绘画QWidget外部GUI线程的问题 [英] Painting Issue on QWidget outsite GUI thread

问题描述

我正在开发一个应用程序，其中我想从远程主机连续接收图像，并在我的屏幕上显示它们。为此我遵循给定的策略
1）我有一个主要的QWidget对象包含QImage它（工作正常）
2）从远程主机接收的图像绘在QImage对象，这项工作使用QPainter在工作线程中完成。 （工作正常）
3）但问题是图像不更新QWidget，除非我调整窗口小部件的大小，因为重绘事件被调用QWidget ...现在如果我从工作线程重新绘制QWidget它会给出错误QPixmap：在GUI线程之外使用pixmaps不安全和应用程序崩溃。

I am developing an appliation in which I want to continuously receive images from remote host and display them on my screen. for this I am following the given strategy 1) I have a main QWidget object which contains the QImage on it (works fine) 2) Images received from remote host are painted on QImage object, this work is done in a worker thread using QPainter. (works fine) 3) but the problem is that the image is not updated on QWidget, unless I resize the widget, because the repaint event is called for QWidget... Now if i repaint the QWidget from the worker thread it gives error "QPixmap: It is not safe to use pixmaps outside the GUI thread".. and application crashes.

有关这方面的任何帮助吗？

Any help regarding this?

推荐答案

使用 QueuedConnection

发出工作线程的信号

Emit a signal from the worker thread with a QueuedConnection
or post an update event (QPaintEvent) to the widget from the worker thread.

//--------------Send Queued signal---------------------
class WorkerThread : public QThread
{
    //...
signals:
    void updateImage();

protected:
    void run()
    {
        // construct QImage
        //...
        emit updateImage();
    }
    //...
};

//...
widgetThatPaintsImage->connect(
    workerThread, 
    SIGNAL(updateImage()), 
    SLOT(update()),
    Qt::QueuedConnection);
//...

//--------------postEvent Example-----------------------
class WorkerThread : public QThread
{
    //...
protected:
    void run()
    {
        //construct image
        if(widgetThatPaintsImage)
        {
            QCoreApplication::postEvent(
                widgetThatPaintsImage, 
                new QPaintEvent(widgetThatPaintsImage->rect()));
        }
        //... 
    }

private:
    QPointer<QWidget> widgetThatPaintsImage;
};

不要忘记同步对图片的访问。

作为同步的替代方法，您还可以将图像发送到gui主题，例如 Mandelbrot示例。

Don't forget to synchronize the access to the image.
As an alternative to the synchronization, you could also send the image to the gui thread, like in the Mandelbrot Example.

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