Flutter Windows Embedder
keyboard_manager.cc
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1 // Copyright 2013 The Flutter Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #include <memory>
6 #include <string>
7 
8 #include "flutter/fml/logging.h"
11 
12 namespace flutter {
13 
14 namespace {
15 
16 // The maximum number of pending events to keep before
17 // emitting a warning on the console about unhandled events.
18 constexpr int kMaxPendingEvents = 1000;
19 
20 // Returns true if this key is an AltRight key down event.
21 //
22 // This is used to resolve an issue where an AltGr press causes CtrlLeft to hang
23 // when pressed, as reported in https://github.com/flutter/flutter/issues/78005.
24 //
25 // When AltGr is pressed (in a supporting layout such as Spanish), Win32 first
26 // fires a fake CtrlLeft down event, then an AltRight down event.
27 // This is significant because this fake CtrlLeft down event will not be paired
28 // with a up event, which is fine until Flutter redispatches the CtrlDown
29 // event, which Win32 then interprets as a real event, leaving both Win32 and
30 // the Flutter framework thinking that CtrlLeft is still pressed.
31 //
32 // To resolve this, Flutter recognizes this fake CtrlLeft down event using the
33 // following AltRight down event. Flutter then forges a CtrlLeft key up event
34 // immediately after the corresponding AltRight key up event.
35 //
36 // One catch is that it is impossible to distinguish the fake CtrlLeft down
37 // from a normal CtrlLeft down (followed by a AltRight down), since they
38 // contain the exactly same information, including the GetKeyState result.
39 // Fortunately, this will require the two events to occur *really* close, which
40 // would be rare, and a misrecognition would only cause a minor consequence
41 // where the CtrlLeft is released early; the later, real, CtrlLeft up event will
42 // be ignored.
43 bool IsKeyDownAltRight(int action, int virtual_key, bool extended) {
44  return virtual_key == VK_RMENU && extended &&
45  (action == WM_KEYDOWN || action == WM_SYSKEYDOWN);
46 }
47 
48 // Returns true if this key is a key up event of AltRight.
49 //
50 // This is used to assist a corner case described in |IsKeyDownAltRight|.
51 bool IsKeyUpAltRight(int action, int virtual_key, bool extended) {
52  return virtual_key == VK_RMENU && extended &&
53  (action == WM_KEYUP || action == WM_SYSKEYUP);
54 }
55 
56 // Returns true if this key is a key down event of CtrlLeft.
57 //
58 // This is used to assist a corner case described in |IsKeyDownAltRight|.
59 bool IsKeyDownCtrlLeft(int action, int virtual_key) {
60  return virtual_key == VK_LCONTROL &&
61  (action == WM_KEYDOWN || action == WM_SYSKEYDOWN);
62 }
63 
64 // Returns if a character sent by Win32 is a dead key.
65 bool IsDeadKey(uint32_t ch) {
66  return (ch & kDeadKeyCharMask) != 0;
67 }
68 
69 char32_t CodePointFromSurrogatePair(wchar_t high, wchar_t low) {
70  return 0x10000 + ((static_cast<char32_t>(high) & 0x000003FF) << 10) +
71  (low & 0x3FF);
72 }
73 
74 uint16_t ResolveKeyCode(uint16_t original, bool extended, uint8_t scancode) {
75  switch (original) {
76  case VK_SHIFT:
77  case VK_LSHIFT:
78  return MapVirtualKey(scancode, MAPVK_VSC_TO_VK_EX);
79  case VK_MENU:
80  case VK_LMENU:
81  return extended ? VK_RMENU : VK_LMENU;
82  case VK_CONTROL:
83  case VK_LCONTROL:
84  return extended ? VK_RCONTROL : VK_LCONTROL;
85  default:
86  return original;
87  }
88 }
89 
90 bool IsPrintable(uint32_t c) {
91  constexpr char32_t kMinPrintable = ' ';
92  constexpr char32_t kDelete = 0x7F;
93  return c >= kMinPrintable && c != kDelete;
94 }
95 
96 bool IsSysAction(UINT action) {
97  return action == WM_SYSKEYDOWN || action == WM_SYSKEYUP ||
98  action == WM_SYSCHAR || action == WM_SYSDEADCHAR;
99 }
100 
101 } // namespace
102 
104  : window_delegate_(delegate),
105  last_key_is_ctrl_left_down(false),
106  should_synthesize_ctrl_left_up(false),
107  processing_event_(false) {}
108 
109 void KeyboardManager::RedispatchEvent(std::unique_ptr<PendingEvent> event) {
110  for (const Win32Message& message : event->session) {
111  // Never redispatch sys keys, because their original messages have been
112  // passed to the system default processor.
