Flattening SVG groups and handling transforms (#55)

* Some progress (and added CONTRIBUTING.md)

* fixed documentation line-width to be PEP 8 compliant

* fixed documentation line-width to be PEP 8 compliant

* style changes

* made some design changes

* Make the Document class available when importing the library

* Add a method to parse transform strings

* Iterate on the implementation of the Document class

* Tweaks to transform parsing implementation

* Implementing a depth-first flattening of groups

* Finish implementation of flatten_paths

* Beginning to write tests for groups

* Refactoring flatten_paths() into flatten_all_paths()

* Clean up implementation of document classes

* Debugging xml namespace behavior -- needs improvement

* Improve the way the svg namespace is handled

* Print out some paths to see that they're sane

* Fix multiplication of numpy matrices -- need to use .dot() instead of operator*

* Create a unit test for parsing SVG groups

* Return a reference to an element instead of a copied dictionary of attributes

* Add a test for <path> elements that contain a 'transform' attribute

* minor docstring improvements

* got rid of svg2path changes (reverted to master)

* updated to match master

* Remove accidental paranthesis

* Remove unnecessary import

* Use a default width and height of 0, as dictated by SVG specs, in case width or height is missing

* Expose the CONVERSIONS and CONVERT_ONLY_PATHS constants

* Fix the use of some numpy operations

* Remove untested functions

* Fix add_group() and write tests for adding groups and paths

* Update documentation of document module

* Add tests for parsing transforms

* Update the module name for svg_to_paths

* Improve Python3 compatibility

* Try to improve compatibility

* More tweaks for compatibility

.travis.yml

@@ -3,6 +3,6 @@ python:
   - "2.7"
   - "3.6"
 install:
-  - pip install numpy svgwrite
+  - pip install numpy svgwrite future
 script:
   - python -m unittest discover test

setup.py

@@ -31,10 +31,10 @@ setup(name='svgpathtools',
       # download_url = 'http://github.com/mathandy/svgpathtools/tarball/'+VERSION,
       license='MIT',
       
-      install_requires=['numpy', 'svgwrite'],
+      install_requires=['numpy', 'svgwrite', 'future'],
       platforms="OS Independent",
       # test_suite='tests',
-      requires=['numpy', 'svgwrite'],
+      requires=['numpy', 'svgwrite', 'future'],
       keywords=['svg', 'svg path', 'svg.path', 'bezier', 'parse svg path', 'display svg'],
       classifiers = [
             "Development Status :: 4 - Beta",

svgpathtools/__init__.py

@@ -12,6 +12,7 @@ from .paths2svg import disvg, wsvg
 from .polytools import polyroots, polyroots01, rational_limit, real, imag
 from .misctools import hex2rgb, rgb2hex
 from .smoothing import smoothed_path, smoothed_joint, is_differentiable, kinks
+from .document import Document, CONVERSIONS, CONVERT_ONLY_PATHS, SVG_GROUP_TAG, SVG_NAMESPACE
 
