DIY extension not appearing in menu - Beyond the Basics

#1

2020-05-21

I'd like to try my hand at making a simple extension for Inkscape (0.92) but cannot even get it to appear in the menu. I started by copying the Render/Gears extension, renaming the files to render_dial.inx and render_dial.py, and putting them in ~/.config/inkscape/extensions/ (which I have confirmed is my user extensions location). I have only made minimal changes to the files - the inx file (render_dial.inx) looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<inkscape-extension xmlns="http://www.inkscape.org/namespace/inkscape/extension">
    <name>Dial</name>
    <id>org.cwo.inkscape.dial</id>
    <param name="teeth"    type="int"   min="6"    max="360"    gui-text="Number of teeth:">24</param>
    <param name="pitch"    type="float" min="0.0"  max="1000.0" gui-text="Circular pitch (tooth size):">20.0</param>
    <param name="angle"    type="float" min="10.0" max="30.0"   gui-text="Pressure angle (degrees):">20.0</param>
    <param name="centerdiameter"    type="float" min="0.0" max="1000.0"   gui-text="Diameter of center hole (0 for none):">20.0</param>
    <param name="unit" gui-text="Units:" type="optiongroup" appearance="combo">
        <option value="px">px</option>
        <option value="in">in</option>
        <option value="mm">mm</option>
    </param>
    <label>Unit of measurement for both circular pitch and center diameter.</label>
    <effect>
        <object-type>all</object-type>
        <effects-menu>
            <submenu name="Render" />
        </effects-menu>                                 
    </effect>
    <script>
        <command location="inx" interpreter="python">render_dial.py</command>
    </script>
</inkscape-extension>

And the Python file (render_dial.py)

#!/usr/bin/env python

"""
Generate dial scale in SVG
"""

from math import acos, cos, pi, radians, sin, sqrt

import inkex
from inkex import PathElement

def involute_intersect_angle(Rb, R):
    Rb, R = float(Rb), float(R)
    return (sqrt(R ** 2 - Rb ** 2) / Rb) - (acos(Rb / R))

def point_on_circle(radius, angle):
    x = radius * cos(angle)
    y = radius * sin(angle)
    return x, y

def points_to_svgd(p):
    f = p[0]
    p = p[1:]
    svgd = 'M{:.5f},{:.5f}'.format(f[0], f[1])
    for x in p:
        svgd += ' L{:.5f},{:.5f}'.format(x[0], x[1])
    svgd += 'z'
    return svgd

class Dial(inkex.GenerateExtension):
    container_label = 'Rendered Dial'

    def add_arguments(self, pars):
        pars.add_argument("--teeth", type=int, default=24, help="Number of teeth")
        pars.add_argument("--pitch", type=float, default=20.0, help="Circular Pitch")
        pars.add_argument("--angle", type=float, default=20.0, help="Pressure Angle")
        pars.add_argument("--centerdiameter", type=float, default=10.0, help="Diameter of hole")
        pars.add_argument("--unit", default="px", help="unit for pitch and center diameter")

    def generate(self):
        teeth = self.options.teeth
        pitch = self.svg.unittouu(str(self.options.pitch) + self.options.unit)
        angle = self.options.angle  # Angle of tangent to tooth at circular pitch wrt radial line.
        centerdiameter = self.svg.unittouu(str(self.options.centerdiameter) + self.options.unit)

        # print >>sys.stderr, "Teeth: %s\n"        % teeth

        two_pi = 2.0 * pi

        # Pitch (circular pitch): Length of the arc from one tooth to the next)
        # Pitch diameter: Diameter of pitch circle.
        pitch_diameter = float(teeth) * pitch / pi
        pitch_radius = pitch_diameter / 2.0

        # Base Circle
        base_diameter = pitch_diameter * cos(radians(angle))
        base_radius = base_diameter / 2.0

        # Diametrial pitch: Number of teeth per unit length.
        pitch_diametrial = float(teeth) / pitch_diameter

        # Addendum: Radial distance from pitch circle to outside circle.
        addendum = 1.0 / pitch_diametrial

        # Outer Circle
        outer_radius = pitch_radius + addendum
        outer_diameter = outer_radius * 2.0

        # Tooth thickness: Tooth width along pitch circle.
        tooth = (pi * pitch_diameter) / (2.0 * float(teeth))

        # Undercut?
        undercut = (2.0 / (sin(radians(angle)) ** 2))
        needs_undercut = teeth < undercut

        # Clearance: Radial distance between top of tooth on one gear to bottom of gap on another.
        clearance = 0.0

        # Dedendum: Radial distance from pitch circle to root diameter.
        dedendum = addendum + clearance

        # Root diameter: Diameter of bottom of tooth spaces.
        root_radius = pitch_radius - dedendum
        root_diameter = root_radius * 2.0

        half_thick_angle = two_pi / (4.0 * float(teeth))
        pitch_to_base_angle = involute_intersect_angle(base_radius, pitch_radius)
        pitch_to_outer_angle = involute_intersect_angle(base_radius, outer_radius) - pitch_to_base_angle

        centers = [(x * two_pi / float(teeth)) for x in range(teeth)]

        points = []

        for c in centers:

