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// 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 <assert.h>
#include <memory>
#include <string>
#include "flutter/fml/logging.h"
#include "flutter/shell/platform/windows/keyboard_manager.h"
#include "flutter/shell/platform/windows/keyboard_utils.h"
namespace flutter {
namespace {
// The maximum number of pending events to keep before
// emitting a warning on the console about unhandled events.
static constexpr int kMaxPendingEvents = 1000;
// Returns true if this key is an AltRight key down event.
//
// This is used to resolve an issue where an AltGr press causes CtrlLeft to hang
// when pressed, as reported in https://github.com/flutter/flutter/issues/78005.
//
// When AltGr is pressed (in a supporting layout such as Spanish), Win32 first
// fires a fake CtrlLeft down event, then an AltRight down event.
// This is significant because this fake CtrlLeft down event will not be paired
// with a up event, which is fine until Flutter redispatches the CtrlDown
// event, which Win32 then interprets as a real event, leaving both Win32 and
// the Flutter framework thinking that CtrlLeft is still pressed.
//
// To resolve this, Flutter recognizes this fake CtrlLeft down event using the
// following AltRight down event. Flutter then forges a CtrlLeft key up event
// immediately after the corresponding AltRight key up event.
//
// One catch is that it is impossible to distinguish the fake CtrlLeft down
// from a normal CtrlLeft down (followed by a AltRight down), since they
// contain the exactly same information, including the GetKeyState result.
// Fortunately, this will require the two events to occur *really* close, which
// would be rare, and a misrecognition would only cause a minor consequence
// where the CtrlLeft is released early; the later, real, CtrlLeft up event will
// be ignored.
static bool IsKeyDownAltRight(int action, int virtual_key, bool extended) {
return virtual_key == VK_RMENU && extended &&
(action == WM_KEYDOWN || action == WM_SYSKEYDOWN);
}
// Returns true if this key is a key up event of AltRight.
//
// This is used to assist a corner case described in |IsKeyDownAltRight|.
static bool IsKeyUpAltRight(int action, int virtual_key, bool extended) {
return virtual_key == VK_RMENU && extended &&
(action == WM_KEYUP || action == WM_SYSKEYUP);
}
// Returns true if this key is a key down event of CtrlLeft.
//
// This is used to assist a corner case described in |IsKeyDownAltRight|.
static bool IsKeyDownCtrlLeft(int action, int virtual_key) {
return virtual_key == VK_LCONTROL &&
(action == WM_KEYDOWN || action == WM_SYSKEYDOWN);
}
// Returns if a character sent by Win32 is a dead key.
static bool IsDeadKey(uint32_t ch) {
return (ch & kDeadKeyCharMask) != 0;
}
static char32_t CodePointFromSurrogatePair(wchar_t high, wchar_t low) {
return 0x10000 + ((static_cast<char32_t>(high) & 0x000003FF) << 10) +
(low & 0x3FF);
}
static uint16_t ResolveKeyCode(uint16_t original,
bool extended,
uint8_t scancode) {
switch (original) {
case VK_SHIFT:
case VK_LSHIFT:
return MapVirtualKey(scancode, MAPVK_VSC_TO_VK_EX);
case VK_MENU:
case VK_LMENU:
return extended ? VK_RMENU : VK_LMENU;
case VK_CONTROL:
case VK_LCONTROL:
return extended ? VK_RCONTROL : VK_LCONTROL;
default:
return original;
}
}
static bool IsPrintable(uint32_t c) {
constexpr char32_t kMinPrintable = ' ';
constexpr char32_t kDelete = 0x7F;
return c >= kMinPrintable && c != kDelete;
}
static bool IsSysAction(UINT action) {
return action == WM_SYSKEYDOWN || action == WM_SYSKEYUP ||
action == WM_SYSCHAR || action == WM_SYSDEADCHAR;
}
} // namespace
KeyboardManager::KeyboardManager(WindowDelegate* delegate)
: window_delegate_(delegate),
last_key_is_ctrl_left_down(false),
should_synthesize_ctrl_left_up(false),
processing_event_(false) {}
void KeyboardManager::RedispatchEvent(std::unique_ptr<PendingEvent> event) {
for (const Win32Message& message : event->session) {
// Never redispatch sys keys, because their original messages have been
// passed to the system default processor.