 try:
     from .svg_to_paths import svg2paths, svg2paths2

svgpathtools/document.py

@@ -0,0 +1,327 @@
+"""(Experimental) replacement for import/export functionality.
+
+This module contains the `Document` class, a container for a DOM-style 
+document (e.g. svg, html, xml, etc.) designed to replace and improve 
+upon the IO functionality of svgpathtools (i.e. the svg2paths and 
+disvg/wsvg functions). 
+
+An Historic Note:
+     The functionality in this module is meant to replace and improve 
+     upon the IO functionality previously provided by the the 
+     `svg2paths` and `disvg`/`wsvg` functions. 
+
+Example:
+    Typical usage looks something like the following.
+
+        >> from svgpathtools import *
+        >> doc = Document('my_file.html')
+        >> results = doc.flatten_all_paths()
+        >> for result in results:
+        >>     path = result.path
+        >>     # Do something with the transformed Path object.
+        >>     element = result.element
+        >>     # Inspect the raw SVG element. This gives access to the path's attributes
+        >>     transform = result.transform
+        >>     # Use the transform that was applied to the path.
+        >> foo(doc.tree)  # do stuff using ElementTree's functionality
+        >> doc.display()  # display doc in OS's default application
+        >> doc.save('my_new_file.html')
+
+A Big Problem:  
+    Derivatives and other functions may be messed up by 
+    transforms unless transforms are flattened (and not included in 
+    css)
+"""
+
+# External dependencies
+from __future__ import division, absolute_import, print_function
+import os
+import collections
+import xml.etree.ElementTree as etree
+from xml.etree.ElementTree import Element, SubElement, register_namespace, _namespace_map
+import warnings
+
+# Internal dependencies
+from .parser import parse_path
+from .parser import parse_transform
+from .svg_to_paths import (path2pathd, ellipse2pathd, line2pathd, polyline2pathd,
+                        polygon2pathd, rect2pathd)
+from .misctools import open_in_browser
+from .path import *
+
+# To maintain forward/backward compatibility
+from past.builtins import basestring
+from future.utils import iteritems
+
+# Let xml.etree.ElementTree know about the SVG namespace
+SVG_NAMESPACE = {'svg': 'http://www.w3.org/2000/svg'}
+register_namespace('svg', 'http://www.w3.org/2000/svg')
+
+# THESE MUST BE WRAPPED TO OUTPUT ElementTree.element objects
+CONVERSIONS = {'path': path2pathd,
+               'circle': ellipse2pathd,
+               'ellipse': ellipse2pathd,
+               'line': line2pathd,
+               'polyline': polyline2pathd,
+               'polygon': polygon2pathd,
+               'rect': rect2pathd}
+
+CONVERT_ONLY_PATHS = {'path': path2pathd}
+
+SVG_GROUP_TAG = 'svg:g'
+
+
+def flatten_all_paths(
+        group,
+        group_filter=lambda x: True,
+        path_filter=lambda x: True,
+        path_conversions=CONVERSIONS,
+        group_search_xpath=SVG_GROUP_TAG):
+    """Returns the paths inside a group (recursively), expressing the paths in the base coordinates.
+
+    Note that if the group being passed in is nested inside some parent group(s), we cannot take the parent group(s)
+    into account, because xml.etree.Element has no pointer to its parent. You should use Document.flatten_group(group)
+    to flatten a specific nested group into the root coordinates.
+
+    Args:
+        group is an Element
+        path_conversions (dict): A dictionary to convert from an SVG element to a path data string. Any element tags
+                                 that are not included in this dictionary will be ignored (including the `path` tag).
+                                 To only convert explicit path elements, pass in path_conversions=CONVERT_ONLY_PATHS.
+    """
+    if not isinstance(group, Element):
+        raise TypeError('Must provide an xml.etree.Element object. Instead you provided {0}'.format(type(group)))
+
+    # Stop right away if the group_selector rejects this group
+    if not group_filter(group):
+        return []
+
+    # To handle the transforms efficiently, we'll traverse the tree of groups depth-first using a stack of tuples.
+    # The first entry in the tuple is a group element and the second entry is its transform. As we pop each entry in
+    # the stack, we will add all its child group elements to the stack.
+    StackElement = collections.namedtuple('StackElement', ['group', 'transform'])
+
+    def new_stack_element(element, last_tf):
+        return StackElement(element, last_tf.dot(parse_transform(element.get('transform'))))
+
+    def get_relevant_children(parent, last_tf):
+        children = []
+        for elem in filter(group_filter, parent.iterfind(group_search_xpath, SVG_NAMESPACE)):
+            children.append(new_stack_element(elem, last_tf))
+        return children
+
+    stack = [new_stack_element(group, np.identity(3))]
+
+    FlattenedPath = collections.namedtuple('FlattenedPath', ['path', 'element', 'transform'])
+    paths = []
+
+    while stack:
+        top = stack.pop()
+
+        # For each element type that we know how to convert into path data, parse the element after confirming that
+        # the path_filter accepts it.
+        for key, converter in iteritems(path_conversions):
+            for path_elem in filter(path_filter, top.group.iterfind('svg:'+key, SVG_NAMESPACE)):
+                path_tf = top.transform.dot(parse_transform(path_elem.get('transform')))
+                path = transform(parse_path(converter(path_elem)), path_tf)
+                paths.append(FlattenedPath(path, path_elem, path_tf))
+
+        stack.extend(get_relevant_children(top.group, top.transform))
+
+    return paths
+
+
+def flatten_group(
+        group_to_flatten,
+        root,
+        recursive=True,
+        group_filter=lambda x: True,
+        path_filter=lambda x: True,
+        path_conversions=CONVERSIONS,
+        group_search_xpath=SVG_GROUP_TAG):
+    """Flatten all the paths in a specific group.
+
+    The paths will be flattened into the 'root' frame. Note that root needs to be
+    an ancestor of the group that is being flattened. Otherwise, no paths will be returned."""
+
+    if not any(group_to_flatten is descendant for descendant in root.iter()):
+        warnings.warn('The requested group_to_flatten is not a descendant of root')
+        # We will shortcut here, because it is impossible for any paths to be returned anyhow.
+        return []
+
+    # We create a set of the unique IDs of each element that we wish to flatten, if those elements are groups.
+    # Any groups outside of this set will be skipped while we flatten the paths.
+    desired_groups = set()
+    if recursive:
+        for group in group_to_flatten.iter():
+            desired_groups.add(id(group))
+    else:
+        desired_groups.add(id(group_to_flatten))
+
+    def desired_group_filter(x):
+        return (id(x) in desired_groups) and group_filter(x)
+
