Chapter 17.  Inkex Module As API

Inkex Module

Many Inkscape extensions load an SVG file from Inkscape, add some elements on the drawing, and transmit the modified SVG back to Inkscape. For example, the Hello extension discussed in Chapter 5 adds a message on a drawing.

At some point, someone may ask you the question “Can we run the program without Inkscape? I want to run it as a Python program”. The answer is “Yes, definitely”. This article discusses how to do that.

In Ubuntu, the system extension directory is,

/usr/share/inkscape/extensions

The inkex module files are located in the inkex subdirectory. We can treat the module as an API (Application Programming Interface) or a graphics library.

Load Inkex

As we discussed in Chapter 2, the Inkscape invokes Python complier at this location (see below) to run extension programs. The inkex module depends on the lxml module, which is already installed for this compiler.

/usr/bin/python3

We also need to let the compiler know how to find the system extension directory and user extension directory. This is handled by modifying the system environment variable PYTHONPATH. In Bash terminal, type export command to set the variable.

$export PYTHONPATH=${PYTHONPATH}:/usr/share/inkscape/extensions:\
> /home/george/.config/inkscape/extensions  

$echo $PYTHONPATH
:/usr/share/inkscape/extensions:/home/george/......

$/usr/bin/python3
Python 3.9.7 (default, Sep 10 2021, 14:59:43) 
[GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import inkex
>>> import hello
>>> exit()

$/usr/bin/python3 hello_app.py  # see below for hello_app.py

We can also add the export statement to the .bashrc file under Ubuntu user directory. Or create a short Bash script to setup the PYTHONPATH environment variable and run the Python script.

Python Script

Let’s create a Python script hello_app.py to run the code in the Hello extension discussed in Chapter 5. The Hello extension program uses the ArgParse module to parse the arguments. We create a Param class to simulate ArgParse arguments, and override the parse_arguments method to assign a Param object to self.options variable.

The run method derived from EffectExtension class accepts two optional arguments, args and output (see Chapter 3). The args argument must have two instance variables input_file and output. The input_file can be either a stream or a file name. The output instance variable override the output argument of run method. In the example below, the blank_svg is a string representing a blank SVG file in Inkscape.

The script below will create a test.svg in the same directory of hello_app.py file. The run method will invoke the effect method in Hello class defined in hello.py. Notice We are running the program outside of Inkscape. You do not need Inkscape installed to run this Python program.

# hello_app.py
import os
from hello import Hello


class HelloApp(Hello):
    def parse_arguments(self, args):
        self.options = args
        self.options.ids = []
        self.options.selected_nodes = []


class Param:
    def __init__(self):
        self.name = 'Inkex App'
          ## add other GUI variables here


blank_svg = '''<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!-- Created with Inkscape (http://www.inkscape.org/) -->

<svg
   width="210mm"
   height="297mm"
   viewBox="0 0 210 297"
   version="1.1"
   id="svg5"
   inkscape:version="1.1.1 (1:1.1+202109281954+c3084ef5ed)"
   sodipodi:docname="drawing.svg"
   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
   xmlns="http://www.w3.org/2000/svg"
   xmlns:svg="http://www.w3.org/2000/svg">
  <sodipodi:namedview
     id="namedview7"
     pagecolor="#ffffff"
     bordercolor="#666666"
     borderopacity="1.0"
     inkscape:pageshadow="2"
     inkscape:pageopacity="0.0"
     inkscape:pagecheckerboard="0"
     inkscape:document-units="mm"
     showgrid="false"
     inkscape:zoom="0.64052329"
     inkscape:cx="397.33138"
     inkscape:cy="561.25984"
     inkscape:window-width="2560"
     inkscape:window-height="1480"
     inkscape:window-x="0"
     inkscape:window-y="0"
     inkscape:window-maximized="1"
     inkscape:current-layer="layer1" />
  <defs
     id="defs2" />
  <g
     inkscape:label="Layer 1"
     inkscape:groupmode="layer"
     id="layer1" />
</svg>'''


if __name__ == '__main__':
    h = HelloApp()
    args = Param()
    args.input_file = blank_svg.encode('utf-8') # or file name
    args.output = 'test.svg'
    h.run(args)

Others

We can also create a virtual environment with system Python compiler, and install lxml and other modules in the virtual environment. This is the preferred way to work on this type of project.

$python -m venv venv
$source venv/bin/activate
$pip install lxml    ## and other modules