In Qt's QKeyEvent I can check whether Ctrl was pressed by checking if ev->key() is Qt::Key_Control. But how can I distinguish between the left and right Ctrl keys?
I also need the same thing for Alt and Shift keys.
There is no way to do this using pure Qt methods, as far as I know.
Depending on your platform, however, you might be able to distinguish between the keys using the QKeyEvent::nativeScanCode() method instead of QKeyEvent::key().
For example, on Windows you should be able to test which Ctrl key was pressed as follows:
if (event->nativeScanCode() == VK_LCONTROL) {
// left control pressed
} else if (event->nativeScanCode() == VK_RCONTROL) {
// right control pressed
}
According to the Qt Namespace Reference, the enum Qt::Key has a different value for Qt::Key_Alt and Qt::Key_AltGr.
However, enum Qt::KeyboardModifier and enum Qt::Modifier don't see the pair of keys as different modifiers.
(note: I would have posted this as a comment but I don't have enough rep. yet)
Left and Right keys are part of virtual key code -> use nativeVirtualKey() to compare with windows VK_* enums instead of nativescancode().
If VK_RCONTROLdoes not work, check your nativeScanCode value of ctrl-right:
std::cout<<keyEvent->nativeScanCode(); and use this value:
int control_right = 285;
if(key->nativeScanCode() == control_right){...
Related
I would like to be able to check if the key is pressed at any time. I imagine such a solution:
void MyQQuickPaintedItem::keyPressEvent(QKeyEvent * event)
{
isKeyPressed[ event->key() ] = 1;
}
void MyQQuickPaintedItem::keyReleaseEvent(QKeyEvent *event)
{
isKeyPressed[ event->key() ] = 0;
}
To check if the right arrow key is pressed it would be enough to check isKeyPressed[ Qt::Key_Right ] value.
I implemented it and... it doesn't work. I don't mean that program crashes. isKeyPressed[ Qt::Key_Right ] is just always 0, even if I'm pressing this right arrow key or any other key.
EDIT:
One of header files:
...
bool isKeyPressed[255];
...
One of linked files:
...
extern bool isKeyPressed[255];
...
I don't know exactly how big isKeyPressed should be, but I don't get SIGSEGV, so the size is probably ok.
you normally dont address the problem like that... at least not using QT...
if you are interested to "catch" some key pressed events, then Qt offers ways to do that
what you can do is "connect" the shortcut to a lambda or a slot and inside there do what ever you need... like e.g. catching when the user press "control + i"
connect(new QShortcut(QKeySequence(Qt::CTRL + Qt::Key_I), this), &QShortcut::activated, [](){qDebug() << "Here we are!";});
Instead of an array you can use the map, if you are not interested in the order then you can use unordered_maps which is faster. There are rather few keys so I think the program will run fast anyway.
To handle text input I've set up a char-event callback with glfwSetCharCallback, and to handle non-text keypresses (arrow keys & hotkeys) I've set up a key-event callback with glfwSetKeyCallback.
What happens in this situation is that for a key press of a character key, I get two calls, one in the key-event callback, and then one in the char-event callback. This can cause unwanted effects - for example let's suppose the user configured the key "a" to enter "Append Mode" of a text editor - after it enters the mode it will also enter the character "a".. Is there a good way to handle this?
So far I've relied on both events arriving together before glfwPollEvents returns, and have merged them. But I get reports that this scheme doesn't work well on some Ubuntu systems..
I've been having trouble with this one as well. After some rudimentary debugging I found that if you press, hold then release a 'typable' key (meaning a key which may fire both the glfwKeyCallback and glfwCharCallback), the output is as follows:
KeyCallback - pressed
CharCallback - typed
KeyCallback - repeated
CharCallback - typed
(3. and 4. repeat until key is released)
KeyCallback - released
With this, and judging from the fact that there is a 0ms delay between the two events firing, they're probably fired sequentially. The solution I came up with (is rather janky), and involves creating some sort of KeyEvent structure:
(examples are in C++)
enum KeyEventType
{
Pressed,
Repeated,
Released
}
struct KeyEvent
{
KeyEventType Type;
int Key;
unsigned char Codepoint;
bool IsTyped;
}
and store it along with an index variable, such as
[main/input class]
std::vector<KeyEvent> m_KeyEvents;
size_t m_LastKeyEventIndex;
in the main file.