+    return flatten_all_paths(root, desired_group_filter, path_filter, path_conversions, group_search_xpath)
+
+
+class Document:
+    def __init__(self, filename):
+        """A container for a DOM-style SVG document.
+
+        The `Document` class provides a simple interface to modify and analyze 
+        the path elements in a DOM-style document.  The DOM-style document is 
+        parsed into an ElementTree object (stored in the `tree` attribute).
+
+        This class provides functions for extracting SVG data into Path objects.
+        The Path output objects will be transformed based on their parent groups.
+        
+        Args:
+            filename (str): The filename of the DOM-style object.
+        """
+
+        # remember location of original svg file
+        if filename is not None and os.path.dirname(filename) == '':
+            self.original_filename = os.path.join(os.getcwd(), filename)
+        else:
+            self.original_filename = filename
+
+        if filename is not None:
+            # parse svg to ElementTree object
+            self.tree = etree.parse(filename)
+        else:
+            self.tree = etree.ElementTree(Element('svg'))
+
+        self.root = self.tree.getroot()
+
+    def flatten_all_paths(self,
+                          group_filter=lambda x: True,
+                          path_filter=lambda x: True,
+                          path_conversions=CONVERSIONS):
+        """Forward the tree of this document into the more general flatten_all_paths function and return the result."""
+        return flatten_all_paths(self.tree.getroot(), group_filter, path_filter, path_conversions)
+
+    def flatten_group(self,
+                      group,
+                      recursive=True,
+                      group_filter=lambda x: True,
+                      path_filter=lambda x: True,
+                      path_conversions=CONVERSIONS):
+        if all(isinstance(s, basestring) for s in group):
+            # If we're given a list of strings, assume it represents a nested sequence
+            group = self.get_or_add_group(group)
+        elif not isinstance(group, Element):
+            raise TypeError('Must provide a list of strings that represent a nested group name, '
+                            'or provide an xml.etree.Element object. Instead you provided {0}'.format(group))
+
+        return flatten_group(group, self.tree.getroot(), recursive, group_filter, path_filter, path_conversions)
+
+    def add_path(self, path, attribs=None, group=None):
+        """Add a new path to the SVG."""
+
+        # If we are not given a parent, assume that the path does not have a group
+        if group is None:
+            group = self.tree.getroot()
+
+        # If we are given a list of strings (one or more), assume it represents a sequence of nested group names
+        elif all(isinstance(elem, basestring) for elem in group):
+            group = self.get_or_add_group(group)
+
+        elif not isinstance(group, Element):
+            raise TypeError('Must provide a list of strings or an xml.etree.Element object. '
+                            'Instead you provided {0}'.format(group))
+
+        else:
+            # Make sure that the group belongs to this Document object
+            if not self.contains_group(group):
+                warnings.warn('The requested group does not belong to this Document')
+
+        # TODO: It might be better to use duck-typing here with a try-except
+        if isinstance(path, Path):
+            path_svg = path.d()
+        elif is_path_segment(path):
+            path_svg = Path(path).d()
+        elif isinstance(path, basestring):
+            # Assume this is a valid d-string. TODO: Should we sanity check the input string?
+            path_svg = path
+        else:
+            raise TypeError('Must provide a Path, a path segment type, or a valid SVG path d-string. '
+                            'Instead you provided {0}'.format(path))
+
+        if attribs is None:
+            attribs = {}
+        else:
+            attribs = attribs.copy()
+
+        attribs['d'] = path_svg
+
+        return SubElement(group, 'path', attribs)
+
+    def contains_group(self, group):
+        return any(group is owned for owned in self.tree.iter())
+
+    def get_or_add_group(self, nested_names, name_attr='id'):
+        """Get a group from the tree, or add a new one with the given name structure.
+
+        *nested_names* is a list of strings which represent group names. Each group name will be nested inside of the
+        previous group name.
+
+        *name_attr* is the group attribute that is being used to represent the group's name. Default is 'id', but some
+        SVGs may contain custom name labels, like 'inkscape:label'.
+
+        Returns the requested group. If the requested group did not exist, this function will create it, as well as all
+        parent groups that it requires. All created groups will be left with blank attributes.
+
+        """
+        group = self.tree.getroot()
+        # Drill down through the names until we find the desired group
+        while len(nested_names):
+            prev_group = group
+            next_name = nested_names.pop(0)
+            for elem in group.iterfind(SVG_GROUP_TAG, SVG_NAMESPACE):
+                if elem.get(name_attr) == next_name:
+                    group = elem
+                    break
+
+            if prev_group is group:
+                # The group we're looking for does not exist, so let's create the group structure
+                nested_names.insert(0, next_name)
+
+                while nested_names:
+                    next_name = nested_names.pop(0)
+                    group = self.add_group({'id': next_name}, group)
+                # Now nested_names will be empty, so the topmost while-loop will end
+
+        return group
+
+    def add_group(self, group_attribs=None, parent=None):
+        """Add an empty group element to the SVG."""
+        if parent is None:
+            parent = self.tree.getroot()
+        elif not self.contains_group(parent):
+            warnings.warn('The requested group {0} does not belong to this Document'.format(parent))
+
+        if group_attribs is None:
+            group_attribs = {}
+        else:
+            group_attribs = group_attribs.copy()
+
+        return SubElement(parent, '{{{0}}}g'.format(SVG_NAMESPACE['svg']), group_attribs)
+
+    def save(self, filename=None):
+        if filename is None:
+            filename = self.original_filename
+
+        with open(filename, 'w') as output_svg:
+            output_svg.write(etree.tostring(self.tree.getroot()))
+
+    def display(self, filename=None):
+        """Displays/opens the doc using the OS's default application."""
+
+        if filename is None:
+            filename = self.original_filename
+
+        # write to a (by default temporary) file
+        with open(filename, 'w') as output_svg:
+            output_svg.write(etree.tostring(self.tree.getroot()))
+
+        open_in_browser(filename)