113  if (IsSysAction(message.action)) {
114  continue;
115  }
116  pending_redispatches_.push_back(message);
117  UINT result = window_delegate_->Win32DispatchMessage(
119  if (result != 0) {
120  FML_LOG(ERROR) << "Unable to synthesize event for keyboard event.";
121  }
122  }
123  if (pending_redispatches_.size() > kMaxPendingEvents) {
124  FML_LOG(ERROR)
125  << "There are " << pending_redispatches_.size()
126  << " keyboard events that have not yet received a response from the "
127  << "framework. Are responses being sent?";
128  }
129 }
130 
131 bool KeyboardManager::RemoveRedispatchedMessage(UINT const action,
132  WPARAM const wparam,
133  LPARAM const lparam) {
134  for (auto iter = pending_redispatches_.begin();
135  iter != pending_redispatches_.end(); ++iter) {
136  if (action == iter->action && wparam == iter->wparam) {
137  pending_redispatches_.erase(iter);
138  return true;
139  }
140  }
141  return false;
142 }
143 
145  WPARAM const wparam,
146  LPARAM const lparam) {
147  if (RemoveRedispatchedMessage(action, wparam, lparam)) {
148  return false;
149  }
150  switch (action) {
151  case WM_DEADCHAR:
152  case WM_SYSDEADCHAR:
153  case WM_CHAR:
154  case WM_SYSCHAR: {
155  const Win32Message message =
156  Win32Message{.action = action, .wparam = wparam, .lparam = lparam};
157  current_session_.push_back(message);
158 
159  char32_t code_point;
160  if (message.IsHighSurrogate()) {
161  // A high surrogate is always followed by a low surrogate. Process the
162  // session later and consider this message as handled.
163  return true;
164  } else if (message.IsLowSurrogate()) {
165  const Win32Message* last_message =
166  current_session_.size() <= 1
167  ? nullptr
168  : &current_session_[current_session_.size() - 2];
169  if (last_message == nullptr || !last_message->IsHighSurrogate()) {
170  return false;
171  }
172  // A low surrogate always follows a high surrogate, marking the end of
173  // a char session. Process the session after the if clause.
174  code_point =
175  CodePointFromSurrogatePair(last_message->wparam, message.wparam);
176  } else {
177  // A non-surrogate character always appears alone. Process the session
178  // after the if clause.
179  code_point = static_cast<wchar_t>(message.wparam);
180  }
181 
182  // If this char message is preceded by a key down message, then dispatch
183  // the key down message as a key down event first, and only dispatch the
184  // OnText if the key down event is not handled.
185  if (current_session_.front().IsGeneralKeyDown()) {
186  const Win32Message first_message = current_session_.front();
187  const uint8_t scancode = (lparam >> 16) & 0xff;
188  const uint16_t key_code = first_message.wparam;
189  const bool extended = ((lparam >> 24) & 0x01) == 0x01;
190  const bool was_down = lparam & 0x40000000;
191  // Certain key combinations yield control characters as WM_CHAR's
192  // lParam. For example, 0x01 for Ctrl-A. Filter these characters. See
193  // https://docs.microsoft.com/en-us/windows/win32/learnwin32/accelerator-tables
194  char32_t character;
195  if (action == WM_DEADCHAR || action == WM_SYSDEADCHAR) {
196  // Mask the resulting char with kDeadKeyCharMask anyway, because in
197  // rare cases the bit is *not* set (US INTL Shift-6 circumflex, see
198  // https://github.com/flutter/flutter/issues/92654 .)
