[SOLVED] QT MainWindow freezes when closing OpenCV Webcam Window - new QT Window outside MainWindow

? Offline

I get my images from a run loop within this CLEyeCameraCapture class in a defined fps rate. I would like to parse the signal of this runloop to any QT Window eg. pseudo:

@run(){
while(runnig){

iplimage = getImage(Camera);
QImage = IPLtoQimage(iplimage);
newwindow.show(QImage);
}
}@

I am thinking now that the cleanest way to do that would be to create a newWindow in the mainWindow .cpp and then access this window in my QObject class (which inherits the run loop and camera access).

But i lack of experience to find the right expressions.

SGaist

Then I would recommend taking a look at the "MandelBrot example":http://qt-project.org/doc/qt-4.8/threads-mandelbrot.html

? Offline

hey SGaist, thanks for the info but i already got the whole loop and my problem is just to connect the image created in the loop with the QDialog (parent) of the class.

I took a look at this:

http://www.sobbayi.com/blog/software-development/access-members-parent-class-qt-c/

which kind of is what I'm searching. it works ok except i cannot see the image due to i made something wrong with the label.

in my child class this compiles fine:

@ while(_running)
{
CLEyeCameraGetFrame(_cam, pCapBuffer);

// Resize Image to fit screen size
cvResize(pCapImage,resizedpCapImage,CV_INTER_NN);
cvShowImage(_windowName, resizedpCapImage);

*qimg = IplImage2QImage(resizedpCapImage);

parentqlabel->setPixmap(QPixmap::fromImage(*qimg));
parentqlabel->show();@

but does not show the image

SGaist

The technique described in this article is exactly what is discouraged to do in general. The basic idea with Qt is to emit a signal from the child class that the parent class connects to. So the child class doesn't need to know anything about the parent (keeps the code clean). Or if you don't want a signal (in a dialog case) you use getters once your done with the dialog.

Back to your problem, you are using an infinite loop in the main thread so this will block everything, hence the mandlebrot example.

Also why make qimg a pointer ? You don't need that, just make in a regular QImage. You will avoid memory management problem.

? Offline

I get that its discouraged and i get that this is not pro's programming here but I need to get it to work asap so I'm willing to take hate :)

In my CameraCapture class i declared the variable like the following, if you can point me out the correct way it would be nice. As I mentioned I am a C++ starter.

@ QImage *qimg = new QImage();

//Create Buffer for pCap
PBYTE pCapBuffer = NULL;

// Create camera instance
_cam = CLEyeCreateCamera(_cameraGUID, _mode, _resolution, _fps);
if(_cam == NULL)
...
...
...

// Start capturing
CLEyeCameraStart(_cam);
cvGetImageRawData(pCapImage, &pCapBuffer);
// image capturing loop
while(_running)
{
CLEyeCameraGetFrame(_cam, pCapBuffer);

// Resize Image to fit screen size
cvResize(pCapImage,resizedpCapImage,CV_INTER_NN);
cvShowImage(_windowName, resizedpCapImage);

*qimg = IplImage2QImage(resizedpCapImage);@

Also, as you complained the child process and parent process might be switched here, so I guess I could make the CaptureClass parent of the CameraWindow Class which would leed to:

MainWindow (QMainWindow) --> creates CaptureObject (QObject)
CaptureObject (QObject) -> creates and is parent of CameraWindow (QDialog)

This is the only solution I can think of as I see that I have thread problems because I can not create communication between CaptureObject and Camera Window now.

@ parentqlabel->setTextFormat(Qt::RichText);
parentqlabel->setText("textest");@

creates

ASSERT failure in QCoreApplication::sendEvent: "Cannot send events to objects owned by a different thread. Current thread 48cb8f8. Receiver '' (of type 'QLabel') was created in thread 23c0790", file kernel\qcoreapplication.cpp, line 535
ASSERT failure in QCoreApplication::sendEvent: "Cannot send events to objects owned by a different thread. Current thread 23c0790. Receiver '' (of type 'QTextDocument') was created in thread 48cb8f8", file kernel\qcoreapplication.cpp, line 535

This is because the CameraCaptureSDK provided code creates a thread :

@_hThread = CreateThread(NULL, 0, &CLEyeCameraCapture::CaptureThread, this, 0, 0);@

...
@
DWORD WINAPI CLEyeCameraCapture::CaptureThread(LPVOID instance)
{
// seed the rng with current tick count and thread id
srand(GetTickCount() + GetCurrentThreadId());
// forward thread to Capture function
CLEyeCameraCapture *pThis = (CLEyeCameraCapture *)instance;
pThis->Run();
return 0;@

? Offline

ok so i put my new window as part of the cameracapture class and it opens and closes...wonderfull, but MainWindow GUI freezes again when hitting the close button on it to close my window.

here i am..back at the beginning

SGaist

That's exactly why I suggested the mandelbrot example, you have there an example of how to implement an forever loop and interact with your application.

