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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, Move, Line, Arc, CubicBezier, QuadraticBezier, Close

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 the 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(Move(to=(100+100j)), Line(start=(100+100j), end=(300+100j)))

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(Move(200+100j), Line(200+100j,100+200j), Line(100+200j,300+100j))
>>> path.append(QuadraticBezier(300+100j, 200+200j, 200+300j))
>>> path[0] = Move(200+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'

Note that there currently is no internal consistency checks when you manipulate lines this way. This path now has an internal representation that it's different from it's d() path. Notice how the Line() segment starts in a different location from where the Move() segments say. This may change in future releases, and the Path manipulation methods may be changed to ensure consistency.

>>> path
Path(Move(to=(200+100j)), Line(start=(100+200j), end=(300+100j)),
QuadraticBezier(start=(300+100j), control=(200+200j), end=(200+300j),
smooth=False))

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:]) == 3
True

Note that there is no protection against you creating paths that are invalid. You can for example have a Close command that doesn't end at the path start:

>>> wrong = Path(Line(100+100j,200+100j), Close(200+300j, 0))

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.
  • Verifying that paths are correct, or protection against creating incorrect paths.

License

This module is under a MIT License.