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",
... ]
>>> def sample_func(point):
...     x = int(point[0])
...     y = int(point[1])
...     return 1 if img[y][x] == "x" else 0

>>> pl_set = march_soft(pymunk.BB(0,0,6,6), 7, 7, .5, sample_func)
>>> print(len(pl_set))
2

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

>>> s = pymunk.Space()
>>> for poly_line in pl_set:
...     for i in range(len(poly_line) - 1):
...         a = poly_line[i]
...         b = poly_line[i + 1]
...         segment = pymunk.Segment(s.static_body, a, b, 1)  
...         s.add(segment)

class pymunk.autogeometry.PolylineSet

Bases: Sequence[List[Vec2d]]

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__() → None

Initalize a new PolylineSet

collect_segment(v0: Tuple[float, float], v1: Tuple[float, float]) → None

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

pymunk.autogeometry.convex_decomposition(polyline: List[Tuple[float, float]] | List[Vec2d], tolerance: float) → List[List[Vec2d]]

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)]

pymunk.autogeometry.is_closed(polyline: List[Tuple[float, float]] | List[Vec2d]) → bool

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

Parameters:

polyline ([(float,float)]) – Polyline to simplify.

Return type:

bool

pymunk.autogeometry.march_hard(bb: BB, x_samples: int, y_samples: int, threshold: float, sample_func: Callable[[Tuple[float, float]], float]) → PolylineSet

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

• sample_func (func(point: Tuple[float, float]) -> float) – The sample function will be called for x_samples * y_samples spread across the bounding box area, and should return a float.

Returns:

PolylineSet with the polylines found.

pymunk.autogeometry.march_soft(bb: BB, x_samples: int, y_samples: int, threshold: float, sample_func: Callable[[Tuple[float, float]], float]) → PolylineSet

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

• sample_func (func(point: Tuple[float, float]) -> float) – The sample function will be called for x_samples * y_samples spread across the bounding box area, and should return a float.

Returns:

PolylineSet with the polylines found.

pymunk.autogeometry.simplify_curves(polyline: List[Tuple[float, float]] | List[Vec2d], tolerance: float) → List[Vec2d]

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: List[Tuple[float, float]] | List[Vec2d], tolerance: float) → List[Vec2d]

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: List[Tuple[float, float]] | List[Vec2d], tolerance: float) → List[Vec2d]

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)]