggered when the user commits the composing text while using a multi-step
+  // input method such as in CJK text input.
+  virtual void ComposeEndHook() = 0;
+
+  // Handler for IME compose change events.
+  //
+  // Triggered when the user edits the composing text while using a multi-step
+  // input method such as in CJK text input.
+  virtual void ComposeChangeHook(const std::u16string& text,
+                                 int cursor_pos) = 0;
 };
 
 }  // namespace flutter

shell/platform/windows/testing/mock_win32_window.h

@@ -41,6 +41,9 @@ class MockWin32Window : public Win32Window {
   MOCK_METHOD1(OnText, void(const std::u16string&));
   MOCK_METHOD5(OnKey, bool(int, int, int, char32_t, bool));
   MOCK_METHOD2(OnScroll, void(double, double));
+  MOCK_METHOD0(OnComposeBegin, void());
+  MOCK_METHOD0(OnComposeEnd, void());
+  MOCK_METHOD2(OnComposeChange, void(const std::u16string&, int));
 };
 
 }  // namespace testing

shell/platform/windows/text_input_manager.cc

@@ -0,0 +1,139 @@
+// 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.
+
+// 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/text_input_manager.h"
+
+#include <imm.h>
+
+#include <memory>
+
+namespace flutter {
+
+void TextInputManager::SetWindowHandle(HWND window_handle) {
+  window_handle_ = window_handle;
+}
+
+void TextInputManager::CreateImeWindow() {
+  if (window_handle_ == nullptr) {
+    return;
+  }
+
+  // Some IMEs ignore calls to ::ImmSetCandidateWindow() and use the position of
+  // the current system caret instead via ::GetCaretPos(). In order to behave
+  // as expected with these IMEs, we create a temporary system caret.
+  if (!ime_active_) {
+    ::CreateCaret(window_handle_, nullptr, 1, 1);
+  }
+  ime_active_ = true;
+
+  // Set the position of the IME windows.
+  UpdateImeWindow();
+}
+
+void TextInputManager::DestroyImeWindow() {
+  if (window_handle_ == nullptr) {
+    return;
+  }
+
+  // Destroy the system caret created in CreateImeWindow().
+  if (ime_active_) {
+    ::DestroyCaret();
+  }
+  ime_active_ = false;
+}
+
+void TextInputManager::UpdateImeWindow() {
+  if (window_handle_ == nullptr) {
+    return;
+  }
+
+  HIMC imm_context = ::ImmGetContext(window_handle_);
+  if (imm_context) {
+    MoveImeWindow(imm_context);
+    ::ImmReleaseContext(window_handle_, imm_context);
+  }
+}
+
+void TextInputManager::UpdateCaretRect(const Rect& rect) {
+  caret_rect_ = rect;
+
+  if (window_handle_ == nullptr) {
+    return;
+  }
+
+  // TODO(cbracken): wrap these in an RAII container.
+  HIMC imm_context = ::ImmGetContext(window_handle_);
+  if (imm_context) {
+    MoveImeWindow(imm_context);
+    ::ImmReleaseContext(window_handle_, imm_context);
+  }
+}
+
+long TextInputManager::GetComposingCursorPosition() const {
+  if (window_handle_ == nullptr) {
+    return false;
+  }
+
+  HIMC imm_context = ::ImmGetContext(window_handle_);
+  if (imm_context) {
+    // Read the cursor position within the composing string.
+    const int pos =
+        ImmGetCompositionStringW(imm_context, GCS_CURSORPOS, nullptr, 0);
+    ::ImmReleaseContext(window_handle_, imm_context);
+    return pos;
+  }
+  return -1;
+}
+
+std::optional<std::u16string> TextInputManager::GetComposingString() const {
+  return GetString(GCS_COMPSTR);
+}
+
+std::optional<std::u16string> TextInputManager::GetResultString() const {
+  return GetString(GCS_RESULTSTR);
+}
+
+std::optional<std::u16string> TextInputManager::GetString(int type) const {
+  if (window_handle_ == nullptr || !ime_active_) {
+    return std::nullopt;
+  }
+  HIMC imm_context = ::ImmGetContext(window_handle_);
+  if (imm_context) {
+    // Read the composing string length.
+    const long compose_bytes =
+        ::ImmGetCompositionString(imm_context, type, nullptr, 0);
+    const long compose_length = compose_bytes / sizeof(wchar_t);
+    if (compose_length <= 0) {
+      ::ImmReleaseContext(window_handle_, imm_context);
+      return std::nullopt;
+    }
+
+    std::u16string text(compose_length, '\0');
+    ::ImmGetCompositionString(imm_context, type, &text[0], compose_bytes);
+    ::ImmReleaseContext(window_handle_, imm_context);
+    return text;
+  }
+  return std::nullopt;
+}
+
+void TextInputManager::MoveImeWindow(HIMC imm_context) {
+  if (GetFocus() != window_handle_ || !ime_active_) {
+    return;
+  }
+  LONG x = caret_rect_.left();
+  LONG y = caret_rect_.top();
+  ::SetCaretPos(x, y);
+
+  COMPOSITIONFORM cf = {CFS_POINT, {x, y}};
+  ::ImmSetCompositionWindow(imm_context, &cf);
+
+  CANDIDATEFORM candidate_form = {0, CFS_CANDIDATEPOS, {x, y}, {0, 0, 0, 0}};
+  ::ImmSetCandidateWindow(imm_context, &candidate_form);
+}
+
+}  // namespace flutter