SVG PathData Tools

The svgpdtools module defines utilities to manipulate pathdata (value of d attribute) of a SVG path-element. Also there is a command line interface.

Install

% pip install svgpdtools

Examples

import xml.etree.ElementTree as ET
import svgpdtools as PD

def apply_translates():
    PD.precision(3)
    tree = ET.parse('infile.svg')
    t_parent = PD.Transform.translate(25, 25)
    for path in tree.findall('.//{*}path'):
        pd = PD.pathdata_from_string(path.get('d'))
        t_child = path.get('transform', '')
        if t_child:
            path.set('transform', '')
        pd.transform(t_parent * PD.transform_from_string(t_child))
        path.set('d', str(pd))
    ET.register_namespace('', 'http://www.w3.org/2000/svg')
    tree.write('outfile.svg', encoding='utf-8')

Below is using CLI to get almost equivalent output as the above code.

With the CLI to handle SVG data, this module uses ‘xml.sax.make_parser’ and ‘xml.sax.saxutils.XMLGenerator’. So you should not parse untrusted data.

% svgpdtools normalize --collapse-transform-attribute -f infile.svg |\
      svgpdtools transform -p 3 "translate(25,25)" > outfile.svg

Module contents

svgpdtools.precision(value: int) -> None

Set the max length of fractional part of a real number. The default value is 6. Each coordinate of the pathdata is calculated as a Python float value, and formatted with that length when shown.

svgpdtools.pathdata_from_string(src: str) -> PathData

Convert a pathdata string to a svgpdtools.PathData object. A pathdata string is a value of the d property of the SVG-path element.

svgpdtools.transform_from_string(src: str) -> Transform

Convert a string representation of SVG transfom functions to a svgpdtools.Transform object. The syntax of transform functions are the same as the SVG transform attribute.

class svgpdtools.PathData

UserList of svgpdtools.Command objects. This class has some methods which are major task of the svgpdtools module. transform(), absolutize(), and normalize(), those methods are destructive operations.

class svgpdtools.Transform

This class represents a transform matrix, which is the same as the SVG's presentation attribute transform. Transform functions are provided as static functions. Each function's syntax is also same as the SVG's transform functions.

• Transform.matrix(a, b, c, d, e, f)
• Transform.translate(dx, dy)
• Transform.scale(sx, sy)
• Transform.rotate(deg, cx, cy)
• Transform.skewX(deg)
• Transform.skewY(deg)

For example, the current transformation matrix (CTM) is represent multiple functions in SVG:

<g transform="translate(10,10) rotate(45) translate(-10,-10)">
  ...
</g>

The above transformation of the SVGGElement is equivalent to the following:

import svgpdtools.Transform as T
T1, T2, T3 = T.translate(10,10), T.rotate(45), T.translate(-10,-10)
ctm = T1 * T2 * T3
# or
ctm = T.concat([T1, T2, T3])
# or
ctm = T1.concatenated(T2, T3)

svgpdtools.Transform() is an identity matrix.

Future considerations

• Change the PathData object to a immutable object.
• Implement editing functions that common bezier path tools have.