inkscape/share/extensions/render_gears.py

#!/usr/bin/env python3
#
# Copyright (C) 2007 Aaron Spike  (aaron @ ekips.org)
# Copyright (C) 2007 Tavmjong Bah (tavmjong @ free.fr)
#
# 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
#
"""
Generate gears 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 Gears(inkex.GenerateExtension):
    container_label = "Rendered Gears"

    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=20.0, 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__":
    Gears().run()