if (IsSysAction(message.action)) {
continue;
}
pending_redispatches_.push_back(message);
UINT result = window_delegate_->Win32DispatchMessage(
message.action, message.wparam, message.lparam);
if (result != 0) {
FML_LOG(ERROR) << "Unable to synthesize event for keyboard event.";
}
}
if (pending_redispatches_.size() > kMaxPendingEvents) {
FML_LOG(ERROR)
<< "There are " << pending_redispatches_.size()
<< " keyboard events that have not yet received a response from the "
<< "framework. Are responses being sent?";
}
}
bool KeyboardManager::RemoveRedispatchedMessage(UINT const action,
WPARAM const wparam,
LPARAM const lparam) {
for (auto iter = pending_redispatches_.begin();
iter != pending_redispatches_.end(); ++iter) {
if (action == iter->action && wparam == iter->wparam) {
pending_redispatches_.erase(iter);
return true;
}
}
return false;
}
bool KeyboardManager::HandleMessage(UINT const action,
WPARAM const wparam,
LPARAM const lparam) {
if (RemoveRedispatchedMessage(action, wparam, lparam)) {
return false;
}
switch (action) {
case WM_DEADCHAR:
case WM_SYSDEADCHAR:
case WM_CHAR:
case WM_SYSCHAR: {
const Win32Message message =
Win32Message{.action = action, .wparam = wparam, .lparam = lparam};
current_session_.push_back(message);
char32_t code_point;
if (message.IsHighSurrogate()) {
// A high surrogate is always followed by a low surrogate. Process the
// session later and consider this message as handled.
return true;
} else if (message.IsLowSurrogate()) {
const Win32Message* last_message =
current_session_.size() <= 1
? nullptr
: &current_session_[current_session_.size() - 2];
if (last_message == nullptr || !last_message->IsHighSurrogate()) {
return false;
}
// A low surrogate always follows a high surrogate, marking the end of
// a char session. Process the session after the if clause.
code_point =
CodePointFromSurrogatePair(last_message->wparam, message.wparam);
} else {
// A non-surrogate character always appears alone. Process the session
// after the if clause.
code_point = static_cast<wchar_t>(message.wparam);
}
// If this char message is preceded by a key down message, then dispatch
// the key down message as a key down event first, and only dispatch the
// OnText if the key down event is not handled.
if (current_session_.front().IsGeneralKeyDown()) {
const Win32Message first_message = current_session_.front();
const uint8_t scancode = (lparam >> 16) & 0xff;
const uint16_t key_code = first_message.wparam;
const bool extended = ((lparam >> 24) & 0x01) == 0x01;
const bool was_down = lparam & 0x40000000;
// Certain key combinations yield control characters as WM_CHAR's
// lParam. For example, 0x01 for Ctrl-A. Filter these characters. See
// https://docs.microsoft.com/en-us/windows/win32/learnwin32/accelerator-tables
char32_t character;
if (action == WM_DEADCHAR || action == WM_SYSDEADCHAR) {
// Mask the resulting char with kDeadKeyCharMask anyway, because in
// rare cases the bit is *not* set (US INTL Shift-6 circumflex, see
// https://github.com/flutter/flutter/issues/92654 .)
character =
window_delegate_->Win32MapVkToChar(key_code) | kDeadKeyCharMask;
} else {
character = IsPrintable(code_point) ? code_point : 0;
}
auto event = std::make_unique<PendingEvent>(PendingEvent{
.key = key_code,
.scancode = scancode,
.action = static_cast<UINT>(action == WM_SYSCHAR ? WM_SYSKEYDOWN
: WM_KEYDOWN),
.character = character,
.extended = extended,
.was_down = was_down,
.session = std::move(current_session_),
});
pending_events_.push_back(std::move(event));
ProcessNextEvent();
// SYS messages must not be consumed by `HandleMessage` so that they are
// forwarded to the system.
return !IsSysAction(action);
}
// If the charcter session is not preceded by a key down message,
// mark PendingEvent::action as WM_CHAR, informing |PerformProcessEvent|
// to dispatch the text content immediately.
//
// Only WM_CHAR should be treated as characters. WM_SYS*CHAR are not part
// of text input, and WM_DEADCHAR will be incorporated into a later
// WM_CHAR with the full character.
if (action == WM_CHAR) {
auto event = std::make_unique<PendingEvent>(PendingEvent{
.action = WM_CHAR,
.character = code_point,
.session = std::move(current_session_),
});
pending_events_.push_back(std::move(event));
ProcessNextEvent();
}
return true;
}
case WM_KEYDOWN:
case WM_SYSKEYDOWN:
case WM_KEYUP:
case WM_SYSKEYUP: {
if (wparam == VK_PACKET) {
return false;
}
const uint8_t scancode = (lparam >> 16) & 0xff;
const bool extended = ((lparam >> 24) & 0x01) == 0x01;
// If the key is a modifier, get its side.
const uint16_t key_code = ResolveKeyCode(wparam, extended, scancode);
const bool was_down = lparam & 0x40000000;
// Detect a pattern of key events in order to forge a CtrlLeft up event.
