Proof of concept importing svg into CadQuery

fish-to-cq.py

#!/usr/bin/python

######################################################################
#  A proof of concept adding a svg path into a cadQuery Workspace
#  object.
#
#  This file is in the public domain.
#
#  Dov Grobgeld <[email protected]>
#  2024-03-10 Sun
######################################################################

import svgpathtools
from svgpathtools import svg2paths
import cadquery as cq
from cadquery import exporters
import numpy as np
from math import sin, cos, sqrt, pi, acos, fmod, degrees
import pdb

def tpl(cplx):
  '''Convert a complex number to a tuple'''
  return (cplx.real,cplx.imag)

def angle_between(u,v):
  '''Find the angle between the vectors u an v'''
  ux,uy = u
  vx,vy = v
  sign = 1 if ux*vy-uy*vx > 0 else -1
  arg = (ux*vx+uy*vy)/(sqrt(ux*ux+uy*uy)*sqrt(vx*vx+vy*vy))
  return sign*acos(arg)

# Implementation of https://www.w3.org/TR/SVG/implnote.html#ArcConversionCenterToEndpoint
def arc_endpoint_to_center(
  start,
  end,
  flag_a,
  flag_s,
  radius,
  phi):
  '''Convert a endpoint elliptical arc description to a center description'''
  rx,ry = radius.real,radius.imag
  x1,y1 = start.real,start.imag
  x2,y2 = end.real,end.imag
  
  cosphi = cos(phi)
  sinphi = sin(phi)
  rx2 = rx*rx
  ry2 = ry*ry

  # Step 1. Compute x1p,y1p
  x1p,y1p = (np.array([[cosphi,sinphi],
                       [-sinphi,cosphi]])
             @ np.array([x1-x2, y1-y2])*0.5).flatten()
  x1p2 = x1p*x1p
  y1p2 = y1p*y1p

  # Step 2: Compute (cx', cy')
  cxyp = sqrt((rx2*ry2 - rx2*y1p2 - ry2*x1p2)
              / (rx2*y1p2 + ry2*x1p2)) * np.array([rx*y1p/ry,-ry*x1p/rx])

  if flag_a == flag_s:
    cxyp = -cxyp

  cxp,cyp = cxyp.flatten()

  # Step 3: compute (cx,cy) from (cx',cy')
  cx,cy = (cosphi*cxp - sinphi * cyp + 0.5*(x1+x2),
           sinphi*cxp + cosphi * cyp + 0.5*(y1+y2))

  # Step 4: compute theta1 and deltatheta
  theta1 = angle_between((1,0), ((x1p-cxp)/rx, (y1p-cyp)/ry))
  delta_theta = fmod(angle_between(((x1p-cxp)/rx,(y1p-cyp)/ry),
                                   ((-x1p-cxp)/rx, (-y1p-cyp)/ry)),2*pi)

  # Choose the right edge according to the flags
  if not flag_s and delta_theta > 0:
    delta_theta -= 2*pi
  elif flag_s and delta_theta < 0:
    delta_theta += 2*pi
    
  return (cx,cy), theta1, delta_theta

def addSvgPath(self, path):
  '''Add the svg path object to the current workspace'''
  res = self
  path_start = None
  arc_id = 0
  for p in path:
    if path_start is None:
        path_start = p.start
    res = res.moveTo(*tpl(p.start))

    # Support the four svgpathtools different objects
    if isinstance(p, svgpathtools.CubicBezier):
      coords = (tpl(p.start), tpl(p.control1), tpl(p.control2), tpl(p.end))
      res = res.bezier(coords)
    elif isinstance(p, svgpathtools.QuadraticBezier):
      coords = (tpl(p.start), tpl(p.control), tpl(p.end))
      res = res.bezier(coords)
      pass
    elif isinstance(p, svgpathtools.Arc):
      arc_id += 1
      center,theta1,delta_theta = arc_endpoint_to_center(
        p.start,
        p.end,
        p.large_arc,
        p.sweep,
        p.radius,
        p.rotation)

      res = res.ellipseArc(
        x_radius = p.radius.real,
        y_radius = p.radius.imag,
        rotation_angle=degrees(p.rotation),
        angle1= degrees(theta1),
        angle2=degrees(theta1+delta_theta)
        )
    elif isinstance(p, svgpathtools.Line):
      res = res.lineTo(p.end.real, p.end.imag)

    if path_start == p.end:
      path_start = None
      res = res.close()

  return res

cq.Workplane.addSvgPath = addSvgPath

paths, attributes = svg2paths('fish.svg')
res = (cq
       .Workplane('XY')
       .addSvgPath(paths[0])
       .extrude(10)
       # Why do I get an error trying to fillet here?
       )
  
exporters.export(res, 'fish.stl')

print('ok')

fish.svg