svgpathtools/parser.py

@@ -1,15 +1,18 @@
 """This submodule contains the path_parse() function used to convert SVG path
 element d-strings into svgpathtools Path objects.
-Note: This file was taken (nearly) as is from the svg.path module
+Note: This file was taken (nearly) as is from the svg.path module (v 2.0)."""
-(v 2.0)."""
 
 # External dependencies
 from __future__ import division, absolute_import, print_function
 import re
+import numpy as np
+import warnings
 
 # Internal dependencies
 from .path import Path, Line, QuadraticBezier, CubicBezier, Arc
 
+# To maintain forward/backward compatibility
+from past.builtins import basestring
 
 COMMANDS = set('MmZzLlHhVvCcSsQqTtAa')
 UPPERCASE = set('MZLHVCSQTA')
@@ -26,7 +29,7 @@ def _tokenize_path(pathdef):
             yield token
 
 
-def parse_path(pathdef, current_pos=0j):
+def parse_path(pathdef, current_pos=0j, tree_element=None):
     # In the SVG specs, initial movetos are absolute, even if
     # specified as 'm'. This is the default behavior here as well.
     # But if you pass in a current_pos variable, the initial moveto
@@ -35,7 +38,11 @@ def parse_path(pathdef, current_pos=0j):
     # Reverse for easy use of .pop()
     elements.reverse()
 
+    if tree_element is None:
         segments = Path()
+    else:
+        segments = Path(tree_element=tree_element)
+
     start_pos = None
     command = None
 
@@ -193,3 +200,98 @@ def parse_path(pathdef, current_pos=0j):
             current_pos = end
 
     return segments
+
+
+def _check_num_parsed_values(values, allowed):
+    if not any(num == len(values) for num in allowed):
+        if len(allowed) > 1:
+            warnings.warn('Expected one of the following number of values {0}, but found {1} values instead: {2}'
+                          .format(allowed, len(values), values))
+        elif allowed[0] != 1:
+            warnings.warn('Expected {0} values, found {1}: {2}'.format(allowed[0], len(values), values))
+        else:
+            warnings.warn('Expected 1 value, found {0}: {1}'.format(len(values), values))
+        return False
+    return True
+
+
+def _parse_transform_substr(transform_substr):
+
+    type_str, value_str = transform_substr.split('(')
+    value_str = value_str.replace(',', ' ')
+    values = list(map(float, filter(None, value_str.split(' '))))
+
+    transform = np.identity(3)
+    if 'matrix' in type_str:
+        if not _check_num_parsed_values(values, [6]):
+            return transform
+
+        transform[0:2, 0:3] = np.matrix([values[0:6:2], values[1:6:2]])
+
+    elif 'translate' in transform_substr:
+        if not _check_num_parsed_values(values, [1, 2]):
+            return transform
+
+        transform[0, 2] = values[0]
+        if len(values) > 1:
+            transform[1, 2] = values[1]
+
+    elif 'scale' in transform_substr:
+        if not _check_num_parsed_values(values, [1, 2]):
+            return transform
+
+        x_scale = values[0]
+        y_scale = values[1] if (len(values) > 1) else x_scale
+        transform[0, 0] = x_scale
+        transform[1, 1] = y_scale
+
+    elif 'rotate' in transform_substr:
+        if not _check_num_parsed_values(values, [1, 3]):
+            return transform
+
+        angle = values[0] * np.pi / 180.0
+        if len(values) == 3:
+            offset = values[1:3]
+        else:
+            offset = (0, 0)
+        tf_offset = np.identity(3)
+        tf_offset[0:2, 2:3] = np.matrix([[offset[0]], [offset[1]]])
+        tf_rotate = np.identity(3)
+        tf_rotate[0:2, 0:2] = np.matrix([[np.cos(angle), -np.sin(angle)], [np.sin(angle), np.cos(angle)]])
+        tf_offset_neg = np.identity(3)
+        tf_offset_neg[0:2, 2:3] = np.matrix([[-offset[0]], [-offset[1]]])
+
+        transform = tf_offset.dot(tf_rotate).dot(tf_offset_neg)
+
+    elif 'skewX' in transform_substr:
+        if not _check_num_parsed_values(values, [1]):
+            return transform
+
+        transform[0, 1] = np.tan(values[0] * np.pi / 180.0)
+
+    elif 'skewY' in transform_substr:
+        if not _check_num_parsed_values(values, [1]):
+            return transform
+
+        transform[1, 0] = np.tan(values[0] * np.pi / 180.0)
+    else:
+        # Return an identity matrix if the type of transform is unknown, and warn the user
+        warnings.warn('Unknown SVG transform type: {0}'.format(type_str))
+
+    return transform
+
+
+def parse_transform(transform_str):
+    """Converts a valid SVG transformation string into a 3x3 matrix.
+    If the string is empty or null, this returns a 3x3 identity matrix"""
+    if not transform_str:
+        return np.identity(3)
+    elif not isinstance(transform_str, basestring):
+        raise TypeError('Must provide a string to parse')
+
+    total_transform = np.identity(3)
+    transform_substrs = transform_str.split(')')[:-1]  # Skip the last element, because it should be empty
+    for substr in transform_substrs:
+        total_transform = total_transform.dot(_parse_transform_substr(substr))
+
+    return total_transform

svgpathtools/path.py

@@ -255,6 +255,32 @@ def scale(curve, sx, sy=None, origin=0j):
                         "QuadraticBezier, CubicBezier, or Arc object.")
 