// See |IsKeyDownAltRight| for explanation.
if (IsKeyDownAltRight(action, key_code, extended)) {
if (last_key_is_ctrl_left_down) {
should_synthesize_ctrl_left_up = true;
}
}
if (IsKeyDownCtrlLeft(action, key_code)) {
last_key_is_ctrl_left_down = true;
ctrl_left_scancode = scancode;
should_synthesize_ctrl_left_up = false;
} else {
last_key_is_ctrl_left_down = false;
}
if (IsKeyUpAltRight(action, key_code, extended)) {
if (should_synthesize_ctrl_left_up) {
should_synthesize_ctrl_left_up = false;
const LPARAM lParam =
(1 /* repeat_count */ << 0) | (ctrl_left_scancode << 16) |
(0 /* extended */ << 24) | (1 /* prev_state */ << 30) |
(1 /* transition */ << 31);
window_delegate_->Win32DispatchMessage(WM_KEYUP, VK_CONTROL, lParam);
}
}
current_session_.clear();
current_session_.push_back(
Win32Message{.action = action, .wparam = wparam, .lparam = lparam});
const bool is_keydown_message =
(action == WM_KEYDOWN || action == WM_SYSKEYDOWN);
// Check if this key produces a character by peeking if this key down
// message has a following char message. Certain key messages are not
// followed by char messages even though `MapVirtualKey` returns a valid
// character (such as Ctrl + Digit, see
// https://github.com/flutter/flutter/issues/85587 ).
unsigned int character = window_delegate_->Win32MapVkToChar(wparam);
UINT next_key_action = PeekNextMessageType(WM_KEYFIRST, WM_KEYLAST);
bool has_char_action =
(next_key_action == WM_DEADCHAR ||
next_key_action == WM_SYSDEADCHAR || next_key_action == WM_CHAR ||
next_key_action == WM_SYSCHAR);
if (character > 0 && is_keydown_message && has_char_action) {
// This key down message has a following char message. Process this
// session in the char message, because the character for the key call
// should be decided by the char events. Consider this message as
// handled.
return true;
}
// This key down message is not followed by a char message. Conclude this
// session.
auto event = std::make_unique<PendingEvent>(PendingEvent{
.key = key_code,
.scancode = scancode,
.action = action,
.character = 0,
.extended = extended,
.was_down = was_down,
.session = std::move(current_session_),
});
pending_events_.push_back(std::move(event));
ProcessNextEvent();
// SYS messages must not be consumed by `HandleMessage` so that they are
// forwarded to the system.
return !IsSysAction(action);
}
default:
assert(false);
}
return false;
}
void KeyboardManager::ProcessNextEvent() {
if (processing_event_ || pending_events_.empty()) {
return;
}
processing_event_ = true;
auto pending_event = std::move(pending_events_.front());
pending_events_.pop_front();
PerformProcessEvent(std::move(pending_event), [this] {
assert(processing_event_);
processing_event_ = false;
ProcessNextEvent();
});
}
void KeyboardManager::PerformProcessEvent(std::unique_ptr<PendingEvent> event,
std::function<void()> callback) {
// PendingEvent::action being WM_CHAR means this is a char message without
// a preceding key message, and should be dispatched immediately.
if (event->action == WM_CHAR) {
DispatchText(*event);
callback();
return;
}
// A unique_ptr can't be sent into a lambda without C++23's
// move_only_function. Until then, `event` is sent as a raw pointer, hoping
// WindowDelegate::OnKey to correctly call it once and only once.
PendingEvent* event_p = event.release();
window_delegate_->OnKey(
event_p->key, event_p->scancode, event_p->action, event_p->character,
event_p->extended, event_p->was_down,
[this, event_p, callback = std::move(callback)](bool handled) {
HandleOnKeyResult(std::unique_ptr<PendingEvent>(event_p), handled);
callback();
});
}
void KeyboardManager::HandleOnKeyResult(std::unique_ptr<PendingEvent> event,
bool framework_handled) {
const UINT last_action = event->session.back().action;
// SYS messages must not be redispached, and their text content is not
// dispatched either.
bool handled = framework_handled || IsSysAction(last_action);
if (handled) {
return;
}
// Only WM_CHAR should be treated as characters. WM_SYS*CHAR are not part of
// text input, and WM_DEADCHAR will be incorporated into a later WM_CHAR with
// the full character.
if (last_action == WM_CHAR) {
DispatchText(*event);
}
RedispatchEvent(std::move(event));
}
void KeyboardManager::DispatchText(const PendingEvent& event) {
// Check if the character is printable based on the last wparam, which works
// even if the last wparam is a low surrogate, because the only unprintable
// keys defined by `IsPrintable` are certain characters at lower ASCII range.
// These ASCII control characters are sent as WM_CHAR events for all control
// key shortcuts.
assert(!event.session.empty());
bool is_printable = IsPrintable(event.session.back().wparam);
bool valid = event.character != 0 && is_printable;
if (valid) {
auto text = EncodeUtf16(event.character);
window_delegate_->OnText(text);
}
}
UINT KeyboardManager::PeekNextMessageType(UINT wMsgFilterMin,
UINT wMsgFilterMax) {
MSG next_message;
BOOL has_msg = window_delegate_->Win32PeekMessage(
&next_message, wMsgFilterMin, wMsgFilterMax, PM_NOREMOVE);
if (!has_msg) {
return 0;
}
return next_message.message;
}
} // namespace flutter