199  character =
200  window_delegate_->Win32MapVkToChar(key_code) | kDeadKeyCharMask;
201  } else {
202  character = IsPrintable(code_point) ? code_point : 0;
203  }
204  auto event = std::make_unique<PendingEvent>(PendingEvent{
205  .key = key_code,
206  .scancode = scancode,
207  .action = static_cast<UINT>(action == WM_SYSCHAR ? WM_SYSKEYDOWN
208  : WM_KEYDOWN),
209  .character = character,
210  .extended = extended,
211  .was_down = was_down,
212  .session = std::move(current_session_),
213  });
214 
215  pending_events_.push_back(std::move(event));
216  ProcessNextEvent();
217 
218  // SYS messages must not be consumed by `HandleMessage` so that they are
219  // forwarded to the system.
220  return !IsSysAction(action);
221  }
222 
223  // If the charcter session is not preceded by a key down message,
224  // mark PendingEvent::action as WM_CHAR, informing |PerformProcessEvent|
225  // to dispatch the text content immediately.
226  //
227  // Only WM_CHAR should be treated as characters. WM_SYS*CHAR are not part
228  // of text input, and WM_DEADCHAR will be incorporated into a later
229  // WM_CHAR with the full character.
230  if (action == WM_CHAR) {
231  auto event = std::make_unique<PendingEvent>(PendingEvent{
232  .action = WM_CHAR,
233  .character = code_point,
234  .session = std::move(current_session_),
235  });
236  pending_events_.push_back(std::move(event));
237  ProcessNextEvent();
238  }
239  return true;
240  }
241 
242  case WM_KEYDOWN:
243  case WM_SYSKEYDOWN:
244  case WM_KEYUP:
245  case WM_SYSKEYUP: {
246  if (wparam == VK_PACKET) {
247  return false;
248  }
249 
250  const uint8_t scancode = (lparam >> 16) & 0xff;
251  const bool extended = ((lparam >> 24) & 0x01) == 0x01;
252  // If the key is a modifier, get its side.
253  const uint16_t key_code = ResolveKeyCode(wparam, extended, scancode);
254  const bool was_down = lparam & 0x40000000;
255 
256  // Detect a pattern of key events in order to forge a CtrlLeft up event.
257  // See |IsKeyDownAltRight| for explanation.
258  if (IsKeyDownAltRight(action, key_code, extended)) {
259  if (last_key_is_ctrl_left_down) {
260  should_synthesize_ctrl_left_up = true;
261  }
262  }
263  if (IsKeyDownCtrlLeft(action, key_code)) {
264  last_key_is_ctrl_left_down = true;
265  ctrl_left_scancode = scancode;
266  should_synthesize_ctrl_left_up = false;
267  } else {
268  last_key_is_ctrl_left_down = false;
269  }
270  if (IsKeyUpAltRight(action, key_code, extended)) {
271  if (should_synthesize_ctrl_left_up) {
272  should_synthesize_ctrl_left_up = false;
273  const LPARAM lParam =
274  (1 /* repeat_count */ << 0) | (ctrl_left_scancode << 16) |
275  (0 /* extended */ << 24) | (1 /* prev_state */ << 30) |
276  (1 /* transition */ << 31);
277  window_delegate_->Win32DispatchMessage(WM_KEYUP, VK_CONTROL, lParam);
278  }
279  }
280 
281  current_session_.clear();
282  current_session_.push_back(
283  Win32Message{.action = action, .wparam = wparam, .lparam = lparam});
284  const bool is_keydown_message =
285  (action == WM_KEYDOWN || action == WM_SYSKEYDOWN);
286  // Check if this key produces a character by peeking if this key down
287  // message has a following char message. Certain key messages are not
288  // followed by char messages even though `MapVirtualKey` returns a valid
289  // character (such as Ctrl + Digit, see
290  // https://github.com/flutter/flutter/issues/85587 ).
291  unsigned int character = window_delegate_->Win32MapVkToChar(wparam);
292  UINT next_key_action = PeekNextMessageType(WM_KEYFIRST, WM_KEYLAST);
293  bool has_char_action =
294  (next_key_action == WM_DEADCHAR ||
295  next_key_action == WM_SYSDEADCHAR || next_key_action == WM_CHAR ||
296  next_key_action == WM_SYSCHAR);
297  if (character > 0 && is_keydown_message && has_char_action) {
298  // This key down message has a following char message. Process this
299  // session in the char message, because the character for the key call
300  // should be decided by the char events. Consider this message as
301  // handled.