 
+def transform(curve, tf):
+    """Transforms the curve by the homogeneous transformation matrix tf"""
+    def to_point(p):
+        return np.matrix([[p.real], [p.imag], [1.0]])
+
+    def to_vector(z):
+        return np.matrix([[z.real], [z.imag], [0.0]])
+
+    def to_complex(v):
+        return v.item(0) + 1j * v.item(1)
+
+    if isinstance(curve, Path):
+        return Path(*[transform(segment, tf) for segment in curve])
+    elif is_bezier_segment(curve):
+        return bpoints2bezier([to_complex(tf.dot(to_point(p))) for p in curve.bpoints()])
+    elif isinstance(curve, Arc):
+        new_start = to_complex(tf.dot(to_point(curve.start)))
+        new_end = to_complex(tf.dot(to_point(curve.end)))
+        new_radius = to_complex(tf.dot(to_vector(curve.radius)))
+        return Arc(new_start, radius=new_radius, rotation=curve.rotation,
+                   large_arc=curve.large_arc, sweep=curve.sweep, end=new_end)
+    else:
+        raise TypeError("Input `curve` should be a Path, Line, "
+                        "QuadraticBezier, CubicBezier, or Arc object.")
+
+
 def bezier_unit_tangent(seg, t):
     """Returns the unit tangent of the segment at t.
 
@@ -1783,6 +1809,9 @@ class Path(MutableSequence):
             self._start = None
             self._end = None
 
+        if 'tree_element' in kw:
+            self._tree_element = kw['tree_element']
+
     def __getitem__(self, index):
         return self._segments[index]
 

svgpathtools/svg_to_paths.py

@@ -17,6 +17,8 @@ COORD_PAIR_TMPLT = re.compile(
     r'([\+-]?\d*[\.\d]\d*[eE][\+-]?\d+|[\+-]?\d*[\.\d]\d*)'
 )
 
+def path2pathd(path):
+    return path.get('d', '')
 
 def ellipse2pathd(ellipse):
     """converts the parameters from an ellipse or a circle to a string for a 
@@ -79,7 +81,7 @@ def rect2pathd(rect):
     The rectangle will start at the (x,y) coordinate specified by the 
     rectangle object and proceed counter-clockwise."""
     x0, y0 = float(rect.get('x', 0)), float(rect.get('y', 0))
-    w, h = float(rect["width"]), float(rect["height"])
+    w, h = float(rect.get('width', 0)), float(rect.get('height', 0))
     x1, y1 = x0 + w, y0
     x2, y2 = x0 + w, y0 + h
     x3, y3 = x0, y0 + h
@@ -88,6 +90,8 @@ def rect2pathd(rect):
          "".format(x0, y0, x1, y1, x2, y2, x3, y3))
     return d
 
+def line2pathd(l):
+    return 'M' + l['x1'] + ' ' + l['y1'] + 'L' + l['x2'] + ' ' + l['y2']
 
