Asynchronous drawing problems



  • I have one thread that reads image data from an external API. This image data I want to draw in an Qt application. I have created a widget to draw the image. The thread calls MyWidget::setPicture. However I get lots of strange X server errors, so I'm guessing something is not threads safe. Any tips on how to do this?

    @
    class MyWidget : public QWidget
    {
    Q_OBJECT
    public:
    MyWidget(QWidget *parent = 0);
    ~MyWidget();

    QPixmap pixmap;
    void setPicture(QImage);
    

    protected:
    void paintEvent(QPaintEvent *event);

    };
    @

    @
    void MyWidget::paintEvent(QPaintEvent */event/) {
    QPainter painter(this);
    painter.drawPixmap(this->rect(),pixmap);
    }

    void MyWidget::setPicture(QImage i){
    pixmap=QPixmap::fromImage(i);
    update();
    qApp->processEvents();
    }

    @



  • Why do you call @qApp->processEvents();@? And can you show code block where thread calls setPicture



  • You have to call the QWidget methods inside the main thread. I think that is your problem. If MyWidget::setPicture is a slot, you can call it by QObject::invokeMethod(...Qt::QueuedConnection) to call from your thread to the main thread.


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