Then, when the glfwKeyCallback fires, push a new KeyEvent into the vector:
[glfwKeyCallback]
KeyEventType type = (action == GLFW_PRESS ? KeyEventType::Pressed : (action == GLFW_REPEAT ? KeyEventType::Repeated : KeyEventType::Released));
KeyEvent event = KeyEvent(type, key);
m_KeyEvents.push_back(event);
m_LastKeyEventIndex = m_KeyEvents.size() - 1;
and if the glfwCharCallback fires, we know from the debugging that it should be (immediately) after the corresponding keyCallback event, so you can modify the last added entry in the vector to add the codepoint and mark it as a 'typed' event, after-the-fact. This also gives the added benefit of tying the actual key that was pressed to the generated codepoint, which could come in useful.
[glfwCharCallback]
m_KeyEvents.at(m_LastKeyEventIndex).Codepoint = codepoint;
m_KeyEvents.at(m_LastKeyEventIndex).IsTyped = true;
Finally, in the main loop when you go to call glfwPollEvents(), process all those pending KeyEvents and then clear the vector and reset the index.
I haven't fully tested this yet, but some very rudimentary debugging shows this as a promising solution, resulting in the following*:
*I'm using a custom Key enum in place of the int Key. You could probably use glfwGetKeyName() to get the printable key name, however this resulted in exceptions for me when pressing some keys.
How to read key from keyboard in c++ ?
i used _getch() but this is not working always.
i heard about win32 keyboard api. i am targeting to windows so window specific technique is fine. can anyone give me simple example how to read key and check for arrow and function key.
i read article
How to simultaneous read keys on keyboard?
but this is not working in may case. here is my attempt inspired from above linked reference
char temp;
BYTE keys[256];
while(true)
{
temp = _getch();
if(GetKeyboardState(keys))
{
if(keys[VK_UP]&0xF0)
{
// Move Up : Case failing when i pressed up key
}
else if(keys[VK_DOWN]&0xF0 || keys[VK_RETURN]&0xF0)
{
// Move Down : Case failing when i pressed down or enter
}
else if(keys[VK_TAB]&0xF0)
{
// Move Next : Case failing when i pressed tab
}
else
{
// Print charecter which read using _getch()
cout<<temp;
}
}
}
i read MSDN article but do not understand what they are doing. i am doing such program first time so please make your example clear and illustrative so i can easly get it. thanks
I don't have a Windows machine at hand to test this out, but I am thinking that the fact that you are using temp = _getch(); before GetKeyboardState(keys) is eating your characters.
there are many library in C++ which handle this type of problem, if you are the choice, I advise you to use QKeySequence and other classes to let useful keyboard management.
If you want to see example, refer you to chromium project, here is an example used to test code of "keyboard driver".
you can either search many example with "filetype" syntax in google search engine (example : filetype:cc GetKeyboardState)...
you need to set correctly the layout before use GetKeyboardState...
Hope this help you.
Regards,
/Mohamed
Today I set up the input in my application for all the different keys. This works fine except for virtual keys, for example, caret or ampersand. Keys that normally need shift to be got at. Using SDL these virtual keys don't work. As in they do not register an event.
if (event.type == SDL_KEYDOWN) {
switch (event.key.keysym.sym) {
case SDLK_CARET:
Keys[KeyCodes::Caret] = KeyState::Down;
break;
case SDLK_UP:
Keys[KeyCodes::Up] = KeyState::Down;
break;
default:
break;
}
I am absolutely sure my system works with physical keys like Up. The program queries a keystate like so:
if (Keys[KeyCode] == KeyState::Down) {
lua_pushboolean(L, true);
} else {
lua_pushboolean(L, false);
}
KeyCode is passed in as an argument.
So why are virtual keys, or keys that need shift to get at not working using SDL's KeyDown event type? Is more code needed to get to them? Or am I being stupid?
SDL only reports real key events.
The good news is you can enable Unicode translation to get symbols like '^' or '#'.
First put this in your initialization code:
SDL_EnableUNICODE(1);
Now SDL_KEYDOWN events will have the accompanying character in the unicode member of SDL_keysym. This factors in shift, caps lock, etc., when translating the key press into a character. Keys like SDLK_UP will have unicode == 0.
