hi,

inkscape v1.4

how (with a .py extension) do i apply path effects ?
more specifically - add new offset effect with 2.22mm offset.

plus - how do i change an already existing path effect?

TNX

import inkex
from uuid import uuid4

# Make LPE class
class LpeTemplate(inkex.BaseElement):
    tag_name = 'inkscape:path-effect'

class LpeOffset(inkex.EffectExtension):

    def add_arguments(self, pars):
        pass
    
    def effect(self):
        pass
        
        selection_list = self.svg.selected
        if len(selection_list) < 1:
            inkex.errormsg('Please select at least one object')
            return

        offset_float_list = [10, 20, 30, 60]

        lpe_offset_attributes_dict = {'effect':'offset',
                                 #'id':'path-effect1',
                                 'is_visible':'true',
                                 'lpeversion':'1.3',
                                 'linejoin_type':'miter',
                                 'unit':'mm',
                                 'offset':'1',
                                 'miter_limit':'4',
                                 'attempt_force_join':'false',
                                 'update_on_knot_move':'false'}



        for offset_float in offset_float_list:
            current_lpe_offset = LpeTemplate()


            self.svg.defs.append(current_lpe_offset)

            for key, value in lpe_offset_attributes_dict.items():

                current_lpe_offset.set(key, str(value))
                current_lpe_offset.set('id', str(uuid4()))
                current_lpe_offset.set('offset', str(offset_float))

            for selected in selection_list:

                duplicate_element = selected.duplicate()
                duplicate_element.set('inkscape:path-effect', f'#{current_lpe_offset.get_id()}')
        
if __name__ == '__main__':
    LpeOffset().run()

What is required is a 'kick' to force the Inkscape main program to recalculate the offset LPE when the extension returns.

I found for the offset LPE .duplicate() seems to make this happen. 

It can also be done with a command call to rotate 90cw then 90ccw ( so no net effect ) however that is slower and more complex.

tnx...

i achieved this with simpler syntax:

effect = inkex.elements.PathEffect(effect="offset",
               id="path-effect3",
               is_visible="true",
               lpeversion="1.3",
               linejoin_type="miter",
               unit="mm",
               offset="0.4",
               miter_limit="4",
               attempt_force_join="false",
               update_on_knot_move="true")

            self.svg.defs.add(effect)
            selected.set('inkscape:path-effect', effect.get_id(as_url = 1))