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Move our plugins into .thumbnailer files

What

Now that we have support for .thumbnailer files that reside in /usr/share/thumbnailers, we should start moving our own plugins into such, so that we're following this de-facto standard other desktop environments do.

This de-facto standard was popularized by GNOME with their thumbnailers for Nautilus:

Moving these plugins into similar little binaries allows them to

  • Working nicer with sandboxing
  • Being distributable with flatpaks
  • Easing future transitions (KF6 to KF7 for example)
  • Works with other file explorers

How

It should be relatively simple process: We make a plugin a QApplication, create a .thumbnailer file for it, and then tell CMake to install it to ${KDE_INSTALL_DATADIR}/thumbnailers/

Here's the first plugin that I have been moving, which can serve as an example: !368

We could potentially make a macro to make this easier, but I also feel like making the macro is going to take just as long as going the plugins one by one ;) (well, at least for me)

Plugins to move

  • Appimagecreator
  • Audiocreator
  • Comiccreator
  • Cursorcreator !368
  • Djvucreator
  • Ebookcreator
  • Exrcreator
  • Imagecreator
    • Merge with jpegcreator
    • Merge with svgcreator
  • Kritacreator
  • Opendocumentcreator
  • Textcreator
  • Windowsexecreator
  • Windowsimagecreator

Note about folders

Folder thumbnails are handled by kio-extras thumbnail.cpp

From directorycreator.cpp

    // The actual implementation for directory thumbnails is in thumbnail.cpp
    // This class is only a dummy to produce a KPluginMetaData so that the directory thumbnailer is listed by PreviewJob::availablePlugins()

We can just add a separate toggle for this in the settings and simplify this part, but this is why I'm not moving the directory thumbnailer, since it's just a dummy plugin.

Testing

Currently our plugins override the thumbnailer files, so to properly test this, you have to rebuild kio where in previewjob.cpp you comment out the following part:

            jsonMetaDataPlugins = KPluginMetaData::findPlugins(QStringLiteral("kf6/thumbcreator"));

This makes KIO only look for the standardized thumbnailers and ignore the plugins, so you can test them properly.

Removing the plugins when all is done

This is something I don't know how to do, but we need to somehow get the old plugins out of the systems. Is this distro thing, or something else?

Edited by Akseli Lahtinen