You can't update GUI elements from outside the main thread.

Could you post a link to the sdk ?

? Offline

Here are the links:

http://codelaboratories.com/research/view/cl-eye-platform-cpp-sample

http://codelaboratories.com/get/cl-eye-sdk/

the window now closes (typing mistake) correctly. (yeij)

so now if i do this:

@CameraWindow::CameraWindow(QWidget *parent)
: QDialog(parent)
{
ui.setupUi(this);
imageLabel = new QLabel(this);
imageLabel->setTextFormat(Qt::RichText);
imageLabel->setText("textest");
}

CameraWindow::~CameraWindow()
{

}
@

and create a window within my capture class this opens correctly and text is displayed. but if i try to make this a function

@CameraWindow::CameraWindow(QWidget *parent)
: QDialog(parent)
{
ui.setupUi(this);
imageLabel = new QLabel(this);
}

CameraWindow::~CameraWindow()
{

}

void CameraWindow::dispText(){
imageLabel->setTextFormat(Qt::RichText);
imageLabel->setText("textest");
}@

and call camerawindow->dispText() from my capture class i get a "Cannot create children for a parent that is in a different thread" which is akward because obviously imageLabel should be an instance within my CameraWindow not anything else. as CameraWindow is created within this class i really wonder what's going on :)

To your remark: Even if i create a dialog within another thread (obviously another thread because it says so) the GUI Element QLabel i create within this new dialog can only be updated in my MainWindow thread?

If I understand you pointing to the mandelbrot example the solution would be to exchange the orignal sdk thread:

@HANDLE _hThread@

@_hThread = CreateThread(NULL, 0, &CLEyeCameraCapture::CaptureThread, this, 0, 0);@

with another QT Thread creation...

@
RenderThread::RenderThread(QObject *parent)
: QThread(parent)

@

which is kind of what i do not feel capable of :)

SGaist

Creating widgets outside the main thread is also forbidden.

Here is a rough idea on how to use a subclassed QThread to get the data from the camera and send them to your widget. (Just the run function actually but it's the most important)

@
void MyQThread::run()
int w, h;
IplImage *pCapImage;
PBYTE pCapBuffer = NULL;

    // Create camera instance
    _cam = CLEyeCreateCamera(_cameraGUID, _mode, _resolution, _fps);
    if(_cam == NULL)        return;
    // Get camera frame dimensions
    CLEyeCameraGetFrameDimensions(_cam, w, h);

// Depending on color mode chosen, create the appropriate OpenCV image
if(_mode == CLEYE_COLOR)
pCapImage = cvCreateImage(cvSize(w, h), IPL_DEPTH_8U, 4);
else
pCapImage = cvCreateImage(cvSize(w, h), IPL_DEPTH_8U, 1);

    // Set some camera parameters
    CLEyeSetCameraParameter(_cam, CLEYE_GAIN, 20);
    CLEyeSetCameraParameter(_cam, CLEYE_EXPOSURE, 511);
    CLEyeSetCameraParameter(_cam, CLEYE_ZOOM, (int)(GetRandomNormalized()*100.0));
    CLEyeSetCameraParameter(_cam, CLEYE_ROTATION, (int)(GetRandomNormalized()*300.0));

    // Start capturing
    CLEyeCameraStart(_cam);
    // image capturing loop
    while(_running)
    {
        cvGetImageRawData(pCapImage, &pCapBuffer);
        CLEyeCameraGetFrame(_cam, pCapBuffer);
         emit capturedImage(IplImage2QImage(pCapImage));
    }
    // Stop camera capture
    CLEyeCameraStop(_cam);
    // Destroy camera object
    CLEyeDestroyCamera(_cam);
    _cam = NULL;
}

@

Depending on the image format you could even directly capture to a QImage avoiding the conversion.

Hope it helps

? Offline

thank you so much for your answers and your advice.
i'll try to implement this with looking at the mandelbrot example and post updates here.

? Offline

I followed the mandelbrot example and did alike with my class.

Now, I am not able to acces wait(), start(), isRunning() or any other static (protected?) function which seems either not to be declared or not found.

I included the following, something's missing ?
@
#include <QCoreApplication>
#include <QThread>
#include <QObject>
#include <QMutex>
#include <QWaitCondition>
@

ok...it seems that this is because i create a dialog window within the render thread that seems not to be able to parent correctly.

i guess the way would be to open the camerwindow dialog within the mainwindow class and connect the signal of the renderthread to the camerwindow ?

