QImageIOPlugin doesn't work

sandro4912

I tryed to write a plugin which introduces a new file format .ti which enables reading and writing files in ascii art.

When I try out the plugin in it doesn't seem to work.

My plugin files look like this:

TEMPLATE = lib
TARGET = textimage
CONFIG += plugin release
VERSION = 1.0.0

HEADERS += \
    textimagehandler.h \
    textimageplugin.h

SOURCES += \
    textimagehandler.cpp \
    textimageplugin.cpp

target.path += $$[QT_INSTALL_PLUGINS]/imageformats
INSTALLS += target

DISTFILES += \
    textimageplugin.json

#ifndef TEXTIMAGEHANDLER_H
#define TEXTIMAGEHANDLER_H

#include <QImageIOHandler>

class TextImageHandler : public QImageIOHandler
{
public:
    bool read(QImage *image) override;
    bool write(const QImage &image) override;

    bool canRead() const override;
    static bool canRead(QIODevice *device);
};

#endif // TEXTIMAGEHANDLER_H

#ifndef TEXTIMAGEPLUGIN_H
#define TEXTIMAGEPLUGIN_H

#include <QImageIOPlugin>

class TextImagePlugin : public QImageIOPlugin
{
    Q_OBJECT
    Q_PLUGIN_METADATA(
        IID "org.qt-project.Qt.QImageIOFactoryInterface" FILE "textimageplugin.json")
public:
    QStringList keys() const;

    Capabilities capabilities(
        QIODevice *device, const QByteArray &format) const override;
    QImageIOHandler *create(
        QIODevice *device,
        const QByteArray &format = QByteArray{}) const override;
};

#endif // TEXTIMAGEPLUGIN_H

#include "textimagehandler.h"

#include <QTextStream>
#include <QRegExp>
#include <QImage>

const char map[] =  " .:ilNAM";

bool TextImageHandler::read(QImage *image)
{
    QTextStream stream{device()};
    QString line = stream.readLine();

    if(line !=  "TEXT" || stream.status() != QTextStream::Ok) {
        return false;
    }

    line = stream.readLine();

     QRegExp re( R"(\d+)x(\d+)" );
     int width;
     int height;
     if(re.exactMatch(line)) {

         bool ok;

         width = re.cap(1).toInt(&ok);
         if(!ok) {
             return false;
         }

         height = re.cap(2).toInt(&ok);
         if(!ok) {
             return false;
         }
     }
     else{
         return false;
     }


     QImage result{width, height, QImage::Format_ARGB32};
     for( int y=0; y<height; ++y )
     {
         line = stream.readLine();
         if( line.length() != width )
             return false;

         for( int x=0; x<width; ++x )
         {
             switch( QString(map).indexOf(line[x]) )
             {
             case 0:
                 result.setPixel( x, y, 0xffffffff );
                 break;
             case 1:
                 result.setPixel( x, y, 0xffdfdfdf );
                 break;
             case 2:
                 result.setPixel( x, y, 0xffbfbfbf );
                 break;
             case 3:
                 result.setPixel( x, y, 0xff9f9f9f );
                 break;
             case 4:
                 result.setPixel( x, y, 0xff7f7f7f );
                 break;
             case 5:
                 result.setPixel( x, y, 0xff5f5f5f );
                 break;
             case 6:
                 result.setPixel( x, y, 0xff3f3f3f );
                 break;
             case 7:
                 result.setPixel( x, y, 0xff000000 );
                 break;
             default:
                 return false;
             }
         }
     }

     if(stream.status() != QTextStream::Ok) {
         return false;
     }
     *image  = result;
     return true;
}

bool TextImageHandler::write(const QImage &image)
{
    QTextStream stream{device()};

    stream << "TEXT\n";
    stream << image.width() << "x" << image.height() << "\n";

    for( int y=0; y<image.height(); ++y )
    {
        for( int x=0; x<image.width(); ++x )
        {
            QRgb rgb = image.pixel( x, y );
            int r = rgb & 0xff;
            int g = (rgb >> 8) & 0xff;
            int b = (rgb >> 16) & 0xff;

            stream << map[ 7 - (((r+g+b)/3)>>5) & 0x7 ];
        }
        stream << "\n";
    }

    if( stream.status() != QTextStream::Ok ) {
        return false;
    }
    return true;
}

bool TextImageHandler::canRead() const
{
      return canRead( device() );
}

bool TextImageHandler::canRead(QIODevice *device)
{
    if( device->peek(4) == "TEXT" ) {
        return true;
    }

    return false;
}

#include "textimageplugin.h"

