I created dbusmenu-qt as part of my work for Canonical, so I do not consider it to be a product I "own". This is one of the subtle consequences of contributing code because you are paid to do so, and not because this is something you are genuinely interested in working on.

I agree, unless the XDG spec evolves, it is becoming more and more useless anyway.

Small nitpick on a coding style issue, but the code looks good, thanks for your work!

LGTM, but I agree you could get rid of fitsplugin.h in lib/CMakeLists.txt

Some minor requests, but we are getting there!

I think the basic problem here that the static Qt plugin is put inside a shared library

Why is this restricted to Linux? Does it work out of the box on Windows and macOS?

The fits decoding is moved to imageformats as you requested.
I had huge problems with the static plugin registration, the old way did not work at all. I finally figured out a workaround hack, but I had to spend couple of hours on this. Explanation is written in app/CMakeLists.txt.

Looks good, thanks for simplifying exception handling code in Exiv2ImageLoader.

Regarding kimageformats:

• You don't need to provide write support: some formats are read-only (see README.md)
• Adding fits format to kimageformats also means Dolphin and the file dialogs can show thumbnails for .fits files, maybe that could be useful?
• It is true that you would have to duplicate some code to add metadata support in Gwenview. The right way to avoid that would be to create a Qt library to handle the fits image format and use it in kimageformats and Gwenview (and KStars maybe?). That's more work to do though, so I can understand if you don't want to go that way, but if you are already duplicating code from KStars to Gwenview to add fits support (I haven't checked if it is the case), then creating a library would make sense.

OK, makes sense.

It works for me:

[perso ~/src/colorpick/build]
$ which gcc
/usr/lib/ccache/gcc
[perso ~/src/colorpick/build]
$ cmake -G Ninja ..
-- The C compiler identification is GNU 6.2.0
-- The CXX compiler identification is GNU 6.2.0
-- Check for working C compiler using: Ninja
-- Check for working C compiler using: Ninja -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler using: Ninja
-- Check for working CXX compiler using: Ninja -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/perso/src/colorpick/build
[perso ~/src/colorpick/build]
$ ccache -s
cache directory                     /home/perso/.ccache
primary config                      /home/perso/.ccache/ccache.conf
secondary config      (readonly)    /etc/ccache.conf
cache hit (direct)                   297
cache hit (preprocessed)              15
cache miss                          1390
called for link                     1126
called for preprocessing             167
multiple source files                  1
compile failed                        80
preprocessor error                     7
no input file                         64
files in cache                      1379
cache size                          39.5 MB
max cache size                       1.1 GB
[perso ~/src/colorpick/build]
$ ninja
[1/14] Automatic moc for target colorpick
Generating moc_coloreditor.cpp
Generating moc_colorpicker.cpp
Generating moc_componenteditor.cpp
Generating moc_contrastpreview.cpp
Generating moc_window.cpp
[14/14] Linking CXX executable src/colorpick
[perso ~/src/colorpick/build]
$ ccache -s
cache directory                     /home/perso/.ccache
primary config                      /home/perso/.ccache/ccache.conf
secondary config      (readonly)    /etc/ccache.conf
cache hit (direct)                   297
cache hit (preprocessed)              15
cache miss                          1401
called for link                     1127
called for preprocessing             167
multiple source files                  1
compile failed                        80
preprocessor error                     7
no input file                         64
files in cache                      1412
cache size                          40.0 MB
max cache size                       1.1 GB

Looks good, but I think it would be better if most of the work were in https://cgit.kde.org/kimageformats.git/ instead, unless it is not possible for some reason. Doing it that way would avoid adding a bunch of ifs in Gwenview, but more importantly, would bring support to fits format to all KDE applications. It might still be necessary to add some fits-specific code to show the meta information in Gwenview.

Is this really necessary? Building with ccache is usually just a matter of making sure /usr/lib/ccache comes first in $PATH. Or am I missing something?

Merged in

Looks good!

Ping, do you think this can go in?

Ah, I got stuck with that too! but I solved it in a different way: I merged the direction (left-to-right, right-to-left) and center origin concepts into 3 modes, which can be switched with F2, F3 and F4. You can build the work branch of my scratch repo (git@git.kde.org:clones/kruler/gateau/kruler) to give it a try.

I love the idea, but what about caching? Cached thumbnails are supposed to follow https://specifications.freedesktop.org/thumbnail-spec/thumbnail-spec-latest.html#THUMBSIZE, which still, sadly, says 256.

Looks good!

Ah yes, using keyPressEvent() sounds like a good idea.

Thanks a lot for fixing the mess I created. I just added a note about this to the article on my blog.