            # Angles
            pitch1 = c - half_thick_angle
            base1 = pitch1 - pitch_to_base_angle
            outer1 = pitch1 + pitch_to_outer_angle

            pitch2 = c + half_thick_angle
            base2 = pitch2 + pitch_to_base_angle
            outer2 = pitch2 - pitch_to_outer_angle

            # Points
            b1 = point_on_circle(base_radius, base1)
            p1 = point_on_circle(pitch_radius, pitch1)
            o1 = point_on_circle(outer_radius, outer1)

            b2 = point_on_circle(base_radius, base2)
            p2 = point_on_circle(pitch_radius, pitch2)
            o2 = point_on_circle(outer_radius, outer2)

            if root_radius > base_radius:
                pitch_to_root_angle = pitch_to_base_angle - involute_intersect_angle(base_radius, root_radius)
                root1 = pitch1 - pitch_to_root_angle
                root2 = pitch2 + pitch_to_root_angle
                r1 = point_on_circle(root_radius, root1)
                r2 = point_on_circle(root_radius, root2)
                p_tmp = [r1, p1, o1, o2, p2, r2]
            else:
                r1 = point_on_circle(root_radius, base1)
                r2 = point_on_circle(root_radius, base2)
                p_tmp = [r1, b1, p1, o1, o2, p2, b2, r2]

            points.extend(p_tmp)

        path = points_to_svgd(points)

        # Create SVG Path for gear
        style = {'stroke': '#000000', 'fill': 'none', 'stroke-width': str(self.svg.unittouu('1px'))}
        gear = PathElement()
        gear.style = style
        gear.path = path
        yield gear

        if centerdiameter > 0.0:
            arc = PathElement.arc((0, 0), centerdiameter / 2)
            arc.style = style
            yield arc


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

It does not appear in the Extensions/Render submenu, or anywhere else, nor do I get any error messages when launcing Inkscape from the console. If I change the submenu name to something else, e.g. "blabla" I do get a new submenu on the Extensions menu, but it is empty. If I purposely make an error in the .inx file I get an appropriate error message when launcing Inkscape from the console. So the extension is being found by Inkscape, but no menu entry is created for it. I have tried:

Changing the name of the extension and its files
Changing the id, e.g. to "org.inkscape.extensions.dial"
Putting the files in /usr/share/inkscape/extensions (where the original files are)
Changing the python class name
Changing the submenu name
Changing `<command location="inx" ... ` to `<command reldir="extensions" ... `
Etc

None of this has led to any change in behaviour other than the appearance of a new submenu when one is specified. The actual menu item never appears. Any ideas?

#2

Lomax @Lomax

2020-05-21

This stripped down version doesn't work either.

render_dial.inx

<?xml version="1.0" encoding="UTF-8"?>
<inkscape-extension xmlns="http://www.inkscape.org/namespace/inkscape/extension">
    <name>Dial</name>
    <id>org.cwo.inkscape.dial</id>
    <label>Lorem ipsum</label>
    <effect>
        <object-type>all</object-type>
        <effects-menu>
            <submenu name="Render" />
        </effects-menu>                                 
    </effect>
    <script>
        <command location="inx" interpreter="python">render_dial.py</command>
    </script>
</inkscape-extension>

render_dial.py

#!/usr/bin/env python

import inkex

class Dial(inkex.GenerateExtension):
    container_label = 'Rendered Dial'

    def generate(self):
        yield True

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

No errors, no menu entry, no nothing.

#3

Lomax @Lomax

2020-05-21

*

Ok, I think I found something... If I change...

    <script>
        <command location="inx" interpreter="python">render_dial.py</command>
    </script>

... to...

    <script>
        <command reldir="extensions" interpreter="python">render_dial.py</command>
    </script>

... then the menu item appears. Is location="inx" perhaps a new 1.0 attribute?

#4

Tyler Durden @TylerDurden⚖

2020-05-22

Maybe answer is in in the wiki:

https://wiki.inkscape.org/wiki/index.php?title=Updating_your_Extension_for_1.0

#5

Lomax @Lomax

2020-05-22

Maybe I didn't think to look at that particular page.