#include "textimagehandler.h"

QStringList TextImagePlugin::keys() const
{
    return QStringList{"ti"};
}

QImageIOPlugin::Capabilities TextImagePlugin::capabilities(
    QIODevice *device, const QByteArray &format) const
{
    if(format == "ti") {
        return (QImageIOPlugin::CanRead | QImageIOPlugin::CanWrite);
    }

    if(!format.isEmpty()) {
        return nullptr;
    }

    if(!device->isOpen()) {
        return  nullptr;
    }

    QImageIOPlugin::Capabilities result;

    if(device->isReadable() && TextImageHandler::canRead(device)) {
        result |= QImageIOPlugin::CanRead;
    }

    if(device->isWritable()) {
        result |= QImageIOPlugin::CanWrite;
    }
    return result;
}

QImageIOHandler *TextImagePlugin::create(
    QIODevice *device, const QByteArray &format) const
{
    auto result = new TextImageHandler{};

    result->setDevice(device);
    result->setFormat(format);
    return result;
}

{
  "Keys": [ "ti" ],
  "MimeTypes": [ "image/ti", "image/ti" ]
}

I generate a plugin file with adding install to make. It looks like this:

Bibliothek "release\textimage1.lib" und Objekt "release\textimage1.exp" werden erstellt.
 copy /y release\textimage1.dll E:\Qt\5.12.2\msvc2017\plugins\imageformats\textimage1.dll
     1 Datei(en) kopiert.
18:55:39: The process "E:\Qt\Tools\QtCreator\bin\jom.exe" exited normally.
18:55:39: Elapsed time: 00:02.

When i try to run a small sample programm the new ti format does not show up:

#include <QApplication>

#include <QImage>
#include <QImageReader>
#include <QByteArray>

#include <QtDebug>

int main( int argc, char **argv )
{ 
    QApplication app( argc, argv );

    for(const auto& supported : QImageReader::supportedImageFormats ()) {
        qDebug() << supported;
    }
}

18:51:03: Starting E:\Cpp_Projekte\QT\Foundations_of_QT\CH11_image_plugin\read\build-read-Desktop_Qt_5_12_2_MSVC2017_32bit-Debug\debug\read.exe ...
"bmp"
"cur"
"gif"
"icns"
"ico"
"jpeg"
"jpg"
"pbm"
"pgm"
"png"
"ppm"
"svg"
"svgz"
"tga"
"tif"
"tiff"
"wbmp"
"webp"
"xbm"
"xpm"
18:51:04: E:/Cpp_Projekte/QT/Foundations_of_QT/CH11_image_plugin/read/build-read-Desktop_Qt_5_12_2_MSVC2017_32bit-Debug/debug/read.exe exited with code 0

What can be wrong. I assumed generating the file under "Qt\5.12.2\msvc2017\plugins\imageformats" is correct?

SGaist

Hi,

Start your application with the QT_DEBUG_PLUGINS environment variable set to 1 to see what happens with your plugin.

Christian Ehrlicher

Apart from @SGaist 's answer - you can't mix debug and release plugins on windows. So either compile your testapp in release mode or your plugin as debug.

sandro4912

I compiled both now as debug and enabled QT_DEBUG_PLUGINS. It gives me this output:

QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/styles/qwindowsvistastyled.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qgifd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qicnsd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qicod.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qjpegd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qsvgd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qtgad.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qtiffd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qwbmpd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qwebpd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/platforms/qwindowsd.dll"

It looks like my dll doesn't even get loaded but why is that so?

The folder contains the file textimage1.dll which is supposed to be the plugin:

0_1561233369247_ba7c8c52-5122-4725-9510-7c56d588b661-image.png

Christian Ehrlicher

There must be also an output during startup - you only pasted the stuff during shutdown...

sandro4912

I get this error on startup:


"The plugin 'E:/Qt/5.12.2/msvc2017/plugins/imageformats/textimage1.dll' uses incompatible Qt library. (Cannot mix debug and release libraries.)" 
         not a plugin
QFactoryLoader::QFactoryLoader() checking directory path "E:/Cpp_Projekte/QT/Foundations_of_QT/CH11_image_plugin/read/build-read-Desktop_Qt_5_12_2_MSVC2017_32bit-Debug/debug/imageformats" ...
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qgifd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qicnsd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qicod.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qjpegd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qsvgd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qtgad.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qtiffd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qwbmpd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qwebpd.dll"

I build the plugin and the project with MSVC2017 32 Bit Debug to get the Debug Output. There should not be a mix?

