Qt Gui Thread is blocking Issue - c++

Question

I'm junior programmer
recently, I have implemented grabbing of Image using Halcon library.
when I press live button, Timer start to grab image. it works but main screen freezes to the timer cycle.
so, I am improving performance grabbing of Image using Thread
first I implemented thread like this
[ImageUpdateWorker.h]
class ImageUpdateWorker : public QObject
{
Q_OBJECT
public:
explicit ImageUpdateWorker(QObject* parent = 0, QString strThreadName = "ImageUpdateWorker");
~ImageUpdateWorker();
signals:
void finished();
void grab();
public slots:
void run();
private:
bool m_bStop{ false };
};
[ImageUpdateWorker.cpp]
ImageUpdateWorker::ImageUpdateWorker(QObject* parent, QString strThreadName)
: QObject(parent)
{
setObjectName(strThreadName);
}
ImageUpdateWorker::~ImageUpdateWorker()
{
}
void ImageUpdateWorker::run()
{
while (m_bStop == false)
{
emit grab();
}
emit finished();
}
second I implemented inherited QWidget UI Widget with output Screen like this
m_pThread = new QThread();
m_pUpdateWorker = new ImageUpdateWorker(nullptr, strName);
m_pUpdateWorker->moveToThread(m_pThread); // UpdateWorker move to Thread
connect(m_pThread, SIGNAL(started()), m_pUpdateWorker, SLOT(run()));
connect(m_pThread, SIGNAL(finished()), m_pThread, SLOT(deleteLater()));
connect(m_pUpdateWorker, SIGNAL(finished()), m_pThread, SLOT(quit()));
connect(m_pUpdateWorker, SIGNAL(finished()), m_pUpdateWorker, SLOT(deleteLater()));
connect(m_pUpdateWorker, SIGNAL(grab()), this, SLOT(onGrab()));
when I call "m_pThread->start();" screen starts to blokcing :(
If you have any advice or information, I would appreciate it. thank you for reading.

Answer 1

Use m_pImageUpdateThread->moveToThread(m_pThread);

Answer 2

I don't know in QT.
I sent you the code I used in C#.
Mainly you must use the delegates if you don't want to freeze the GUI.
hdisplay is the object HalconDotNet:HWindowControlWPF.
camera is a class where I define the camera parameters.
inside camera.Grab there is the code:
HOperatorSet.GrabImage(out ho_Image, _AcqHandle);
h_Image = new HImage(ho_Image);
At the initialization there is the code:
// Initialise the delegate
updateLiveDelegate = new UpdateLiveDelegate(this.UpdateLive);
HImage ho_Image = new HImage();
Here the code I use:
// ==================
// LIVE
// ==================
bool stopLive = true;
// Declare the thread
private Thread liveThread = null;
// Declare a delegate used to communicate with the UI thread
private delegate void UpdateLiveDelegate();
private UpdateLiveDelegate updateLiveDelegate = null;
private void btnLive_Click(object sender, RoutedEventArgs e)
{
try
{
stopLive = !stopLive;
// if stopLive = false, live camera is activated
if (!stopLive)
{
// Launch the thread
liveThread = new Thread(new ThreadStart(Live));
liveThread.Start();
}
}
catch (Exception ex)
{
// Error
}
}
private void Live()
{
try
{
while (stopLive == false)
{
if (camera.Grab(out ho_Image))
{
// Show progress
Dispatcher.Invoke(this.updateLiveDelegate);
}
else
{
// No grab
stopLive = true;
}
}
// here stopLive is true
}
catch (Exception ex)
{
// Error
}
}
private void UpdateLive()
{
try
{
int imageHeight;
int imageWidth;
string imageType;
ho_Image.GetImagePointer1(out imageType, out imageWidth, out imageHeight);
hDisplay.HalconWindow.SetPart(0, 0, imageHeight - 1, imageWidth - 1);
// display
hDisplay.HalconWindow.DispImage(ho_Image);
}
catch (Exception ex)
{
// Error
}
}