Capture screenshot not working (Qt 5.4) Linux Yocto

gmahan

Hi,

I'm trying to capture a screenshot in PNG of my device that is running a custom Yocto linux build. When I run the application I get no value in the byteArray that contains the image. The code works fine on my Fedora Linux workstation.

The code is as follows:

@void Utils::GetScreenBase64String(QByteArray &bArray)
{

QScreen *screen = QGuiApplication::primaryScreen();

if (screen)
{
    QPixmap pixmap = QPixmap(); // Create a new pixmap
    pixmap = screen->grabWindow(0); // Grab the screenshot

    bArray.clear(); // Clear the byte array

    QBuffer buffer(&bArray);

    buffer.open(QIODevice::WriteOnly);
    pixmap.save(&buffer, "PNG");
    buffer.close();

    bArray = bArray.toBase64();
}

}@

I have also tried the following :

@void Utils::GetScreenBase64String(QByteArray &bArray)
{

QScreen *screen = QGuiApplication::primaryScreen();

if (screen)
{
    QWindow window;
    QPixmap pixmap = QPixmap(); // Create a new pixmap
    pixmap = screen->grabWindow(window.winId()); // Grab the screenshot

    bArray.clear(); // Clear the byte array

    QBuffer buffer(&bArray);

    buffer.open(QIODevice::WriteOnly);
    pixmap.save(&buffer, "PNG");
    buffer.close();

    bArray = bArray.toBase64();
}

}@

bArray in both cases is returned empty. Not sure if I am missing some kernel library. Any help would be appreciated.

Thanks!

agocs

QScreen::grabWindow is useless when not running on an actual windowing system. On embedded it is simply not implemented.

For Qt Quick apps, use QQuickWindow::grabWindow() instead.

gmahan

Thanks for replying to this. I added the QQuickWindow module to the file and to the .pro (quick) file. But I now run into the following issue on compile time:

/home/gmahan/Qt5.4.0/5.4/gcc_64/include/QtGui/qopengl.h:122: error: GL/gl.h: No such file or directory

include <GL/gl.h>

Not sure what's causing this. Sorry, I'm relatively new to Qt.

agocs

Hmm you are missing OpenGL support. Then your apps are QWidget-based, I guess? In that case try something like http://doc-snapshot.qt-project.org/qt5-5.4/qwidget.html#render

gmahan

I changed the function to use QWidget.render(), but all I get is a blank screen as the image.

@void Utils::GetScreenBase64String(QByteArray &bArray, QWidget *widget)
{

QScreen *screen = QGuiApplication::primaryScreen();

if (screen)
{
    QPixmap pixmap(widget->size()); // Create a new pixmap
    widget->render(&pixmap);

    //pixmap = screen->grabWindow(WindowId::GetCurrentWinId()); // Grab the screenshot

    bArray.clear(); // Clear the byte array

    QBuffer buffer(&bArray);

    buffer.open(QIODevice::WriteOnly);
    pixmap.save(&buffer, "PNG");
    buffer.close();

    bArray = bArray.toBase64();
}

}
@

gmahan

The above code worked fine on my workstation running Linux, I was not capturing the entire base64 string when trying to decode. I need to run on my embedded device to see if it works fine.