gcc can recognize various regexps in comments. Since C++17 provides
[[fallthrough]], using /* fallthrough */ consistently seems
appropriate until we switch to C++17.
see also https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
* unify line-width calculation
* thin line-width, approximate thickness of
glyph stroke width at same UI scale
* don't use outlines (except main tool buttons)
This fixes issues of generic buttons with bright-theme
* pixel align some lines
A "fall through" comment is most portable way to indicate
"no break, fallthru" cases.
* __attribute__ ((fallthrough)) // is not portable
* [[fallthrough]]; // is C++17
