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svg.path 2.1.1

SVG path objects and parser

svg.path

svg.path is a collection of objects that implement the different path commands in SVG, and a parser for SVG path definitions.

Usage

There are four path segment objects, Line, Arc, CubicBezier and QuadraticBezier.`There is also a Path object that acts as a collection of the path segment objects.

All coordinate values for these classes are given as complex values, where the .real part represents the X coordinate, and the .imag part representes the Y coordinate.

>>> from svg.path import Path, Line, Arc, CubicBezier, QuadraticBezier

All of these objects have a .point() function which will return the coordinates of a point on the path, where the point is given as a floating point value where 0.0 is the start of the path and 1.0 is end end.

You can calculate the length of a Path or it’s segments with the .length() function. For CubicBezier and Arc segments this is done by geometric approximation and for this reason may be very slow. You can make it faster by passing in an error option to the method. If you don’t pass in error, it defaults to 1e-12.

>>> CubicBezier(300+100j, 100+100j, 200+200j, 200+300j).length(error=1e-5)
297.2208145656899

CubicBezier and Arc also has a min_depth option that specifies the minimum recursion depth. This is set to 5 by default, resulting in using a minimum of 32 segments for the calculation. Setting it to 0 is a bad idea for CubicBeziers, as they may become approximated to a straight line.

Line.length() and QuadraticBezier.length() also takes these parameters, but they are ignored.

CubicBezier and QuadraticBezier also has is_smooth_from(previous) methods, that check if the segment is a “smooth” segment compared to the given segment.

There is also a parse_path() function that will take an SVG path definition and return a Path object.

>>> from svg.path import parse_path
>>> parse_path('M 100 100 L 300 100')
Path(Line(start=(100+100j), end=(300+100j)), closed=False)

Classes

These are the SVG path segment classes. See the SVG specifications for more information on what each parameter means.

  • Line(start, end)
  • Arc(start, radius, rotation, arc, sweep, end)
  • QuadraticBezier(start, control, end)
  • CubicBezier(start, control1, control2, end)

In addition to that, there is the Path class, which is instantiated with a sequence of path segments:

  • Path(*segments)

The Path class is a mutable sequence, so it behaves like a list. You can add to it and replace path segments etc.

>>> path = Path(Line(100+100j,300+100j), Line(100+100j,300+100j))
>>> path.append(QuadraticBezier(300+100j, 200+200j, 200+300j))
>>> path[0] = Line(200+100j,300+100j)
>>> del path[1]

The path object also has a d() method that will return the SVG representation of the Path segments.

>>> path.d()
'M 200,100 L 300,100 Q 200,200 200,300'

Examples

This SVG path example draws a triangle:

>>> path1 = parse_path('M 100 100 L 300 100 L 200 300 z')

You can format SVG paths in many different ways, all valid paths should be accepted:

>>> path2 = parse_path('M100,100L300,100L200,300z')

And these paths should be equal:

>>> path1 == path2
True

You can also build a path from objects:

>>> path3 = Path(Line(100+100j,300+100j), Line(300+100j, 200+300j), Line(200+300j, 100+100j))

And it should again be equal to the first path:

>>> path1 == path2
True

Paths are mutable sequences, you can slice and append:

>>> path1.append(QuadraticBezier(300+100j, 200+200j, 200+300j))
>>> len(path1[2:]) == 2
True

Paths also have a closed property, which defines if the path should be seen as a closed path or not.

>>> path = parse_path('M100,100L300,100L200,300z')
>>> path.closed
True

If you modify the path in such a way that it is no longer closeable, it will not be closed.

>>> path[0].start = (100+150j)
>>> path.closed
False

However, a path previously set as closed will automatically close if it it further modified to that it can be closed.

>>> path[-1].end = (300+100j)
>>> path.closed
True

Trying to set a Path to be closed if the end does not coincide with the start of any segment will raise an error.

>>> path = parse_path('M100,100L300,100L200,300')
>>> path.closed = True
Traceback (most recent call last):
...
ValueError: End does not coincide with a segment start.

Future features

  • Reversing paths. They should then reasonably be drawn “backwards” meaning each path segment also needs to be reversed.
  • Mathematical transformations might make sense.

Licence

This module is under a MIT License.

Contributors

Lennart Regebro <regebro@gmail.com>, Original Author

Justin Gruenberg implemented the Quadradic Bezier calculations and provided suggestions and feedback about the d() function.

Michiel Schallig suggested calculating length by recursive straight-line approximations, which enables you to choose between accuracy or speed. Steve Schwarz added an error argument to make that choice an argument.

Thanks also to bug fixers Martin R, abcjjy, Daniel Stender and MTician.

Changelog

2.1.1 (2016-02-28)

  • #18: QuadraticBeziers could get a DivideByZero error under certain circumstances. [MTician]
  • Accept an error parameter to Path.point() to be able to control error vs performance setting. [saschwarz]
  • #25: Arc’s could create a MathDomain error under certain circumstances.
  • #17: Set last_command always.

2.0.1 (2015-10-17)

  • #20: The doctext for the closed() setter was incorrect.
  • #19: Fixed so tests didn’t use relative paths. [danstender]

2.0 (2015-05-15)

  • Nothing changed yet.

2.0b1 (2014-11-06)

  • Added a Path.d() function to generate the Path’s d attribute.
  • Added is_smooth_from() on QubicBezier and QuadradicBezier.
  • Path()’s now have a .closed property.
  • Fixed the representation so it’s parseable.
  • The calculations for CubicBezier and Arc segments are now recursive, and will end when a specific accuracy has been achieved. This is somewhat faster for Arcs and somewhat slower for CubicBezier. However, you can now specify an accuracy, so if you want faster but looser calculations, you can have that.
  • ‘t’ segments (smooth, relative QuadraticBeziers) whose previous segment was not a QuadraticBezier would get an incorrect control point.

1.2 (2014-11-01)

  • New Quadradic Bezier implementation. [Justin Gruenberg]
  • Solved issue #6: Z close path behavior. [abcjjy]

1.1 (2013-10-19)

  • Floats with negative exponents work again.
  • New tokenizer that is around 20 times faster.

1.0 (2013-05-28)

  • Solved issue #2: Paths with negative values and no spaces didn’t work. [regebro]

1.0b1 (2013-02-03)

  • Original release.
 
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