QWidget::repaint: Recursive repaint detected

Xav12358

Hello,

I use a QWidget in a Qthread and I had to modify the image in a Qlabel of multiple object.
The problem is when I modify the image inside the Qlabel the update of image works bad.

I ha to use repaint fonction to force th label to update regulary the display. But most of the time I have this error:

QWidget::repaint: Recursive repaint detected

How Can I force a update of the label without create a recursive repaint?

SGaist

Hi,

One thing that is wrong here: updating widgets outside the GUI thread is a no go.

What exactly are you doing ?

Xav12358

@SGaist In fact I have a blocking process, this is the reason why I must put a partof my process in a Qthread.
That Qthread process had to update a list a Qlabel image and display it. The problem if I don't use repaint event the label doesn't refresh dynamically, it waits the last image to update its content.

So I use repaint and to avoid a recursive repaint error I made that:

    void paintEvent(QPaintEvent *event)
    {
        qDebug() << "GLWidget::paintEvent In";
        if(!paintingActive())
            QWidget::paintEvent(event);
        qDebug() << "GLWidget::paintEvent Out";
    }

But it don't seems to work, I still have the same error.

SGaist

Again: don't do GUI changes to widgets from other threads

Use signals and slots to update your labels, you may need a class like QSignalMapper. Depending on how you get/generate the images, the Mandelbrot example would likely be useful.

Xav12358

Is it possible to have a QSignalMapper like this:

My QThread send a signal (emit newImage(QImage,int) connect to my object ImageWidget (slot(void newImage(Qimage)) ?

SGaist

Did you read the class documentation ? It doesn't work like that.

Anyway, can you describe more precisely your setup ?

Xav12358

How should I emit a signal from a QThread?

Here is the code I use:

class BGEPreviewWorker : public QObject
{
    QHash<QString,GLWidget*> hashWidgetView; ///< list of display data

    Q_OBJECT
    int iwidth_;            ///< memorise the with of element to process
    int iheight_;           ///< memorise the height of element to process

    cv::Mat dx1_blur1;
    double min,max;


    QHash<QString,GLWidget*> hashWidgetView; ///< list of display data
public:

    BGEPreviewWorker(QObject *parent = NULL);
    ~BGEPreviewWorker();

    ///
    /// \brief display function which collct all data in the gpu and display it
    ///
    void display();



public slots:
    void work();
    void askToClosed(QString);

signals:
};


BGEPreviewWorker::BGEPreviewWorker(QObject *parent):
    QObject(parent),
    iwidth_(1920),
    iheight_(1080),
    bIsRunning_(false),
    bIsInitialised_(false)
{




    dx1_blur1.create(iheight_,iwidth_,CV_64F);

    hashWidgetView["save_Blur1"]        = new GLWidget(iwidth_,iheight_,GLWidget::BGE_64F,0);



    QHash<QString,GLWidget*>::iterator iter = hashWidgetView.begin();
    for(int i = 0;
        i<hashWidgetView.size();
        i++)
    {
        connect(this,SIGNAL(newImage(ImageUpdater)),((iter+i)).value(),SLOT(newImage(ImageUpdater)));
        


        (iter+i).value()->show()

    }

}

BGEPreviewWorker emit a signal (newImage) to the corresponding GLWirdget.
Here how I use BGEPreviewWorker:

  BGEPreviewWorker *BGEWork = new BGEPreviewWorker();
   QThread*  BGEThread = new QThread();
    BGEWork->moveToThread(BGEThread);

    connect(BGEThread, SIGNAL(started()), BGEWork, SLOT(work()) );

jsulm

@Xav12358 It doesn't matter whether you're in another thread or not: emitting signal is always same:

emit mySignal();

Just use QueuedConnection when connecting signal and slot.