SGaist

Did you subclass QThread and use the code in the run function ?

No widget stuff whatsoever in another thread than the GUI thread (they mean it)

That would be one way yes

? Offline

Ok, seems that something is wrong with the connection:

@1>.\camerawindow.cpp(14) : error C2664: 'bool QObject::connect(const QObject *,const char *,const QObject *,const char *,Qt::ConnectionType)': Konvertierung des Parameters 1 von 'RenderThread **' in 'const QObject *' nicht möglich
1> Die Typen, auf die verwiesen wird, sind nicht verknüpft; die Konvertierung erfordert einen reinterpret_cast-Operator oder eine Typumwandlung im C- oder Funktionsformat.@

although i defined RenderThread as in the example..

@class RenderThread : public QThread
{
Q_OBJECT
@

SGaist

it seems that you are giving the address of the pointer to your RenderThread.

Do you have something like that :

@RenderThread *renderThread = new RenderThread;
conncet(&renderThread, etc....)@

?

? Offline

thanx, i'm tryin hard to get this to work ;)
it's really chaos now..

SGaist

The best is to go one step at a time, first get the data from the camera, then add the widget etc... Trying to make all at the same time is recipe for failure

? Offline

going with your version didn't work out so i went with this:

camerawindow.cpp:

@CameraWindow::CameraWindow(QWidget *parent)
: QDialog(parent)
{
ui.setupUi(this);
QLabel *imageLabel = new QLabel(this);

qRegisterMetaType<QImage>("QImage");
connect(&thread, SIGNAL(renderedImage(QImage)),
this, SLOT(updatePixmap(QImage)));

setWindowTitle(tr("multithread"));
}

...

int CameraWindow::startCaptureThread(){
this->show();

RenderThread *thread = new RenderThread(this, windowName, guid, CLEYE_COLOR_RAW, CLEYE_VGA, 50);

thread->StartCapture("abc");
}
@

which seems to work fine as looping the run() while loop correctly,

but obviously the updatePixmap function is never called so the objects might be mislinked or created in wrong syntax... frustrating ;)

? Offline

i tried with another connection:

@ connect(&thread, SIGNAL(sendText(std::string)),
this, SLOT(debugSomething(std::string)));@

@void CameraWindow::debugSomething(std::string something){
QString somethings(something.c_str());
qDebug()<<somethings;
}@

renderthread.cpp:
@while(_running)
{
emit sendText(text);
}@

and this as well seems not to emit anything or not correctly connect to the qdialog. why is this not working as it should ?

SGaist

You should replace all std::string with QString, that will avoid you some problems.
Your while loop might be a bit short and might block the main thread.

If your code is not top secret, could you share it i.e. via gitorious/github/other vcs service ? That might make things easier to look at

? Offline

Hi SGaist,

after getting a bit tired refitting the Mandelbrot Example to my needs I asked this question at StackOverflow. It turns out that there are some issues the way the example uses threads. I don't know if I could have saved my code but I was getting depressed so I recoded the way somebody pointed me out at StackOverflow and this worked instantly and also avoids image conversion as i can use the opencv namendWindow.

@//create new thread
QThread* thread = new QThread;

//init camera with guid, raw color capture, vga format and 50fps
cameraCapture = new CLEyeCameraCapture(winName, folder, userID, guid, CLEYE_COLOR_RAW, CLEYE_VGA, 50);
cameraCapture->moveToThread(thread);

connect(thread, SIGNAL(started()), cameraCapture, SLOT(StartCapture()));
connect(cameraCapture, SIGNAL(finished()), thread, SLOT(quit()));
connect(cameraCapture, SIGNAL(finished()), cameraCapture, SLOT(deleteLater()));
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
connect(ui.pushButton_startLogging, SIGNAL ( clicked() ),this,SLOT( activateLogging() ) );
connect(ui.pushButton_stopLogging, SIGNAL ( clicked() ),this,SLOT( deactivateLogging() ) );
@

I tried to follow this "example.":http://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/

Here is the "Question on SO.":http://stackoverflow.com/questions/18594528/create-thread-in-qdialog-and-emit-signals-to-qdialog-in-qt

Thank you for your help. Now i avoided the freezes. It might be of interest for people who using any conversion from IplImage to QImage: non of the conversions are fast enough for realtime (I did not measure wether the conversion or the displaying method is slowing down the process).

Thank you anyway for your help. I guess it is wise for anybody who rebuilds this to use their original code and put it in a Worker which then gets moved to a QThread.