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Preserve custom spring force and torque callbacks when copying #317

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Merged
viblo merged 1 commit into from
Oct 12, 2026
Merged

Preserve custom spring force and torque callbacks when copying #317

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4 changes: 4 additions & 0 deletions pymunk/constraints.py
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Original file line number Diff line number Diff line change
Expand Up @@ -578,6 +578,8 @@ class DampedSpring(Constraint):
"damping",
]

_pickle_attrs_general = Constraint._pickle_attrs_general + ["force_func"]

_pickle_attrs_skip = Constraint._pickle_attrs_skip + ["_force_func"]

def __init__(
Expand Down Expand Up @@ -707,6 +709,8 @@ class DampedRotarySpring(Constraint):
"damping",
]

_pickle_attrs_general = Constraint._pickle_attrs_general + ["torque_func"]

_pickle_attrs_skip = Constraint._pickle_attrs_skip + ["_torque_func"]

_torque_func: Optional[_TorqueFunc] = None
Expand Down
61 changes: 61 additions & 0 deletions pymunk/tests/test_constraint.py
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
import copy
import gc
import pickle
import unittest
Expand Down Expand Up @@ -418,6 +419,32 @@ def test_pickle(self) -> None:
self.assertEqual(j.a.mass, j2.a.mass)
self.assertEqual(j.b.mass, j2.b.mass)

def test_copy_force_func(self) -> None:
a, b = p.Body(10, 10), p.Body(20, 20)
b.position = (3, 0)
j = DampedSpring(a, b, (0, 0), (0, 0), 1, 2, 0)
j.force_func = nonlinear_spring_force
for clone in (
j.copy,
lambda: copy.deepcopy(j),
lambda: pickle.loads(pickle.dumps(j)),
):
with self.subTest(clone=clone):
j2 = clone()
self.assertIs(j2.force_func, nonlinear_spring_force)
space = p.Space()
space.add(j2.a, j2.b, j2)
space.step(0.125)
self.assertEqual(j2.impulse, -2)

j.force_func = DampedSpring.spring_force
j2 = pickle.loads(pickle.dumps(j))
self.assertIs(j2.force_func, DampedSpring.spring_force)
space = p.Space()
space.add(j2.a, j2.b, j2)
space.step(0.125)
self.assertEqual(j2.impulse, -0.5)


class UnitTestDampedRotarySpring(unittest.TestCase):
def test_rest_angle(self) -> None:
Expand Down Expand Up @@ -478,6 +505,32 @@ def test_pickle(self) -> None:
self.assertEqual(j.a.mass, j2.a.mass)
self.assertEqual(j.b.mass, j2.b.mass)

def test_copy_torque_func(self) -> None:
a, b = p.Body(10, 10), p.Body(20, 20)
b.angle = 2
j = DampedRotarySpring(a, b, 0, 2, 0)
j.torque_func = nonlinear_spring_torque
for clone in (
j.copy,
lambda: copy.deepcopy(j),
lambda: pickle.loads(pickle.dumps(j)),
):
with self.subTest(clone=clone):
j2 = clone()
self.assertIs(j2.torque_func, nonlinear_spring_torque)
space = p.Space()
space.add(j2.a, j2.b, j2)
space.step(0.125)
self.assertEqual(j2.impulse, -2)

j.torque_func = DampedRotarySpring.spring_torque
j2 = pickle.loads(pickle.dumps(j))
self.assertIs(j2.torque_func, DampedRotarySpring.spring_torque)
space = p.Space()
space.add(j2.a, j2.b, j2)
space.step(0.125)
self.assertEqual(j2.impulse, -0.5)


class UnitTestRotaryLimitJoint(unittest.TestCase):
def test_min(self) -> None:
Expand Down Expand Up @@ -597,3 +650,11 @@ def pre_solve(c: Constraint, s: p.Space) -> None:

def post_solve(c: Constraint, s: p.Space) -> None:
pass


def nonlinear_spring_force(spring: DampedSpring, distance: float) -> float:
return spring.stiffness * (spring.rest_length - distance) ** 3


def nonlinear_spring_torque(spring: DampedRotarySpring, relative_angle: float) -> float:
return spring.stiffness * (relative_angle - spring.rest_angle) ** 3
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