 def svg2paths(svg_file_location,
               return_svg_attributes=False,

test/groups.svg

@@ -0,0 +1,161 @@
+<?xml version="1.0" ?>
+<svg
+    baseProfile="full"
+    version="1.1"
+    viewBox="0 0 365 365"
+    height="100%"
+    width="100%"
+    xmlns="http://www.w3.org/2000/svg"
+    xmlns:test="some://testuri">
+  <defs/>
+  <g
+      id="matrix group"
+      transform="matrix(1.5 0.0 0.0 0.5 -40.0 20.0)">
+
+    <path
+        d="M 183,183 l 0,-50"
+        fill="black"
+        stroke="black"
+        stroke-width="3"
+        test:name="path00"/>
+
+    <g
+        id="scale group"
+        transform="scale(1.25)">
+
+      <path
+            d="M 122,320 l -50,0"
+            fill="black"
+            stroke="black"
+            stroke-width="3"
+            test:name="path01"/>
+
+      <g
+          id="nested group - empty transform"
+          transform="">
+
+        <path
+            d="M 150,200 l -50,25"
+            fill="black"
+            stroke="black"
+            stroke-width="3"
+            test:name="path02"/>
+
+      </g>
+
+      <g
+          id="nested group - no transform">
+
+        <path
+            d="M 150,200 l -50,25"
+            fill="black"
+            stroke="black"
+            stroke-width="3"
+            test:name="path03"/>
+
+      </g>
+
+      <g
+          id="nested group - translate"
+          transform="translate(20)">
+
+        <path
+            d="M 150,200 l -50,25"
+            fill="black"
+            stroke="black"
+            stroke-width="3"
+            test:name="path04"/>
+
+      </g>
+
+      <g
+          id="nested group - translate xy"
+          transform="translate(20, 30)">
+
+        <path
+            d="M 150,200 l -50,25"
+            fill="black"
+            stroke="black"
+            stroke-width="3"
+            test:name="path05"/>
+
+      </g>
+
+    </g>
+
+    <g
+        id="scale xy group"
+        transform="scale(0.5 1.5)">
+
+      <path
+          d="M 122,320 l -50,0"
+          fill="black"
+          stroke="black"
+          stroke-width="3"
+          test:name="path06"/>
+
+    </g>
+
+    <g
+        id="rotate group"
+        transform="rotate(20)">
+
+      <path
+          d="M 183,183 l 0,30"
+          fill="black"
+          stroke="black"
+          stroke-width="3"
+          test:name="path07"/>
+
+    </g>
+
+    <g
+        id="rotate xy group"
+        transform="rotate(45 183 183)">
+
+      <path
+          d="M 183,183 l 0,30"
+          fill="black"
+          stroke="black"
+          stroke-width="3"
+          test:name="path08"/>
+
+    </g>
+
+    <g
+        id="skew x group"
+        transform="skewX(5)">
+
+      <path
+          d="M 183,183 l 40,40"
+          fill="black"
+          stroke="black"
+          stroke-width="3"
+          test:name="path09"/>
+
+    </g>
+
+    <g
+        id="skew y group"
+        transform="skewY(5)">
+
+      <path
+          d="M 183,183 l 40,40"
+          fill="black"
+          stroke="black"
+          stroke-width="3"
+          test:name="path10"/>
+
+      <path
+          d="M 180,20 l -70,80"
+          fill="black"
+          stroke="black"
+          stroke-width="4"
+          transform="rotate(-40, 100, 100)"
+          test:name="path11"/>
+
+    </g>
+
+  </g>
+
+</svg>

