This make the use of legacy canvas on GTK3 a default-off
advanced config. Legacy is substantially broken on GTK3
and is of basically no use at all to general users on this
platform.
If the program starts with legacy canvas in the config,
it is forced into a GAL mode, as otherwise it could happen
that the user is stuck and unable to get into pcbnew to change
the setting.
Fixes: lp:1803156
* https://bugs.launchpad.net/kicad/+bug/1803156
This can be used for "advanced" options which are for developers
to use for feature-flags and other configuration. Run time config
has some advantages over preprocessor defines:
* Can be changed without recompilation
* Sensitive to XDG_CONFIG_DIR, so flipping configs is easy
* Better compiler coverage (less conditionally compiled code means
less chance to break a different configuration). Also better
analysis coverage.
* Type safe config params
* Centralised documentation: it's in doxygen, in one place
No advanced config should be required by a general users. If a general
user does use one of these configs, it's probably because:
* There is a bug and one of these configs is a workaround
* A config in here is generally useful and should be moved into the
relevant application config and given UI.
For now, the config is read-only, and is read from the
"kicad_advanced" config file in the normal config dir.
John Beard