The main motivation behind this change is to prepare kwin for importing
kwayland-server code in libkwin.
As is, builtin effects are linked with libkwin. Some builtin effects
have wayland specific code. If we move wayland stuff in libkwin, there's
going to be a circular dependency between kwin4_effect_builtins and
libkwin targets.
This change intends to break that dependency by linking builtin effects
to kwin executable.
The main issue with that is that EffectLoader would need to discover the
effects indirectly. QStaticPlugin is used for that purpose.
Besides breaking the cyclic dependency, it makes builtin effects use the
same plugin infrastructure in libkwineffects that external effects use.
Metadata in src/effects/effect_builtins.cpp was converted in a list of
python dictionaries, which was fed to a python script that generated
main.cpp and metadata.json files.
Currently, cpp source files are included partially in effect sub-folders
and src/effects/CMakeLists.txt, which is really confusing and hard to
follow.
With this change, effect targets will be defined in their own subfolders.
This makes build files more straightforward.
Effect sub-targets are eventually merged into a monolithic
kwin4_effect_builtins target.
Another reason for modularizing builtin effects is that no two effects
can generate moc files with the same name atm even though they are in
different sub-folders. This can be potentially useful in the future, e.g.
making effects static plugins in order to decouple builtin effects from
libkwin (every effect subfolder would need a main.cpp or plugin.cpp file,
which will include the associated moc file).
Once in a while, we receive complaints from other fellow KDE developers
about the file organization of kwin. This change addresses some of those
complaints by moving all of source code in a separate directory, src/,
thus making the project structure more traditional. Things such as tests
are kept in their own toplevel directories.
This change may wreak havoc on merge requests that add new files to kwin,
but if a patch modifies an already existing file, git should be smart
enough to figure out that the file has been relocated.
We may potentially split the src/ directory further to make navigating
the source code easier, but hopefully this is good enough already.