test/test_groups.py

@@ -0,0 +1,192 @@
+from __future__ import division, absolute_import, print_function
+import unittest
+from svgpathtools import *
+from os.path import join, dirname
+import numpy as np
+
+
+def get_desired_path(name, paths):
+    return next(p for p in paths if p.element.get('{some://testuri}name') == name)
+
+
+def column_vector(values):
+    input = []
+    for value in values:
+        input.append([value])
+    return np.matrix(input)
+
+
+class TestGroups(unittest.TestCase):
+
+    def check_values(self, v, z):
+        # Check that the components of 2D vector v match the components of complex number z
+        self.assertAlmostEqual(v[0], z.real)
+        self.assertAlmostEqual(v[1], z.imag)
+
+    def check_line(self, tf, v_s_vals, v_e_relative_vals, name, paths):
+        # Check that the endpoints of the line have been correctly transformed.
+        # * tf is the transform that should have been applied.
+        # * v_s_vals is a 2D list of the values of the line's start point
+        # * v_e_relative_vals is a 2D list of the values of the line's end point relative to the start point
+        # * name is the path name (value of the test:name attribute in the SVG document)
+        # * paths is the output of doc.flatten_all_paths()
+        v_s_vals.append(1.0)
+        v_e_relative_vals.append(0.0)
+        v_s = column_vector(v_s_vals)
+        v_e = v_s + column_vector(v_e_relative_vals)
+
+        actual = get_desired_path(name, paths)
+
+        self.check_values(tf.dot(v_s), actual.path.start)
+        self.check_values(tf.dot(v_e), actual.path.end)
+
+    def test_group_flatten(self):
+        # Test the Document.flatten_all_paths() function against the groups.svg test file.
+        # There are 12 paths in that file, with various levels of being nested inside of group transforms.
+        # The check_line function is used to reduce the boilerplate, since all the tests are very similar.
+        # This test covers each of the different types of transforms that are specified by the SVG standard.
+        doc = Document(join(dirname(__file__), 'groups.svg'))
+
+        result = doc.flatten_all_paths()
+        self.assertEqual(12, len(result))
+
+        tf_matrix_group = np.matrix([[1.5, 0.0, -40.0], [0.0, 0.5, 20.0], [0.0, 0.0, 1.0]])
+
+        self.check_line(tf_matrix_group,
+                        [183, 183], [0.0, -50],
+                        'path00', result)
+
+        tf_scale_group = np.matrix([[1.25, 0.0, 0.0], [0.0, 1.25, 0.0], [0.0, 0.0, 1.0]])
+
+        self.check_line(tf_matrix_group.dot(tf_scale_group),
+                        [122, 320], [-50.0, 0.0],
+                        'path01', result)
+
+        self.check_line(tf_matrix_group.dot(tf_scale_group),
+                        [150, 200], [-50, 25],
+                        'path02', result)
+
+        self.check_line(tf_matrix_group.dot(tf_scale_group),
+                        [150, 200], [-50, 25],
+                        'path03', result)
+
+        tf_nested_translate_group = np.matrix([[1, 0, 20], [0, 1, 0], [0, 0, 1]])
+
+        self.check_line(tf_matrix_group.dot(tf_scale_group).dot(tf_nested_translate_group),
+                        [150, 200], [-50, 25],
+                        'path04', result)
+
+        tf_nested_translate_xy_group = np.matrix([[1, 0, 20], [0, 1, 30], [0, 0, 1]])
+
+        self.check_line(tf_matrix_group.dot(tf_scale_group).dot(tf_nested_translate_xy_group),
+                        [150, 200], [-50, 25],
+                        'path05', result)
+
+        tf_scale_xy_group = np.matrix([[0.5, 0, 0], [0, 1.5, 0.0], [0, 0, 1]])
+
+        self.check_line(tf_matrix_group.dot(tf_scale_xy_group),
+                        [122, 320], [-50, 0],
+                        'path06', result)
+
+        a_07 = 20.0*np.pi/180.0
+        tf_rotate_group = np.matrix([[np.cos(a_07), -np.sin(a_07), 0],
+                                     [np.sin(a_07),  np.cos(a_07), 0],
+                                     [0, 0, 1]])
+
+        self.check_line(tf_matrix_group.dot(tf_rotate_group),
+                        [183, 183], [0, 30],
+                        'path07', result)
+
+        a_08 = 45.0*np.pi/180.0
+        tf_rotate_xy_group_R = np.matrix([[np.cos(a_08), -np.sin(a_08), 0],
+                                          [np.sin(a_08),  np.cos(a_08), 0],
+                                          [0, 0, 1]])
+        tf_rotate_xy_group_T = np.matrix([[1, 0, 183], [0, 1, 183], [0, 0, 1]])
+        tf_rotate_xy_group = tf_rotate_xy_group_T.dot(tf_rotate_xy_group_R).dot(np.linalg.inv(tf_rotate_xy_group_T))
+
+        self.check_line(tf_matrix_group.dot(tf_rotate_xy_group),
+                        [183, 183], [0, 30],
+                        'path08', result)
+
+        a_09 = 5.0*np.pi/180.0
+        tf_skew_x_group = np.matrix([[1, np.tan(a_09), 0], [0, 1, 0], [0, 0, 1]])
+
+        self.check_line(tf_matrix_group.dot(tf_skew_x_group),
+                        [183, 183], [40, 40],
+                        'path09', result)
+
+        a_10 = 5.0*np.pi/180.0
+        tf_skew_y_group = np.matrix([[1, 0, 0], [np.tan(a_10), 1, 0], [0, 0, 1]])
+
+        self.check_line(tf_matrix_group.dot(tf_skew_y_group),
+                        [183, 183], [40, 40],
+                        'path10', result)
+
+        # This last test is for handling transforms that are defined as attributes of a <path> element.
+        a_11 = -40*np.pi/180.0
+        tf_path11_R = np.matrix([[np.cos(a_11), -np.sin(a_11), 0],
+                                 [np.sin(a_11),  np.cos(a_11), 0],
+                                 [0, 0, 1]])
+        tf_path11_T = np.matrix([[1, 0, 100], [0, 1, 100], [0, 0, 1]])
+        tf_path11 = tf_path11_T.dot(tf_path11_R).dot(np.linalg.inv(tf_path11_T))
+
+        self.check_line(tf_matrix_group.dot(tf_skew_y_group).dot(tf_path11),
+                        [180, 20], [-70, 80],
+                        'path11', result)
+
+    def check_group_count(self, doc, expected_count):
+        count = 0
+        for group in doc.tree.getroot().iter('{{{0}}}g'.format(SVG_NAMESPACE['svg'])):
+            count += 1
+
+        self.assertEqual(expected_count, count)
+
+    def test_add_group(self):
+        # Test the Document.add_group() function and related Document functions.
+        doc = Document(None)
+        self.check_group_count(doc, 0)
+
+        base_group = doc.add_group()
+        base_group.set('id', 'base_group')
+        self.assertTrue(doc.contains_group(base_group))
+        self.check_group_count(doc, 1)
+
+        child_group = doc.add_group(parent=base_group)
+        child_group.set('id', 'child_group')
+        self.assertTrue(doc.contains_group(child_group))
+        self.check_group_count(doc, 2)
+
+        grandchild_group = doc.add_group(parent=child_group)
+        grandchild_group.set('id', 'grandchild_group')
+        self.assertTrue(doc.contains_group(grandchild_group))
+        self.check_group_count(doc, 3)
+
+        sibling_group = doc.add_group(parent=base_group)
+        sibling_group.set('id', 'sibling_group')
+        self.assertTrue(doc.contains_group(sibling_group))
+        self.check_group_count(doc, 4)
+
+        # Test that we can retrieve each new group from the document
+        self.assertEqual(base_group, doc.get_or_add_group(['base_group']))
+        self.assertEqual(child_group, doc.get_or_add_group(['base_group', 'child_group']))
+        self.assertEqual(grandchild_group, doc.get_or_add_group(['base_group', 'child_group', 'grandchild_group']))
+        self.assertEqual(sibling_group, doc.get_or_add_group(['base_group', 'sibling_group']))
+
+        # Create a new nested group
+        new_child = doc.get_or_add_group(['base_group', 'new_parent', 'new_child'])
+        self.check_group_count(doc, 6)
+        self.assertEqual(new_child, doc.get_or_add_group(['base_group', 'new_parent', 'new_child']))
+
+        new_leaf = doc.get_or_add_group(['base_group', 'new_parent', 'new_child', 'new_leaf'])
+        self.assertEqual(new_leaf, doc.get_or_add_group(['base_group', 'new_parent', 'new_child', 'new_leaf']))
+        self.check_group_count(doc, 7)
+
+        path_d = 'M 206.07112,858.41289 L 206.07112,-2.02031 C -50.738,-81.14814 -20.36402,-105.87055 ' \
+                 '52.52793,-101.01525 L 103.03556,0.0 L 0.0,111.11678'
+
+        svg_path = doc.add_path(path_d, group=new_leaf)
+        self.assertEqual(path_d, svg_path.get('d'))
+
+        path = parse_path(path_d)
+        svg_path = doc.add_path(path, group=new_leaf)
+        self.assertEqual(path_d, svg_path.get('d'))

