QT QGL Black Widget on different pc

Question

I wrote a small program for change blindness (this time windows only). It displays 4 images (2 real, 2 grey) via open gl in a qgl widget. It uses painters to do it.

It works quite on my pc. I tried to put it onto an other without qt and placed this gl files into the directory (found the with dependency walker):

libgcc_s_dw2-1.dll mingwm10.dll QtCore4.dll QtGui4.dll QtOpenGL4.dll

It worked well on my pc, outside the QTCreator and without any path set. On each other pc the QGL widgets are just black. The program works normaly (click on button etc) but all images are just black. I looked for the paths but they are all fine. No idea whats happening. The pcs I used have older hardware but nothing to special (older Ati cards with older driver, but i could play Half Life 2 on mid settings, so I assume the drivers are installed).

I got no error message or anything. Any Idea what can be done to fix it? If nothing works I will try to create an ubuntu usb stick with this program in it.

Paths (the paths are correct):

C:\tina_and_mona\pics\1\1.jpg C:\tina_and_mona\pics\1\2.jpg C:\tina_and_mona\pics\1\3.jpg C:\tina_and_mona\pics\1\4.jpg

void FlickerImage::updateGL()
{
    //qDebug() << "In UpdateGl Event";
    painter.begin(this);
    painter.setRenderHint(QPainter::Antialiasing);
    painter.drawImage ( QRectF(0,0,800,600), images[image_counter], QRectF(0,0, images[image_counter].width(), images[image_counter].height()));
    //painter.fillRect(QRect(0,0,800,600), QColor(0,0,0,255));
    painter.end();
}

void FlickerImage::loadImages()
{
    busy = true;
    images.clear();

    /*images.append(QImage(QDir::toNativeSeparators(QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"1.jpg")));
    images.append(QImage(QDir::toNativeSeparators(QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"2.jpg")));
    images.append(QImage(QDir::toNativeSeparators(QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"3.jpg")));
    images.append(QImage(QDir::toNativeSeparators(QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"4.jpg")));*/

    images.append(QImage(QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"1.jpg")));
    images.append(QImage(QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"2.jpg")));
    images.append(QImage(QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"3.jpg")));
    images.append(QImage(QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"4.jpg")));

    qDebug() << "Before output file";
    QFile output("image.log");

    if(!output.open(QIODevice::WriteOnly | QIODevice::Text | QIODevice::Append))
    {
        qDebug() << "Could not open output";
    }

    else
    {
        qDebug() << "image.log could be opened";
        output.write(QString("hi").toAscii());
        output.write(QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"1.jpg\n").toAscii());
        output.write((QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"2.jpg\n")).toAscii());
        output.write((QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"3.jpg\n")).toAscii());
        output.write((QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"4.jpg\n")).toAscii());
        output.close();
    }

    busy = false;

}

I have experienced black OpenGL output too. It was fixed by updating the graphics card driver. So I recommend that you try that first. — user362638
Its seems to be related to the plugin system. qApp->addLibraryPath("C:/customPath/plugins"); doc.qt.nokia.com/4.7-snapshot/… Copying the needed wont work. I will copy all and test it ;) — user1439712
Did like this guy recommended: deskew.com/blog/tags/qt-plugins-deploy But all needed plugin folders in the same dir as your app. Did not work too — user1439712
Asked in the qt forums for help too, im realy mad right now... write once, use on every system... my ass developer.nokia.com/Community/Discussion/… — user1439712
Are you absolutely sure, that your program can open those jpgs in the other computer? Try to show them in some QLabel to check that jpgs are found and they work. — user362638

Unknown Unknown · Accepted Answer · 2012-06-20T19:59:42

This probably doesn't fix the problem, but the way the images are added to the list really hurts my eyes ;) Instead of this:

images.append(QImage(QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"1.jpg")));
images.append(QImage(QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"2.jpg")));
images.append(QImage(QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"3.jpg")));
images.append(QImage(QDir::toNativeSeparators(QDir::currentPath() + QDir::separator () + QString("pics") + QDir::separator () + QString::number(counter) + QDir::separator()+"4.jpg")));

Try something like this:

for (int i = 0; i < 4; ++i)
{
    QString imagePath = QString("%1/pics/%2/%3.jpg")
        .arg(qApp->applicationDirPath()).arg(counter).arg(i);
    if (QFileInfo::exists(imagePath))
    {
        QImage image(imagePath);
        if (image.isNull())
            qDebug() << "ERROR, image load failed: " << imagePath;
        else
            images.append(image);
    }
    else
    {
        qDebug() << "ERROR, cannot find file: " << imagePath;
    }
}

Note that you really do not need to convert the file paths to use native separators. You need to do that only if you are showing the path to the user. All operating systems that I know (including Windows) work fine with normal slash /.

You are also using QDir::currentPath(). My guess is that what you really want is the application's directory, which doesn't need to be the same as the current directory. Use qApp->applicationDirPath() instead.

And it usually doesn't hurt to do some error checking.

QT QGL Black Widget on different pc

3 Answers