How can I read QPixmap from QBuffer ?

onurcevik

I am trying to read image from a buffer and display it on QGraphicsView. The reason I am doing this because I am trying to implement a UDP image streaming program.

With the code below I am trying to capture image to the buffer and then read image from buffer to display it.

    QObject::connect(cap, &QCameraImageCapture::imageCaptured, [=] (int id, QImage img) {
        QByteArray buf;
        QBuffer buffer(&buf);
        buffer.open(QIODevice::WriteOnly);
        img.save(&buffer, "BMP");

        QPixmap *pixmap = new QPixmap();
        pixmap->loadFromData(QPixmap::loadFromData(buffer.buffer()));
        scene->addPixmap(*pixmap);


    });

But it gives this error:

error: cannot call member function 'bool QPixmap::loadFromData(const QByteArray&, const char*, Qt::ImageConversionFlags)' without object
       pixmap->loadFromData(QPixmap::loadFromData(buffer.buffer()));
                                                                 ^

Can you help me with this ?

onurcevik

I realised I was nesting two objects with this code:

pixmap->loadFromData(QPixmap::loadFromData(buffer.buffer()));

I edited my code like this and solved my problem.

    QPixmap *pixmap = new QPixmap();
    pixmap->loadFromData(buffer.buffer());
    scene->addPixmap(*pixmap);

Christian Ehrlicher

QPixmap::loadFromData is not a static function so you'll need an object. The whole stuff is also not needed - why do you save a QImage in a QBuffer just to load it again into a QPixmap?

QObject::connect(cap, &QCameraImageCapture::imageCaptured, [this] (int id, const QImage &img) {
  scene->addPixmap(QPixmap::fromImage(img));
}

onurcevik

@Christian-Ehrlicher The reason I save QImage to Buffer and load it again QPixmap is I am trying to implement a UDP image streaming program like I stated in my question above. So I am testing if I can load/read images then I'll try to implement UDP socket part.

So your code doesn't help me at all :) . You are loading QImage not reading it from buffer.

Christian Ehrlicher

@onurcevik said in How can I read QPixmap from QBuffer ?:

So your code doesn't help me at all :)

Maybe not my code but my comment:

QPixmap::loadFromData is not a static function so you'll need an object.

onurcevik

@Christian-Ehrlicher How can I use object in this code ? Should I create QPixmap Object to access it ? Can you show it with code ?

Christian Ehrlicher

@onurcevik said in How can I read QPixmap from QBuffer ?:

How can I use object in this code ?

QPixmap pm;

onurcevik

I realised I was nesting two objects with this code:

pixmap->loadFromData(QPixmap::loadFromData(buffer.buffer()));

I edited my code like this and solved my problem.

    QPixmap *pixmap = new QPixmap();
    pixmap->loadFromData(buffer.buffer());
    scene->addPixmap(*pixmap);

Christian Ehrlicher

@onurcevik said in How can I read QPixmap from QBuffer ?:

QPixmap *pixmap = new QPixmap();

And where do you delete this? Now you've a classic memleak. It's not needed to create it on the heap at all...