test/test_parsing.py

@@ -3,6 +3,20 @@
 from __future__ import division, absolute_import, print_function
 import unittest
 from svgpathtools import *
+import svgpathtools
+import numpy as np
+
+
+def construct_rotation_tf(a, x, y):
+    a = a * np.pi / 180.0
+    tf_offset = np.identity(3)
+    tf_offset[0:2, 2:3] = np.matrix([[x], [y]])
+    tf_rotate = np.identity(3)
+    tf_rotate[0:2, 0:2] = np.matrix([[np.cos(a), -np.sin(a)], [np.sin(a), np.cos(a)]])
+    tf_offset_neg = np.identity(3)
+    tf_offset_neg[0:2, 2:3] = np.matrix([[-x], [-y]])
+
+    return tf_offset.dot(tf_rotate).dot(tf_offset_neg)
 
 
 class TestParser(unittest.TestCase):
@@ -137,3 +151,67 @@ class TestParser(unittest.TestCase):
 
     def test_errors(self):
         self.assertRaises(ValueError, parse_path, 'M 100 100 L 200 200 Z 100 200')
+
+
+    def test_transform(self):
+
+        tf_matrix = svgpathtools.parser.parse_transform('matrix(1.0 2.0 3.0 4.0 5.0 6.0)')
+        expected_tf_matrix = np.identity(3)
+        expected_tf_matrix[0:2, 0:3] = np.matrix([[1.0, 3.0, 5.0], [2.0, 4.0, 6.0]])
+        self.assertTrue(np.array_equal(expected_tf_matrix, tf_matrix))
+
+        # Try a test with no y specified
+        expected_tf_translate = np.identity(3)
+        expected_tf_translate[0, 2] = -36
+        self.assertTrue(np.array_equal(
+            expected_tf_translate,
+            svgpathtools.parser.parse_transform('translate(-36)')
+        ))
+
+        # Now specify y
+        expected_tf_translate[1, 2] = 45.5
+        tf_translate = svgpathtools.parser.parse_transform('translate(-36 45.5)')
+        self.assertTrue(np.array_equal(expected_tf_translate, tf_translate))
+
+        # Try a test with no y specified
+        expected_tf_scale = np.identity(3)
+        expected_tf_scale[0, 0] = 10
+        expected_tf_scale[1, 1] = 10
+        self.assertTrue(np.array_equal(
+            expected_tf_scale,
+            svgpathtools.parser.parse_transform('scale(10)')
+        ))
+
+        # Now specify y
+        expected_tf_scale[1, 1] = 0.5
+        tf_scale = svgpathtools.parser.parse_transform('scale(10 0.5)')
+        self.assertTrue(np.array_equal(expected_tf_scale, tf_scale))
+
+        tf_rotation = svgpathtools.parser.parse_transform('rotate(-10 50 100)')
+        expected_tf_rotation = construct_rotation_tf(-10, 50, 100)
+        self.assertTrue(np.array_equal(expected_tf_rotation, tf_rotation))
+
+        # Try a test with no offset specified
+        self.assertTrue(np.array_equal(
+            construct_rotation_tf(50, 0, 0),
+            svgpathtools.parser.parse_transform('rotate(50)')
+        ))
+
+        expected_tf_skewx = np.identity(3)
+        expected_tf_skewx[0, 1] = np.tan(40.0 * np.pi/180.0)
+        tf_skewx = svgpathtools.parser.parse_transform('skewX(40)')
+        self.assertTrue(np.array_equal(expected_tf_skewx, tf_skewx))
+
+        expected_tf_skewy = np.identity(3)
+        expected_tf_skewy[1, 0] = np.tan(30.0 * np.pi / 180.0)
+        tf_skewy = svgpathtools.parser.parse_transform('skewY(30)')
+        self.assertTrue(np.array_equal(expected_tf_skewy, tf_skewy))
+
+        self.assertTrue(np.array_equal(
+            tf_rotation.dot(tf_translate).dot(tf_skewx).dot(tf_scale),
+            svgpathtools.parser.parse_transform(
+                """rotate(-10 50 100)
+                   translate(-36 45.5)
+                   skewX(40)
+                   scale(10 0.5)""")
+        ))