The output of the plugin file looks like this:

22:57:44: Running steps for project image_plugin...
22:57:44: Configuration unchanged, skipping qmake step.
22:57:44: Starting: "E:\Qt\Tools\QtCreator\bin\jom.exe" install
	E:\Qt\Tools\QtCreator\bin\jom.exe -f Makefile.Release install
	copy /y release\textimage1.dll E:\Qt\5.12.2\msvc2017\plugins\imageformats\textimage1.dll
        1 Datei(en) kopiert.
22:57:44: The process "E:\Qt\Tools\QtCreator\bin\jom.exe" exited normally.
22:57:44: Elapsed time: 00:00.

Christian Ehrlicher

@sandro4912 said in QImageIOPlugin doesn't work:

copy /y release\textimage1.dll E:\Qt\5.12.2\msvc2017\plugins\imageformats\textimage1.dll

This does not look like a debug build.

SGaist

Your plugin is named: textimage1.dll It is missing the d suffix for your debug build.

You can use TARGET = $$qtLibraryTarget(textimage)

sandro4912

Than i wonder why it is not build as debug.

I clearly select debug and then build:

0_1561275497852_958750a2-35c8-4131-bb00-c2b24a1eb0fb-image.png

The build settings for debug:

0_1561275704127_5d06df1a-fa93-4f74-b158-600fdf3aff97-image.png

I already removed the release flag from CONFIG so it should not get forced into release or should it?

TEMPLATE = lib
CONFIG += plugin
TARGET = $$qtLibraryTarget(textimage)
VERSION = 1.0.0

HEADERS += \
    textimagehandler.h \
    textimageplugin.h

SOURCES += \
    textimagehandler.cpp \
    textimageplugin.cpp

target.path += $$[QT_INSTALL_PLUGINS]/imageformats
INSTALLS += target

DISTFILES += \
    textimageplugin.json

What does TARGET = $$qtLibraryTarget(textimage) do? why is it needed?

aha_1980

@sandro4912

Your plugin is named: textimage1.dll It is missing the d suffix for your debug build.

On Windows, the library must be called textimage1d.dll if it is a debug version. The reason was already explained above: On Windows, you cannot mix debug and release objects.

sandro4912

Ok but were do i change the name with the d suffix? In the pro file? Or can i just rename it manually?

Christian Ehrlicher

@sandro4912 said in QImageIOPlugin doesn't work:

Ok but were do i change the name with the d suffix? In the pro file? Or can i just rename it manually?

Simply read @SGaist 's answer: 'You can use TARGET = $$qtLibraryTarget(textimage)'

sandro4912

I added the target but it doesn't seem to add the d suffix to make it debug:

TEMPLATE = lib
CONFIG += plugin
VERSION = 1.0.0

HEADERS += \
    textimagehandler.h \
    textimageplugin.h

SOURCES += \
    textimagehandler.cpp \
    textimageplugin.cpp

TARGET = $$qtLibraryTarget(textimage)
target.path += $$[QT_INSTALL_PLUGINS]/imageformats
INSTALLS += target

DISTFILES += \
    textimageplugin.json

SGaist

Did you re-run qmake after changing the TARGET value ?

sandro4912

Ok i guess i forgot to rerun it. Now i could generate the debug files.

When running my testprogram with debug it stills fails but the message is different

Got keys from plugin meta data ()
QFactoryLoader::QFactoryLoader() checking directory path "E:/Cpp_Projekte/QT/Foundations_of_QT/CH11_image_plugin/read/build-read-Desktop_Qt_5_12_2_MSVC2017_32bit-Debug/debug/imageformats" ...
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qgifd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qicnsd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qicod.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qjpegd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qsvgd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qtgad.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qtiffd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qwbmpd.dll"
loaded library "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qwebpd.dll"
"bmp"
"cur"
"gif"
"icns"
"ico"
"jpeg"
"jpg"
"pbm"
"pgm"
"png"
"ppm"
"svg"
"svgz"
"tga"
"tif"
"tiff"
"wbmp"
"webp"
"xbm"
"xpm"
Failed to load.
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/styles/qwindowsvistastyled.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qgifd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qicnsd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qicod.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qjpegd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qsvgd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qtgad.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qtiffd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qwbmpd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/imageformats/qwebpd.dll" 
QLibraryPrivate::unload succeeded on "E:/Qt/5.12.2/msvc2017/plugins/platforms/qwindowsd.dll"

let me know if you need more information...