pymunk.autogeometry Module

This module contain functions for automatic generation of geometry, for example from an image.

Example:

>>> import pymunk
>>> from pymunk.autogeometry import march_soft
>>> img = [
...     "  xx   ",
...     "  xx   ",
...     "  xx   ",
...     "  xx   ",
...     "  xx   ",
...     "  xxxxx",
...     "  xxxxx",
... ]
>>> segments = []

>>> def segment_func(v0, v1):
...     segments.append((tuple(v0), tuple(v1)))
>>> def sample_func(point):
...     x = int(point.x)
...     y = int(point.y)
...     return 1 if img[y][x] == "x" else 0

>>> march_soft(pymunk.BB(0,0,6,6), 7, 7, .5, segment_func, sample_func)
>>> print(len(segments))
13

The information in segments can now be used to create geometry, for example as a Pymunk Poly or Segment:

>>> s = pymunk.Space()
>>> for (a,b) in segments:
...     segment = pymunk.Segment(s.static_body, a, b, 5)  
...     s.add(segment)
pymunk.autogeometry.is_closed(polyline)[source]

Returns true if the first vertex is equal to the last.

Parameters:polyline ([(float,float)]) – Polyline to simplify.
Return type:bool
pymunk.autogeometry.simplify_curves(polyline, tolerance)[source]

Returns a copy of a polyline simplified by using the Douglas-Peucker algorithm.

This works very well on smooth or gently curved shapes, but not well on straight edged or angular shapes.

Parameters:
  • polyline ([(float,float)]) – Polyline to simplify.
  • tolerance (float) – A higher value means more error is tolerated.
Return type:

[(float,float)]

pymunk.autogeometry.simplify_vertexes(polyline, tolerance)[source]

Returns a copy of a polyline simplified by discarding “flat” vertexes.

This works well on straight edged or angular shapes, not as well on smooth shapes.

Parameters:
  • polyline ([(float,float)]) – Polyline to simplify.
  • tolerance (float) – A higher value means more error is tolerated.
Return type:

[(float,float)]

pymunk.autogeometry.to_convex_hull(polyline, tolerance)[source]

Get the convex hull of a polyline as a looped polyline.

Parameters:
  • polyline ([(float,float)]) – Polyline to simplify.
  • tolerance (float) – A higher value means more error is tolerated.
Return type:

[(float,float)]

pymunk.autogeometry.convex_decomposition(polyline, tolerance)[source]

Get an approximate convex decomposition from a polyline.

Returns a list of convex hulls that match the original shape to within tolerance.

Note

If the input is a self intersecting polygon, the output might end up overly simplified.

Parameters:
  • polyline ([(float,float)]) – Polyline to simplify.
  • tolerance (float) – A higher value means more error is tolerated.
Return type:

[(float,float)]

class pymunk.autogeometry.PolylineSet[source]

Bases: _abcoll.Sequence

A set of Polylines.

Mainly intended to be used for its collect_segment() function when generating geometry with the march_soft() and march_hard() functions.

__init__()[source]
collect_segment(v0, v1)[source]

Add a line segment to a polyline set.

A segment will either start a new polyline, join two others, or add to or loop an existing polyline. This is mostly intended to be used as a callback directly from march_soft() or march_hard().

Parameters:
  • v0 ((float,float)) – Start of segment
  • v1 ((float,float)) – End of segment
count(value) → integer -- return number of occurrences of value
index(value) → integer -- return first index of value.

Raises ValueError if the value is not present.

pymunk.autogeometry.march_soft(bb, x_samples, y_samples, threshold, segment_func, sample_func)[source]

Trace an anti-aliased contour of an image along a particular threshold.

The given number of samples will be taken and spread across the bounding box area using the sampling function and context.

Parameters:
  • bb (BB) – Bounding box of the area to sample within
  • x_samples (int) – Number of samples in x
  • y_samples (int) – Number of samples in y
  • threshold (float) – A higher value means more error is tolerated
  • segment_func (func(v0 : Vec2d, v1 : Vec2d)) – The segment function will be called for each segment detected that lies along the density contour for threshold.
  • sample_func (func(point: Vec2d) -> float) – The sample function will be called for x_samples * y_samples spread across the bounding box area, and should return a float.
pymunk.autogeometry.march_hard(bb, x_samples, y_samples, threshold, segment_func, sample_func)[source]

Trace an aliased curve of an image along a particular threshold.

The given number of samples will be taken and spread across the bounding box area using the sampling function and context.

Parameters:
  • bb (BB) – Bounding box of the area to sample within
  • x_samples (int) – Number of samples in x
  • y_samples (int) – Number of samples in y
  • threshold (float) – A higher value means more error is tolerated
  • segment_func (func(v0 : Vec2d, v1 : Vec2d)) – The segment function will be called for each segment detected that lies along the density contour for threshold.
  • sample_func (func(point: Vec2d) -> float) – The sample function will be called for x_samples * y_samples spread across the bounding box area, and should return a float.