Building a Qt Image Plugin throws "invalid new-expression of abstract class type 'ArgbHandler'" error

Hans

Hi,
i tried to compile a QT Image Plugin. I used the tutorial here. But it is quite old. And I cannot find a new version.

http://doc.qt.digia.com/qq/qq17-imageio.html

Here are the code snippets that belongs to the error message:

class ArgbPlugin : public QImageIOPlugin
{
  QImageIOHandler *create(QIODevice *device, const QByteArray &format = QByteArray()) const;
};

QImageIOHandler *ArgbPlugin::create( QIODevice *device, const QByteArray &format) const
{
    QImageIOHandler *handler = new ArgbHandler;
    handler->setDevice(device);
    handler->setFormat(format);
    return handler;
}

class ArgbHandler : public QImageIOHandler
{
public:
    ArgbHandler();
    ~ArgbHandler();
 
// some methods are following....
};

Maybe someone can give me a hint.

I dont know how to append a file here in the forum. I could also send the whole qt project.

I am using QT 5.4.1 ,QT Creator 3.3.1 on windows 7 64 bit.

[edit: added missing coding tags SGaist]

SGaist

Hi and welcome to devnet,

Did you implement both read and canRead in ArgbHandler ?

Hans

Hi,
thanks for your help. :)

I will put the code to pastbin so it is easier to read.

http://pastebin.com/8hc1Fv5g
http://pastebin.com/DGxztH81
http://pastebin.com/DuRkrkva
http://pastebin.com/bpV8hgkC

http://pastebin.com/jcdQgw4c

I think read and canRead are put in properly.

Hans

Here I also uploaded the whole source.

http://www.file-upload.net/download-10397238/ARGB2.zip.html

SGaist

canRead is not implemented nor called properly

It isn't a static function (which you can't override by the way)

bool ArgbHandler::canRead() const
{
    return device()->peek(4) == "\xCA\xFE\x12\x34";
}

class ArgbHandler : public QImageIOHandler
{
public:
    ArgbHandler();
    ~ArgbHandler();

    bool read(QImage *image);
    bool write(const QImage &image);

    bool canRead() const;

    QVariant option(ImageOption option) const;
    void setOption(ImageOption option, const QVariant &value);
    bool supportsOption(ImageOption option) const;
};

which builds properly, however, I haven't done any run tests. You would also need to correct ArgbPlugin::capabilities for your plugin to build properly

Hans

Hi,
thanks for your quick answer.

I could also compile it. My intension for the plugin was to get support for the OpenEXR file format in qt. I compiled the OpenEXR libs but i have not found a good tutorial how to finally connect them with the compiled plugin so I can load exr files as a QImage.

SGaist

Do you mean get the data from an OpenEXR image in QImage or use the plugin ?

Hans

yes, basically I want to load an OpenEXR image in QImage. The format is not supported. Therefore I wanted to use the plugin.

SGaist

Sorry, I meant, do you have problem getting the plugin to load ? Or do you have problem to read images from an OpenEXR file ?

Hans

The plugin is loading correctly. I created a new simple QT app there i created a QImage.

I add the plugin via: QCoreApplication::addLibraryPath("some_path/plugins");

The app runs without an error.

But my problem is how can read an Open EXR image now. I guess I have to include the Openexr libs and use some special code for exr?

SGaist

Yes, you will need to convert your EXR images in something supported by QImage