__docformat__ = "reStructuredText"
from typing import TYPE_CHECKING, Tuple, Dict, List, Any, Iterable, Sequence
if TYPE_CHECKING:
from .space import Space
from .shapes import Shape
from ._chipmunk_cffi import ffi, lib
from .contact_point_set import ContactPointSet
from .vec2d import Vec2d
[docs]
class Arbiter(object):
"""The Arbiter object encapsulates a pair of colliding shapes and all of
the data about their collision.
They are created when a collision starts, and persist until those
shapes are no longer colliding.
.. Warning::
Because arbiters are handled by the space you should never
hold onto a reference to an arbiter as you don't know when it will be
destroyed! Use them within the callback where they are given to you
and then forget about them or copy out the information you need from
them.
"""
[docs]
def __init__(self, _arbiter: ffi.CData, space: "Space") -> None:
"""Initialize an Arbiter object from the Chipmunk equivalent struct
and the Space.
.. note::
You should never need to create an instance of this class directly.
"""
self._arbiter = _arbiter
self._space = space
def _get_contact_point_set(self) -> ContactPointSet:
_set = lib.cpArbiterGetContactPointSet(self._arbiter)
return ContactPointSet._from_cp(_set)
def _set_contact_point_set(self, point_set: ContactPointSet) -> None:
# This has to be done by fetching a new Chipmunk point set, update it
# according to whats passed in and the pass that back to chipmunk due
# to the fact that ContactPointSet doesnt contain a reference to the
# corresponding c struct.
_set = lib.cpArbiterGetContactPointSet(self._arbiter)
_set.normal = point_set.normal
if len(point_set.points) == _set.count:
for i in range(_set.count):
_set.points[i].pointA = point_set.points[0].point_a
_set.points[i].pointB = point_set.points[0].point_b
_set.points[i].distance = point_set.points[0].distance
else:
msg = "Expected {} points, got {} points in point_set".format(
_set.count, len(point_set.points)
)
raise Exception(msg)
lib.cpArbiterSetContactPointSet(self._arbiter, ffi.addressof(_set))
contact_point_set = property(
_get_contact_point_set,
_set_contact_point_set,
doc="""Contact point sets make getting contact information from the
Arbiter simpler.
Return `ContactPointSet`""",
)
@property
def shapes(self) -> Tuple["Shape", "Shape"]:
"""Get the shapes in the order that they were defined in the
collision handler associated with this arbiter
"""
shapeA_p = ffi.new("cpShape *[1]")
shapeB_p = ffi.new("cpShape *[1]")
lib.cpArbiterGetShapes(self._arbiter, shapeA_p, shapeB_p)
a, b = self._space._get_shape(shapeA_p[0]), self._space._get_shape(shapeB_p[0])
assert a is not None
assert b is not None
return a, b
def _get_restitution(self) -> float:
return lib.cpArbiterGetRestitution(self._arbiter)
def _set_restitution(self, restitution: float) -> None:
lib.cpArbiterSetRestitution(self._arbiter, restitution)
restitution = property(
_get_restitution,
_set_restitution,
doc="""The calculated restitution (elasticity) for this collision
pair.
Setting the value in a pre_solve() callback will override the value
calculated by the space. The default calculation multiplies the
elasticity of the two shapes together.
""",
)
def _get_friction(self) -> float:
return lib.cpArbiterGetFriction(self._arbiter)
def _set_friction(self, friction: float) -> None:
lib.cpArbiterSetFriction(self._arbiter, friction)
friction = property(
_get_friction,
_set_friction,
doc="""The calculated friction for this collision pair.
Setting the value in a pre_solve() callback will override the value
calculated by the space. The default calculation multiplies the
friction of the two shapes together.
""",
)
def _get_surface_velocity(self) -> Vec2d:
v = lib.cpArbiterGetSurfaceVelocity(self._arbiter)
return Vec2d(v.x, v.y)
def _set_surface_velocity(self, velocity: Vec2d) -> None:
lib.cpArbiterSetSurfaceVelocity(self._arbiter, velocity)
surface_velocity = property(
_get_surface_velocity,
_set_surface_velocity,
doc="""The calculated surface velocity for this collision pair.
Setting the value in a pre_solve() callback will override the value
calculated by the space. the default calculation subtracts the
surface velocity of the second shape from the first and then projects
that onto the tangent of the collision. This is so that only
friction is affected by default calculation. Using a custom
calculation, you can make something that responds like a pinball
bumper, or where the surface velocity is dependent on the location
of the contact point.
""",
)
@property
def total_impulse(self) -> Vec2d:
"""Returns the impulse that was applied this step to resolve the
collision.
