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#!/usr/bin/env python3
# This file is part of Precut.
# Precut 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.
# Precut is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with Precut. If not, see <>.
# please, stick to pep8 formatting for this file
# seems to be lost in year 2016
Migrator: Mario Voigt / FabLab Chemnitz
Date: 13.08.2020
This plugin - initially called "Precut" - was found deeply on web and was nearly lost in translation. Ported to Python 3.0 for InkScape 1.0. This tool finds path intersections within the complete SVG document. Intersections are going to be marked with little squares.
What do we want to check?
* any text objects that are not converted to a path?
* can be implemented as tag blacklist
* any outlines? they need to be converted to paths
* check for crossing paths
* this is the hardest
* for lines, this is easy, and can, for example, be done with shapely:
>>> from shapely.geometry import LineString
>>> l1 = LineString([(0, 0), (1, 1)])
>>> l2 = LineString([(0, 1), (1, 0)])
>>> l1.intersects(l2)
>>> p = l1.intersection(l2)
>>> p.x
>>> p.y
* check for self-intersection, too (=> line.is_simple)
* need to split each complex subpath into its segments
* then, when doing intersections, remove the `boundary`
from the intersection set, because two adjacent
segments from a subpath always intersect in their boundary
* handle the commands M, Z, L, C, Q, A (parsed via simplepath)
* M: moveto
* Z: closepath (straight closing line)
* L: lineto
* C: curveto (cubic bezier)
* Q: curveto (quadratic bezier)
* A: elliptical arc (circles, ellipsis)
* paths need to have a minimum distance to other paths
* if two paths are connected ("T-junction"), this junction needs to be
exempt from the distance check.
from lxml import etree
import inkex
from inkex import bezier
from inkex.paths import Path
from inkex import Color
import sys
import logging
from shapely.geometry import LineString, MultiLineString, Point, MultiPoint, GeometryCollection
from shapely import speedups
if speedups.available:
logger = logging.getLogger(__name__)
def take_N(seq, n):
split ``seq`` into slices of length ``n``. the total
length of ``seq` must be a multiple of ``n``.
if len(seq) % n != 0:
raise ValueError("len=%d, n=%d, (%s)" % (len(seq), n, seq))
sub = []
for elem in seq:
if len(sub) == n:
yield sub
sub = []
def linear_interp(a, b, t):
linearly interpolate between ``a`` and ``b``. ``t`` must be a
a float between 0 and 1.
return (1 - t) * a + t * b
def sample(start, stop, num):
interpolate between start and stop, and yield ``num`` samples
if num == 0:
delta = 1.0 / num
t = 0
for i in range(num):
yield linear_interp(start, stop, t)
t += delta
class CheckerResult(object):
def __init__(self, msg, elem, extra=None, max_len=50):
self.msg = msg
self.elem = elem
self.extra = extra
self.max_len = max_len
def fmt(self, s):
s = ", ".join(["%s: %s" % (k, v) for k, v in s.items()])
if len(s) > self.max_len:
return s[:50] + u""
return s
def __unicode__(self):
msg, elem, extra = self.msg, self.elem, self.extra
if extra:
return "%s: %s (%s)" % (msg, elem.get("id"), self.fmt(extra))
return "%s: %s" % (msg, elem.get("id"))
def __repr__(self):
return "<CheckerResult: %s>" % self.msg
class Checker(object):
def __call__(self, elem):
run a check on ``elem`` and yield (elem, message) tuples
for each failed check
raise NotImplementedError("please implement __call__")
def collect(self):
run a second stage check on aggregated data
return []
class StyleChecker(Checker):
def __call__(self, elem):
style = elem.get("style")
if style is None:
parsed = dict(inkex.Style.parse_str(style))
if "stroke" in parsed and parsed["stroke"] != "none":
yield CheckerResult("element with stroke found", elem)
class ElemBlacklistChecker(Checker):
blacklist = ["text"]
def __call__(self, elem):
_, tag = elem.tag.rsplit("}", 1)
if tag in self.blacklist:
yield CheckerResult("'%s' element found in document" % tag, elem)
class Subpath(object):
def __init__(self):
self.points = []
self.cursor = None
def __len__(self):
return len(self.points)
def last_point(self):
if self.points:
return self.points[-1]
def first_point(self):
if self.points:
return self.points[0]
def moveto(self, point):
assert len(self) == 0, "moveto may only be called at the beginning of a subpath"
self.cursor = point
def lineto(self, point):
self.cursor = point
def curveto(self, points):
for p in self.approx_curve([self.cursor] + points):
def closepath(self):
def add_points(self, points):
self.cursor = points[-1]
def as_linestring(self):
return LineString(self.points)
def approx_curve(self, points):
for four in take_N(points, 4):
# TODO: automatically set number of samples depending on length
for t in sample(0, 1, 50):
yield bezier.bezierpointatt(four, t)
class IntersectionChecker(Checker):
def __init__(self):
self.paths = []
def __call__(self, elem):
# logger.debug(elem.attrib)
path = elem.get("d")
if path is None:
return []
parsed = Path(path).to_arrays()
self.paths.append((parsed, elem))
# logger.debug(parsed)
return []
