Question

I’m on Windows7 and using Qt SDK 4.8.
Trying to read a file in with QImage but it just doesn’t seem to load. That is, QImage(filename) or QImage(filename, “PNG”) or QImage.load(filename) always return NULL.

Here’s my code:

void MainWindow::on_actionOpen_triggered()
{
    QString fileName = QFileDialog::getOpenFileName(this,
                                                    tr("Open Image"),
                                                    QDir::homePath(),
                                                    tr("Image Files (*.png *.tga *.bmp)"));

    if (!fileName.isEmpty())
    {
        targetImage = new QImage(fileName, "PNG");
        if(targetImage->isNull())
        {
            QMessageBox::information(this,
                                     tr("PhotoChop"),
                                     tr("Cannot load %1.").arg(fileName));
            return;
        }

        onScreenImage.setBackgroundRole(QPalette::Base);
        onScreenImage.setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
        onScreenImage.setScaledContents(true);
        onScreenImage.setPixmap(QPixmap::fromImage(*targetImage));
    }
}

What am I doing wrong?

Answer 1

it has to do with how QImage loads “plugins” for reading files in. One option is to enable these plugins (for different file formats) and then linking against them.

Though instead I just used Gdiplus::Bitmap (from windows) to load in the file and then, from that, created an HBITMAP which QPixmap can use.