As proposed by Mitch. This completes first renaming attempt (commit
08ffc10) with even less ambiguous names.
"horizontal-axis-position" and "vertical-axis-position" are now
respectively "mirror-position-y" and "mirror-position-x".
"Horizontal position" and "Vertical position" could be mistaken as
meaning respectively the x and y coordinates, hence the vertical (resp.
horizontal) guide's positions.
The more accurate "horizontal-axis-position" and "vertical-axis-position"
namings are less misleading.
You can now set any paint tool to mirror painting relatively
horizontal/vertical axis or a central point (any combination of these 3
symmetries).
This has been implemented as a new multi-stroke core, where every stroke
is actually handled as a multi-stroke (default of size 1).
This is also the first usage of custom guides for symmetry guiding.
Current version has to be activated in the playground.