This actually makes using keysym.unicode ideal for text input, especially when used with SDL_EnableKeyRepeat.
Here's an example: on my keyboard, I hold shift-6 to generate ^. The program recieves an SDL_KEYDOWN event with keysym.sym == SDLK_6, and keysym.unicode == '^'.
The one caveat is that only key press events will be translated, not release events. But this should not be a big problem, since you shouldn't use text characters for game controls anyway, only real keys. And if you're doing text input with key repeating, it only matters when keys are pressed, not released.
You might have to mix-and-match using keysym.sym and keysym.unicode to fit your exact needs.
Ok I do apologise for getting slightly frustrated but I have finally got some code to tell when some one has pressed on the Caret key for example. I do hope others find this useful information.
case SDLK_6:
if (event.key.keysym.mod == KMOD_LSHIFT || event.key.keysym.mod == KMOD_RSHIFT) {
Keys[KeyCodes::Caret] = KeyState::Down;
} else {
Keys[KeyCodes::n6] = KeyState::Down;
}
break;
Basically when checking normal keys that have a shift click special key then check the key modifier. I understand the unicode value now but this idea seems simpler for now.
Again thanks for all the help!
I'm in a situation whereby I am trying to read in a JSON config file which dictates what key commands map to given actions. For example:
...
{
"Action": "Quit",
"Combo" : "CTRL+Q"
},
...
Constructing a QKeySequence from the combo tag is trivial but I need to monitor QKeyEvents in order to trigger actions. Please note I have to monitor QKeyEvents because they are used for other purposes in the application as well. i.e. it would not be acceptable to only monitor key commands for QKeySequences (if that is even possible).
Short of writing a custom parser to construct a QKeyEvent object for each "Combo" tag, is there anyway of comparing a QkeyEvent to a QKeySequence? For example:
QKeyEvent KeyCommandsHandler::toKeyEvent(QKeySequence sequence) {
//somehow convert to QKeyEvent
}
In general, you cannot compare QKeyEvent and QKeySequence objects. QKeyEvent represents the event of a single key press or release, whereas a QKeySequence can contain a sequence of up to four keys, each with optional modifier information.
You can, however, compare the objects if you are sure that your key sequences will always contain just one key:
bool isEquiv(const QKeyEvent& event, const QKeySequence& seq)
{
if (seq.count() != 1)
return false;
return seq[0] == (event.key() | event.modifiers());
}
You can even write a conversion function for QKeyEvent to QKeySequence:
QKeySequence toKeySequence(const QKeyEvent& event)
{
return QKeySequence(event.key() | event.modifiers());
}
Note that it does not make sense to convert a QKeySequence to a QKeyEvent, though, since you have to choose a specific event type such as QEvent::KeyPress or QEvent::KeyRelease.
A simple solution (written in python):
key = QKeySequence(event.modifiers()|event.key()).toString()
Will give you the entire sequence in string form, such as "Ctrl+Q".
The benefits are (at least in python) that you can find in a dict of shortcuts, while a QKeySequence would not have been hashable.
Beware that this expects you use the correct typecase and spacing. "ctrl +Q" will not match. To avoid all issues, you can do the following when first reading the shortcuts:
shortcut = shortcut.lower().remove(' ')
and match/find using
key = QKeySequence(event.modifiers()|event.key()).toString().lower()
or better yet:
shortcut = QKeySequence(shortcut).toString()
and match directly.
A Qt4.7 note with code for converting KeyEvent to KeySequence. (But the code is flawed because it casts an int for the keycode from QKeyEvent.key() to a string. Better to use QKeyEvent.text() ?)
Also, the code in Ferdinand's answer:
QKeySequence(event.key() | event.modifiers())
is not type safe (mixes int and QKeyboardModifiers) and if converted to Python fails in PyQt, but not in PySide?
Also, "QKeyEvent represents the event of a single key press or release" doesn't really explain it. A QKeyEvent can tell you what combination of keys were down, just not the order in which they were pressed. When the user presses keys in sequence, your app might get a sequence of QKeyEvents (depending on whether your app is using default versus overridden handlers for QKeyEvent.) The later QKeyEvents will show you all the keys that were down at the time of the event. They might no longer be down. It is rather complicated.