QopenglWidget share context among thread

Delavega77

I create a QOpenglWidget and I'm trying to share context in a WorkerThread to load textures:
void VideoWidget::updateVideoFrame(QVideoFrame frame)
{
QOpenGLContext* ctx = new QOpenGLContext();
QOpenGLContext* sharectx = QOpenGLContext::currentContext();
ctx->setFormat(sharectx->format());
ctx->setShareContext(sharectx);
ctx->create();
if (ctx->isValid()){

    qDebug()<<"valid";
}
WorkerThread *workerThread = new WorkerThread();
ctx->moveToThread(workerThread);
connect(workerThread,SIGNAL(resultReady(QOpenGLTexture*)), this, SLOT(updateTexture(QOpenGLTexture*)));
connect(workerThread, &WorkerThread::finished, workerThread, &QObject::deleteLater);
workerThread->setFrame(frame);

workerThread->start();
}

here it is workerthread.h

class WorkerThread : public QThread
{
Q_OBJECT

void run() override {
    //    Q_UNUSED(frame);

    // Handle the frame and do your processing
    QVideoFrame cloneFrame(frametexture);
    cloneFrame.map(QAbstractVideoBuffer::ReadOnly);
    QImage image(cloneFrame.bits(),
                 cloneFrame.width(),
                 cloneFrame.height(),
                 QVideoFrame::imageFormatFromPixelFormat(cloneFrame.pixelFormat()));


    QOpenGLTexture* texture = new QOpenGLTexture(image);

    cloneFrame.unmap();

}

But when i try to create the texture there is no valid context.
What I'm missing?
thanks

Delavega77

This post is deleted!

Christian Ehrlicher

The thread is stopped (and deleted in your case since your signals/slot connection) as soon as run() finishes which is pretty fast in your case...
The signal resultReady is also not emitted anywhere

Delavega77

@Christian-Ehrlicher
thank you for the reply, the signal is received correvtly in the main thread. but when i cretae the opengltexture the context is not valid

Christian Ehrlicher

The signal resultReady() is not sent in your example so I guess it's incomplete.

Delavega77

@Christian-Ehrlicher you are right copy/paste error but i sent the signal right the unmap of the frame.
But it gives error when create the opengltexture because the context is not valid

Christian Ehrlicher

And where do you use the QOpenGLContext created in updateVideoFrame()? Did you check that the generated QImage is valid?

Delavega77

@Christian-Ehrlicher
the image is correct i also save it on hdd and it is fine.
in the updatevideoframe i just create the context share it and move the thread. Maybe do i need something else?

Christian Ehrlicher

I've no more idea but I think you don't need a context at all. From the QOpenGLTexture ctor description:

This does create the underlying OpenGL texture object. Therefore, construction using this constructor does require a valid current OpenGL context.

Maybe also check for QOpenGLTexture::isCreated() in thread and main thread.
And I wonder if you need a thread for this small calculation at all - since not much is done the thread overhead looks much bigger than the benefit.

Delavega77

@Christian-Ehrlicher i know that the qopenglwidget creates the underlying context and it is shared among all the others widget and it works because i used it.
but for documentation to use context in a different thread i have to use share context but...

wrosecrans

I use

    QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts);

before I create my QApplication in main to make sure all contexts are sharing by default. I had some trouble getting sharing to work after porting some code from QGLWidget to QopenGLWidget a few years back, and that was the bit that got everything working for me.