This property should only be called from a post-solve or each_arbiter
callback.
"""
v = lib.cpArbiterTotalImpulse(self._arbiter)
return Vec2d(v.x, v.y)
@property
def total_ke(self) -> float:
"""The amount of energy lost in a collision including static, but
not dynamic friction.
This property should only be called from a post-solve or each_arbiter callback.
"""
return lib.cpArbiterTotalKE(self._arbiter)
@property
def is_first_contact(self) -> bool:
"""Returns true if this is the first step the two shapes started
touching.
This can be useful for sound effects for instance. If its the first
frame for a certain collision, check the energy of the collision in a
post_step() callback and use that to determine the volume of a sound
effect to play.
"""
return bool(lib.cpArbiterIsFirstContact(self._arbiter))
@property
def is_removal(self) -> bool:
"""Returns True during a separate() callback if the callback was
invoked due to an object removal.
"""
return bool(lib.cpArbiterIsRemoval(self._arbiter))
@property
def normal(self) -> Vec2d:
"""Returns the normal of the collision."""
v = lib.cpArbiterGetNormal(self._arbiter)
return Vec2d(v.x, v.y)
def _contacts_to_dicts(
_contacts: Sequence[ffi.CData], count: int
) -> List[Dict[str, Any]]:
res = []
for i in range(count):
res.append(_contact_to_dict(_contacts[i]))
return res
def _contact_to_dict(_contact: ffi.CData) -> Dict[str, Any]:
d = {}
d["r1"] = _contact.r1.x, _contact.r1.y
d["r2"] = _contact.r2.x, _contact.r2.y
d["nMass"] = _contact.nMass
d["tMass"] = _contact.tMass
d["bounce"] = _contact.bounce
d["jnAcc"] = _contact.jnAcc
d["jtAcc"] = _contact.jtAcc
d["jBias"] = _contact.jBias
d["bias"] = _contact.bias
d["hash"] = _contact.hash
return d
def _contacts_from_dicts(ds: Sequence[Dict[str, Any]]) -> List[ffi.CData]:
_contacts = lib.cpContactArrAlloc(len(ds))
for i in range(len(ds)):
_contact = _contacts[i]
d = ds[i]
_contact.r1.x = d["r1"][0]
_contact.r1.y = d["r1"][1]
_contact.r2.x = d["r2"][0]
_contact.r2.y = d["r2"][1]
_contact.nMass = d["nMass"]
_contact.tMass = d["tMass"]
_contact.bounce = d["bounce"]
_contact.jnAcc = d["jnAcc"]
_contact.jtAcc = d["jtAcc"]
_contact.jBias = d["jBias"]
_contact.bias = d["bias"]
_contact.hash = d["hash"]
return _contacts
def _arbiter_from_dict(d: Dict[str, Any], space: "Space") -> ffi.CData:
_arb = lib.cpArbiterNew(
d["a"]._shape, d["b"]._shape
) # this will also set the bodies
_arb.e = d["e"]
_arb.u = d["u"]
_arb.surface_vr = d["surface_vr"]
_arb.count = d["count"]
_arb.contacts = _contacts_from_dicts(d["contacts"])
_arb.n = d["n"]
_arb.swapped = d["swapped"]
_arb.stamp = d["stamp"]
_arb.state = d["state"]
return _arb
def _arbiter_to_dict(_arbiter: ffi.CData, space: "Space") -> Dict[str, Any]:
d = {}
d["e"] = _arbiter.e
d["u"] = _arbiter.u
d["surface_vr"] = (_arbiter.surface_vr.x, _arbiter.surface_vr.y)
cp_bodies = {}
cp_shapes = {}
for body in space.bodies:
cp_bodies[body._body] = body
for shape in space.shapes:
cp_shapes[shape._shape] = shape
# cpDataPointer data;
d["a"] = cp_shapes[_arbiter.a]
d["b"] = cp_shapes[_arbiter.b]
# these are not needed, since they can be fetched from the shapes
# d['body_a'] = cp_bodies[_arbiter.body_a]
# d['body_b'] = cp_bodies[_arbiter.body_b]
# struct cpArbiterThread thread_a, thread_b;
d["count"] = _arbiter.count
d["contacts"] = _contacts_to_dicts(_arbiter.contacts, _arbiter.count)
d["n"] = _arbiter.n.x, _arbiter.n.y
# // Regular, wildcard A and wildcard B collision handlers.
# cpCollisionHandler *handler, *handlerA, *handlerB;
d["swapped"] = _arbiter.swapped
d["stamp"] = _arbiter.stamp
d["state"] = _arbiter.state
return d
