Updating multiple QImages on QML::Image view displays only the last one sent

Question

I have Image qml component to display QImages. Following is the QML code for it.

Code:

Item {

    Image {
       id: my_qimage_viewer
       anchors.fill: parent
    }

    Connections {
        target: qimage_selector_cpp_backend
        onQImageDisplayRequested: {
            my_qimage_viewer.source = next_qimage_source
            console.log("New qimage sent for display is : " + my_qimage_viewer.source)
        }
    }

}

What is working:
I have a C++ class using QQuickImageProvider to supply QImages with different IDs every time.

This technique basically works if I update single QImages on selection of some button by user. I can generate a QImage on the fly & update it on my_qimage_viewer. Also able to display multiple different images on demand from user. This proves that my technique using QQuickImageProvider is basically working.

What is not working
But, here is where the problem arises. when I send many QImages subsequently, like 50-60 of them all in a for loop, then it does not display all but only displays the last one sent for update !

My objective here is to try play 50-60 QImages with some millis gap in between to make them appear like a video/animation. Is it that the Image component is not made for such kind of use? Or is it that I am doing some mistake?

Question:
May be I should wait for each QImage to be display complete before updating the next? How can I do that if that is whats missing?

Is there an example of an app using Image to display multiple QImages making it appear like a video or animation?

The answer depends on when you want to update the images, or do you want them to be only consecutive ?, that is, there is only the delay to load the image or is doing a construction and / or processing of the image — eyllanesc, Dec 25 '17 at 00:30
@eyllanesc I want to update all the images consecutively. Yes. there will be delay in construction of the image. But before trying with processed `QImage`s, I firstly decided to try out plain simple `QImage`s created on the fly. This is firstly to prove the framework actually works. Is there a standard example of updating multiple `QImage`s on to a [QML::Image](https://doc-snapshots.qt.io/qt5-dev/qml-qtquick-image.html) ? — TheWaterProgrammer, Dec 25 '17 at 08:56

score 1 · Accepted Answer · answered Dec 25 '17 at 15:29

if you use a for-loop you do not give time to show and update the images, you should give a little time between each image.

Assuming that the acquisition time of the image is less than a certain value, for example less than 1/60 seconds we could use a NumberAnimation setting in an appropriate step:

Window {
    visible: true
    width: 640
    height: 480

    Image {
        property int number
        id: name
        source: "image://numbers/"+number

        NumberAnimation on number {
            from:0
            to: 60
            duration: 1000
        }
    }
}

imageprovider.h

#ifndef IMAGEPROVIDER_H
#define IMAGEPROVIDER_H

#include <QQuickImageProvider>
#include <QPainter>
#include <QTime>

class ImageProvider : public QQuickImageProvider
{
public:
    ImageProvider():QQuickImageProvider(QQuickImageProvider::Image){
        qsrand(QTime::currentTime().msec());
    }
    QImage requestImage(const QString &id, QSize *size, const QSize &requestedSize){
        int width = 100;
        int height = 50;
        if (size)
            *size = QSize(width, height);
        QImage img(requestedSize.width() > 0 ? requestedSize.width() : width,
               requestedSize.height() > 0 ? requestedSize.height() : height, QImage::Format_RGB32);
        img.fill(QColor(qrand() % 256, qrand() % 256, qrand() % 256));
        QPainter painter(&img);
        painter.setRenderHint(QPainter::Antialiasing, true);
        painter.drawText(QRectF(QPointF(0, 0), img.size()),  Qt::AlignCenter,
                         QTime::currentTime().toString("hh:mm:ss.z")+" "+id);
        painter.end();
        return img;
    }
};

#endif // IMAGEPROVIDER_H

A complete example can be found in the following link

thanks a lot for this answer. this was really helpful for me to understand this way of using `QtQuickImageProvider` in case of multiple QImages — TheWaterProgrammer, Dec 25 '17 at 23:32

Updating multiple QImages on QML::Image view displays only the last one sent

1 Answers1