I am running into an odd issue which I don't really know how to troubleshoot. I am writing code in C++ which is supposed to trigger events when keys are pressed. I can detect keypress and release fine, using GetAsyncKeystate, but I cannot reliably convert the detected keystates into unicode. (note that I am using Qt, but that shouldn't really matter)
My press / release detection:
// This function is called in a loop
void KeyboardApi::Check()
{
bool stat = false;
for (int i = 7; i < 255; i++) { // 0 undefined, 3 VK_CANCEL can be ignored, 1 2 4 5 6 mouse keys, these are ignored
stat = ((GetAsyncKeyState(i) & 0x8000) != 0);
if (this->first_time) { // To prevent reporting keypresses upon initialization
this->first_time = false;
this->keystate[i] = stat;
continue;
}
if (stat != this->keystate[i]) {
this->keystate[i] = stat;
if (i == VK_SHIFT)
this->shift = stat;
else if (i == VK_CONTROL)
this->ctrl = stat;
else if (i == VK_MENU)
this->alt = stat;
HKL locale = GetKeyboardLayout(GetCurrentThreadId());
// ---!! If this portion is commented, the code does not work correctly.
// if this portion is *not* commented, the code works fine...
/*
std::wcout << "args for keycode_to_unicode:" << std::endl
<< " keycode: " << i << std::endl
<< " locale: " << locale << std::endl
<< " shift: " << this->shift << std::endl;
*/
// ---!!
QString key_string = keycode_to_unicode(i, locale, this->shift);
if (stat)
std::wcout << "Key pressed: " << i << " unicode: " << key_string.toStdWString() << std::endl;
}
}
}
And the keycode_to_unicode function:
QString keycode_to_unicode(unsigned int key, HKL keyboardLayoutHandle, bool shiftPressed)
{
int scanCodeEx = MapVirtualKeyExW(key, MAPVK_VK_TO_VSC_EX, keyboardLayoutHandle);
if (scanCodeEx > 0) {
unsigned char lpKeyState[256];
if (shiftPressed) {
lpKeyState[VK_SHIFT] = 0x80;
lpKeyState[VK_LSHIFT] = 0x80;
}
wchar_t buffer[5];
int rc = ToUnicodeEx(key, scanCodeEx, lpKeyState, buffer, 5, 0, keyboardLayoutHandle);
if (rc > 0) {
return QString::fromWCharArray(buffer);
} else {
// It's a dead key; let's flush out whats stored in the keyboard state.
rc = ToUnicodeEx(key, scanCodeEx, lpKeyState, buffer, 5, 0, keyboardLayoutHandle);
return QString();
}
}
return QString();
}
So the odd thing is that KeyboardApi::Check() works fine when I have the debug output there, but when I don't have it the conversion to unicode goes wrong. For example, when I press the 'A' key the first time, 'a' is outputted. The second time, 'β', 'β', etc.
EDIT:
You may ask yourself why I am not using Qt's build-in onKeyPress... This is because my code is injected into other processes, thus I cannot use this approach.
It turned out to be an issue with keycode_to_unicode!
In my code, I had:
unsigned char lpKeyState[256];
Which means the array is not initialized; its contents could be anything. Replacing it with:
unsigned char lpKeyState[256] = {0};
Fixed the issue of odd input. It turned out I also had some other issues (specifically with dead-keys). I altered my code a bit and am now able to properly detect dead-keys when they are pressed, though I have not succeeded yet in combining the dead-keys with follow-up characters to detect characters with accents. For the sake of completeness, here follows the modified code:
Note: it does not take into account capslock.
QString KeyboardApi::keycode_to_unicode(unsigned int key, HKL keyboardLayoutHandle, bool shiftPressed, bool ctrlPressed, bool altPressed, bool capslock)
{
int scanCodeEx = MapVirtualKeyExW(key, MAPVK_VK_TO_VSC_EX, keyboardLayoutHandle);
if (scanCodeEx <= 0)
return QString();
unsigned char lpKeyState[256] = {0};
if (shiftPressed) {
lpKeyState[VK_SHIFT] = 0x80;
lpKeyState[VK_LSHIFT] = 0x80;
}
if (ctrlPressed)
lpKeyState[VK_CONTROL] = 0x80;
if (altPressed)
lpKeyState[VK_MENU] = 0x80;
if (capslock)
lpKeyState[VK_CAPITAL] = 0x01;
wchar_t buffer[5];
ToUnicodeEx(key, scanCodeEx, lpKeyState, buffer, 5, 0, keyboardLayoutHandle);
QString ret = QString::fromWCharArray(buffer);
ret.truncate(1);
return ret;
}
Qt::Key KeyboardApi::unicode_to_qtkey(QString key)
{
unsigned int code = key[0].unicode();
if (key[0].unicode() >= 'a' && key[0].unicode() <= 'z') {
code = key[0].unicode() - 'a' + Qt::Key_A;
}
return (Qt::Key)code;
}
void KeyboardApi::Check()
{
bool init = this->first_time;
if (this->first_time)
this->first_time = false;
bool stat = false;
for (int i = 7; i < 255; i++) { // yes, 255 is NOT valid! // 0 undefined, 3 VK_CANCEL can be ignored, 1 2 4 5 6 mouse keys
stat = ((GetAsyncKeyState(i) & 0x8000) != 0);
if (stat == this->keystate[i])
continue;
this->keystate[i] = stat;
if (i == VK_SHIFT)
this->shift = stat;
else if (i == VK_CONTROL)
this->ctrl = stat;
else if (i == VK_MENU)
this->alt = stat;
else if (i == VK_CAPITAL)
this->capslock = stat;
HKL locale = GetKeyboardLayout(GetCurrentThreadId());
QString key_string = keycode_to_unicode(i, locale, this->shift, this->ctrl, this->alt, false);
// See qkeymapper_win.cpp for the table used to convert windows virtual key codes to Qt::Key
Qt::Key key = key_string.isEmpty() ? (Qt::Key)win_vk_to_qt_key[i] : unicode_to_qtkey(key_string);
if (init || i == VK_SHIFT || i == VK_CONTROL || i == VK_MENU)
continue;
if (stat) {
emit this->OnKeyDown(this, QKeyEvent(QEvent::KeyPress, key, mods, key_string));
} else
emit this->OnKeyUp(this, QKeyEvent(QEvent::KeyPress, key, mods, key_string));
}
}