def fixVHbehaviour(self, elem):
raw = Path(elem.get("d")).to_arrays()
subpaths, prev = [], 0
for i in range(len(raw)): # Breaks compound paths into simple paths
if raw[i][0] == 'M' and i != 0:
prev = i
seg = []
for simpath in subpaths:
if simpath[-1][0] == 'Z':
simpath[-1][0] = 'L'
if simpath[-2][0] == 'L': simpath[-1][1] = simpath[0][1]
else: simpath.pop()
for i in range(len(simpath)):
if simpath[i][0] == 'V': # vertical and horizontal lines only have one point in args, but 2 are required
simpath[i][0]='L' #overwrite V with regular L command
add=simpath[i-1][1][0] #read the X value from previous segment
simpath[i][1].append(simpath[i][1][0]) #add the second (missing) argument by taking argument from previous segment
simpath[i][1][0]=add #replace with recent X after Y was appended
if simpath[i][0] == 'H': # vertical and horizontal lines only have one point in args, but 2 are required
simpath[i][0]='L' #overwrite H with regular L command
simpath[i][1].append(simpath[i-1][1][1]) #add the second (missing) argument by taking argument from previous segment
elem.set("d", Path(seg))
return seg
def get_line_strings(self):
# logger.debug("paths: %s", self.paths)
for path, elem in self.paths:
path = self.fixVHbehaviour(elem)
logger.debug("new path, %s", elem.get("id"))
current_subpath = Subpath()
for cmd, coords in path:
logger.debug(" new command: %s", cmd)
if cmd != "A":
points = list(take_N(coords, n=2))
points = list(take_N(coords, n=7))
logger.debug(" points: %s", points)
if cmd == "M":
# M starts a new subpath
if len(current_subpath) > 1:
yield current_subpath, elem
current_subpath = Subpath()
# more than one point means the rest of the points are to
# be treated as if cmd was L:
if len(points) > 1:
points = points[1:]
cmd = "L"
if cmd == "L":
if cmd == "Z":
if cmd == "C":
if cmd == "Q":
logger.warning("quadratic beziers are not supported yet")
# current_subpath.moveto(points[-1])
if cmd == "A":
logger.warning("elliptic arcs are not supported yet")
if len(current_subpath) > 1:
yield current_subpath, elem
current_subpath = Subpath()
def collect(self):
return self.check_intersections()
def check_intersections(self):
checks_done = MultiLineString()
for subpath, elem in self.get_line_strings():
line = subpath.as_linestring()
if not line.is_simple:
# TODO: find location of self-intersection and introduce some
# tolerance
# checks_done = checks_done.union(line)
yield CheckerResult("self-intersection found", elem)
# continue
if checks_done.intersects(line):
intersection = checks_done.intersection(line)
yield CheckerResult("intersection found", elem, extra={"intersection": intersection})
checks_done = checks_done.union(line)
class ErrorVisualization(object):
def __init__(self, svg, effect, color, group_id="precut_errors"):
self.svg = svg
self.color = color
g = svg.find(".//%s[@id='%s']" % (inkex.addNS("g", "svg"), group_id))
if g is not None:
self.g = g
parent = svg
attrs = {"id": group_id, "style": "opacity:.5", inkex.addNS("label", "inkscape"): "Precut Errors"}
self.g = etree.SubElement(parent, inkex.addNS("g", "svg"), attrs)
def fmt_point(self, point):
return "%s %s" % point
def convert(self, geom):
convert a shapely geometry to SVG
def vis_line_string(geom):
path = []
point_iter = iter(geom.coords)
head = next(point_iter)
tail = list(point_iter)
path.append("M%s" % self.fmt_point(head))
for point in tail:
path.append("L%s" % self.fmt_point(point))
attrs = {"d": " ".join(path), "style": "stroke:%s;stroke-width:5px;" % self.color}
etree.SubElement(self.g, inkex.addNS("path", "svg"), attrs)
def vis_point(geom):
x, y = geom.x, geom.y
x1, y1 = x - 5, y - 5
x2, y2 = x - 5, y + 5
x3, y3 = x + 5, y + 5
x4, y4 = x + 5, y - 5
vis_line_string(LineString([(x1, y1), (x2, y2), (x3, y3), (x4, y4), (x1, y1)]))
def vis_geom_collection(geom):
for g in geom.geoms:
converters = {
LineString: vis_line_string,
Point: vis_point,
MultiLineString: vis_geom_collection,
MultiPoint: vis_geom_collection,
GeometryCollection: vis_geom_collection,
def add_error(self, geom):
class PathIntersections(inkex.Effect):
def __init__(self, *args, **kwargs):
self.check_result = []
self.checkers = [ElemBlacklistChecker(), StyleChecker(), IntersectionChecker()]
inkex.Effect.__init__(self, *args, **kwargs)
self.arg_parser.add_argument("--color", type=Color, default='4012452351', help="Error highlight color")
def walk(self, elem):
if elem.get("id") == "precut_errors":
for child in elem.iterchildren():
def visit(self, elem):
logger.debug("visiting %s", elem)
for checker in self.checkers:
def effect(self):
svg = self.document.getroot()
vis = ErrorVisualization(svg, self, color=self.options.color)
# additional "collect" pass for "global" analysis
for checker in self.checkers:
for res in self.check_result:
#print >>sys.stderr, unicode(res).encode("utf8")
#print(sys.stderr, str(res.encode("utf8")))
if res.extra and "intersection" in res.extra:
# TODO: add visualization for other kinds of errors
if __name__ == "__main__":
logging.basicConfig(stream=sys.stderr, level=logging.WARNING, format="%(levelname)s %(message)s")