302  return true;
303  }
304 
305  // This key down message is not followed by a char message. Conclude this
306  // session.
307  auto event = std::make_unique<PendingEvent>(PendingEvent{
308  .key = key_code,
309  .scancode = scancode,
310  .action = action,
311  .character = 0,
312  .extended = extended,
313  .was_down = was_down,
314  .session = std::move(current_session_),
315  });
316  pending_events_.push_back(std::move(event));
317  ProcessNextEvent();
318  // SYS messages must not be consumed by `HandleMessage` so that they are
319  // forwarded to the system.
320  return !IsSysAction(action);
321  }
322  default:
323  FML_LOG(FATAL) << "No event handler for keyboard event with action "
324  << action;
325  }
326  return false;
327 }
328 
329 void KeyboardManager::ProcessNextEvent() {
330  if (processing_event_ || pending_events_.empty()) {
331  return;
332  }
333  processing_event_ = true;
334  auto pending_event = std::move(pending_events_.front());
335  pending_events_.pop_front();
336  PerformProcessEvent(std::move(pending_event), [this] {
337  FML_DCHECK(processing_event_);
338  processing_event_ = false;
339  ProcessNextEvent();
340  });
341 }
342 
343 void KeyboardManager::PerformProcessEvent(std::unique_ptr<PendingEvent> event,
344  std::function<void()> callback) {
345  // PendingEvent::action being WM_CHAR means this is a char message without
346  // a preceding key message, and should be dispatched immediately.
347  if (event->action == WM_CHAR) {
348  DispatchText(*event);
349  callback();
350  return;
351  }
352 
353  // A unique_ptr can't be sent into a lambda without C++23's
354  // move_only_function. Until then, `event` is sent as a raw pointer, hoping
355  // WindowDelegate::OnKey to correctly call it once and only once.
356  PendingEvent* event_p = event.release();
357  window_delegate_->OnKey(
358  event_p->key, event_p->scancode, event_p->action, event_p->character,
359  event_p->extended, event_p->was_down,
360  [this, event_p, callback = std::move(callback)](bool handled) {
361  HandleOnKeyResult(std::unique_ptr<PendingEvent>(event_p), handled);
362  callback();
363  });
364 }
365 
366 void KeyboardManager::HandleOnKeyResult(std::unique_ptr<PendingEvent> event,
367  bool framework_handled) {
368  const UINT last_action = event->session.back().action;
369  // SYS messages must not be redispached, and their text content is not
370  // dispatched either.
371  bool handled = framework_handled || IsSysAction(last_action);
372 
373  if (handled) {
374  return;
375  }
376 
377  // Only WM_CHAR should be treated as characters. WM_SYS*CHAR are not part of
378  // text input, and WM_DEADCHAR will be incorporated into a later WM_CHAR with
379  // the full character.
380  if (last_action == WM_CHAR) {
381  DispatchText(*event);
382  }
383 
384  RedispatchEvent(std::move(event));
385 }
386 
387 void KeyboardManager::DispatchText(const PendingEvent& event) {
388  // Check if the character is printable based on the last wparam, which works
389  // even if the last wparam is a low surrogate, because the only unprintable
390  // keys defined by `IsPrintable` are certain characters at lower ASCII range.
391  // These ASCII control characters are sent as WM_CHAR events for all control
392  // key shortcuts.
393  FML_DCHECK(!event.session.empty());
394  bool is_printable = IsPrintable(event.session.back().wparam);
395  bool valid = event.character != 0 && is_printable;
396  if (valid) {
397  auto text = EncodeUtf16(event.character);
398  window_delegate_->OnText(text);
399  }
400 }
401 
402 UINT KeyboardManager::PeekNextMessageType(UINT wMsgFilterMin,
403  UINT wMsgFilterMax) {
404  MSG next_message;
405  BOOL has_msg = window_delegate_->Win32PeekMessage(
406  &next_message, wMsgFilterMin, wMsgFilterMax, PM_NOREMOVE);
407  if (!has_msg) {
408  return 0;
409  }
410  return next_message.message;
411 }
412 
413 } // namespace flutter
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