Inkscape

For a curator, the external link (to inkscapeforum) is dead.

Hello,
Thank you for providing this extension for Inkscape users!

This is just to let you know that most 3rd party Inkscape extensions, like this one, probably will not work with the upcoming new Inkscape version, the long-awaited version 1.0.

Here is the info you need to update this extension, so that it will work with 1.0 and future versions.
https://wiki.inkscape.org/wiki/index.php?title=Updating_your_Extension_for_1.0

If you have further questions, you can contact Inkscape developers via mailing lists (https://lists.inkscape.org/postorius/lists/?all-lists), forum (https://inkscape.org/forums/extensions/), or the chatroom (https://chat.inkscape.org/channel/team_devel)

If you already have updated it, please disregard this message.

All best,
brynn

How to use it though ?

I've updated the description, hope that helps...

for inkscape 1.0 i made it working by

#!/usr/bin/env python
"""
Derived from the "envelope" extension by Aaron Spike, aaron@ekips.org
By Apex 2011
New version Jens Kober 2017, 2020

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

"""
import inkex
from inkex.localization import inkex_gettext as _

class Mirror(inkex.Effect):
def __init__(self):
inkex.Effect.__init__(self)

def effect(self):
if len(self.options.ids) < 2:
raise inkex.AbortExtension(_("This extension requires two selected objects. \nThe second must be a path, exactly two nodes long."))

#trafo is selected second
obj = self.svg.selected[self.options.ids[0]]
trafo = self.svg.selected[self.options.ids[1]]

if isinstance(trafo, inkex.PathElement):
#distil trafo into two node points
trafoPath = trafo.path.transform(trafo.composed_transform()).to_superpath()
if len(trafoPath[0]) != 2:
raise inkex.AbortExtension(_("The second selected object must be exactly two nodes long."))

# origin of mirror line
ox = trafoPath[0][0][1][0]
oy = trafoPath[0][0][1][1]
# vector along mirror line
vx = trafoPath[0][1][1][0] - ox
vy = trafoPath[0][1][1][1] - oy

# the transformation first translates the origin of the mirror line to [0 0], then rotates the mirror line onto the x-axis,
# reflects everything over the x-axis, undoes the rotation, and finally undoes the translation

# alpha = atan2(vy, vx);

# [1 0 ox] [cos(alpha) -sin(alpha) 0] [1 0 0] [cos(-alpha) -sin(-alpha) 0] [1 0 -ox]
# Transformation = [0 1 oy]*[sin(alpha) cos(alpha) 0]*[0 -1 0]*[sin(-alpha) cos(-alpha) 0]*[0 1 -oy]
# [0 0 1] [ 0 0 1] [0 0 1] [ 0 0 1] [0 0 1]

# after some simplifications (or using your favorite symbolic math software):

# [(vx^2-vy^2)/(vx^2+vy^2) (2 vx vy)/(vx^2+vy^2) (2 vy (ox vy-oy vx))/(vx^2+vy^2)]
# Transformation = [ (2 vx vy)/(vx^2+vy^2) -(vx^2-vy^2)/(vx^2+vy^2) -(2 vx (ox vy-oy vx))/(vx^2+vy^2)]
# [ 0 0 1]

denom = vx**2 + vy**2
a00 = (vx**2 - vy**2) / denom
a01 = (2 * vx * vy) / denom
a02 = 2 * (ox * vy - oy * vx) / denom
mat=[[a00, a01, vy * a02], [a01, -a00, -vx * a02]]
obj.transform = inkex.Transform(mat) * obj.transform

else:
if isinstance(trafo, inkex.Group):
raise inkex.AbortExtension(_("The second selected object is a group, not a path.\nTry using the procedure Object->Ungroup."))
else:
raise inkex.AbortExtension(_("The second selected object is not a path.\nTry using the procedure Path->Object to Path."))

if __name__ == '__main__':
Mirror().run()

@Mario Voigt : Thanks! What I had uploaded indeed only works with the development version of the extensions (but I was told that this is the correct way of getting the selected elements from now onwards). A variant that should work with "plain" 1.0 (based on your code above) is now included in the ZIP.

Updated for v1.2, thanks to Aurèle Duda for the hint!