Source code for pymunk.body

__docformat__ = "reStructuredText"

from weakref import WeakSet
import copy
from . import _chipmunk_cffi
cp = _chipmunk_cffi.lib
ffi = _chipmunk_cffi.ffi    
from .vec2d import Vec2d
from .arbiter import Arbiter
from ._pickle import PickleMixin

[docs]class Body(PickleMixin, object): """A rigid body * Use forces to modify the rigid bodies if possible. This is likely to be the most stable. * Modifying a body's velocity shouldn't necessarily be avoided, but applying large changes can cause strange results in the simulation. Experiment freely, but be warned. * Don't modify a body's position every step unless you really know what you are doing. Otherwise you're likely to get the position/velocity badly out of sync. A Body can be copied and pickled. Sleeping bodies that are copied will be awake in the fresh copy. When a Body is copied any spaces, shapes or constraints attached to the body will not be copied. """ DYNAMIC = cp.CP_BODY_TYPE_DYNAMIC """Dynamic bodies are the default body type. They react to collisions, are affected by forces and gravity, and have a finite amount of mass. These are the type of bodies that you want the physics engine to simulate for you. Dynamic bodies interact with all types of bodies and can generate collision callbacks. """ KINEMATIC = cp.CP_BODY_TYPE_KINEMATIC """Kinematic bodies are bodies that are controlled from your code instead of inside the physics engine. They arent affected by gravity and they have an infinite amount of mass so they don't react to collisions or forces with other bodies. Kinematic bodies are controlled by setting their velocity, which will cause them to move. Good examples of kinematic bodies might include things like moving platforms. Objects that are touching or jointed to a kinematic body are never allowed to fall asleep. """ STATIC = cp.CP_BODY_TYPE_STATIC """Static bodies are bodies that never (or rarely) move. Using static bodies for things like terrain offers a big performance boost over other body types- because Chipmunk doesn't need to check for collisions between static objects and it never needs to update their collision information. Additionally, because static bodies don't move, Chipmunk knows it's safe to let objects that are touching or jointed to them fall asleep. Generally all of your level geometry will be attached to a static body except for things like moving platforms or doors. Every space provide a built-in static body for your convenience. Static bodies can be moved, but there is a performance penalty as the collision information is recalculated. There is no penalty for having multiple static bodies, and it can be useful for simplifying your code by allowing different parts of your static geometry to be initialized or moved separately. """ _pickle_attrs_init = ['mass', 'moment', 'body_type'] _pickle_attrs_general = ['force', 'angle', 'position', 'center_of_gravity', 'velocity', 'angular_velocity', 'torque'] _pickle_attrs_skip = ['is_sleeping', '_velocity_func', '_position_func']
[docs] def __init__(self, mass=0, moment=0, body_type=DYNAMIC): """Create a new Body Mass and moment are ignored when body_type is KINEMATIC or STATIC. Guessing the mass for a body is usually fine, but guessing a moment of inertia can lead to a very poor simulation so it's recommended to use Chipmunk's moment calculations to estimate the moment for you. There are two ways to set up a dynamic body. The easiest option is to create a body with a mass and moment of 0, and set the mass or density of each collision shape added to the body. Chipmunk will automatically calculate the mass, moment of inertia, and center of gravity for you. This is probably preferred in most cases. Note that these will only be correctly calculated after the body and shape are added to a space. The other option is to set the mass of the body when it's created, and leave the mass of the shapes added to it as 0.0. This approach is more flexible, but is not as easy to use. Don't set the mass of both the body and the shapes. If you do so, it will recalculate and overwrite your custom mass value when the shapes are added to the body. Examples of the different ways to set up the mass and moment: >>> import pymunk >>> radius = 2 >>> mass = 3 >>> density = 3 >>> def print_mass_moment(b): ... print("mass={:.0f} moment={:.0f}".format(b.mass, b.moment)) >>> # Using Shape.density >>> s = pymunk.Space() >>> b = pymunk.Body() >>> c = pymunk.Circle(b, radius) >>> c.density = density >>> print_mass_moment(b) mass=0 moment=0 >>> s.add(b, c) >>> print_mass_moment(b) mass=38 moment=75 >>> # Using Shape.mass >>> b = pymunk.Body() >>> c = pymunk.Circle(b, radius) >>> c.mass = mass >>> print_mass_moment(b) mass=0 moment=0 >>> s.add(b, c) >>> print_mass_moment(b) mass=3 moment=6 >>> # Using Body constructor >>> moment = pymunk.moment_for_circle(mass, 0, radius) >>> b = pymunk.Body() >>> c = pymunk.Circle(b, radius) >>> c.mass = mass >>> print_mass_moment(b) mass=0 moment=0 >>> s.add(b, c) >>> print_mass_moment(b) mass=3 moment=6 It becomes even more useful to use the mass or density properties of the shape when you attach multiple shapes to one body, like in this example with density: >>> # Using multiple Shape.density >>> b = pymunk.Body() >>> c1 = pymunk.Circle(b, radius, offset=(10,0)) >>> c1.density = density >>> c2 = pymunk.Circle(b, radius, offset=(0,10)) >>> c2.density = density >>> s.add(b, c1, c2) >>> print_mass_moment(b) mass=75 moment=3921 """ if body_type == Body.DYNAMIC: self._body = ffi.gc(cp.cpBodyNew(mass, moment), cp.cpBodyFree) elif body_type == Body.KINEMATIC: self._body = ffi.gc(cp.cpBodyNewKinematic(), cp.cpBodyFree) elif body_type == Body.STATIC: self._body = ffi.gc(cp.cpBodyNewStatic(), cp.cpBodyFree) self._init()
def _init(self): self._position_func = None # To prevent the gc to collect the callbacks. self._velocity_func = None # To prevent the gc to collect the callbacks. self._position_func_base = None # For pickle self._velocity_func_base = None # For pickle self._space = None # Weak ref to the space holding this body (if any) self._constraints = WeakSet() # weak refs to any constraints attached self._shapes = WeakSet() # weak refs to any shapes attached def __repr__(self): if self.body_type == Body.DYNAMIC: return 'Body(%r, %r, Body.DYNAMIC)' % (self.mass, self.moment) elif self.body_type == Body.KINEMATIC: return 'Body(Body.KINEMATIC)' elif self.body_type == Body.STATIC: return 'Body(Body.STATIC)' @classmethod def _init_with_body(cls, _body): """Only used internally in pymunk.""" b = cls.__new__(cls) b._body = _body b._init() return b def _set_mass(self, mass): cp.cpBodySetMass(self._body, mass) def _get_mass(self): return cp.cpBodyGetMass(self._body) mass = property(_get_mass, _set_mass, doc="""Mass of the body.""") def _set_moment(self, moment): cp.cpBodySetMoment(self._body, moment) def _get_moment(self): return cp.cpBodyGetMoment(self._body) moment = property(_get_moment, _set_moment, doc="""Moment of inertia (MoI or sometimes just moment) of the body. The moment is like the rotational mass of a body. """) def _set_position(self, pos): cp.cpBodySetPosition(self._body, tuple(pos)) def _get_position(self): p = cp.cpBodyGetPosition(self._body) return Vec2d._fromcffi(p) position = property(_get_position, _set_position, doc="""Position of the body. When changing the position you may also want to call :py:func:`Space.reindex_shapes_for_body` to update the collision detection information for the attached shapes if plan to make any queries against the space.""") def _set_center_of_gravity(self, cog): cp.cpBodySetCenterOfGravity(self._body, tuple(cog)) def _get_center_of_gravity(self): return Vec2d._fromcffi(cp.cpBodyGetCenterOfGravity(self._body)) center_of_gravity = property(_get_center_of_gravity, _set_center_of_gravity, doc="""Location of the center of gravity in body local coordinates. The default value is (0, 0), meaning the center of gravity is the same as the position of the body. """) def _set_velocity(self, vel): cp.cpBodySetVelocity(self._body, tuple(vel)) def _get_velocity(self): return Vec2d._fromcffi(cp.cpBodyGetVelocity(self._body)) velocity = property(_get_velocity, _set_velocity, doc="""Linear velocity of the center of gravity of the body.""") def _set_force(self, f): cp.cpBodySetForce(self._body, tuple(f)) def _get_force(self): return Vec2d._fromcffi(cp.cpBodyGetForce(self._body)) force = property(_get_force, _set_force, doc="""Force applied to the center of gravity of the body. This value is reset for every time step. Note that this is not the total of forces acting on the body (such as from collisions), but the force applied manually from the apply force functions.""") def _set_angle(self, angle): cp.cpBodySetAngle(self._body, angle) def _get_angle(self): return cp.cpBodyGetAngle(self._body) angle = property(_get_angle, _set_angle, doc="""Rotation of the body in radians. When changing the rotation you may also want to call :py:func:`Space.reindex_shapes_for_body` to update the collision detection information for the attached shapes if plan to make any queries against the space. A body rotates around its center of gravity, not its position. .. Note:: If you get small/no changes to the angle when for example a ball is "rolling" down a slope it might be because the Circle shape attached to the body or the slope shape does not have any friction set.""") def _set_angular_velocity(self, w): cp.cpBodySetAngularVelocity(self._body, w) def _get_angular_velocity(self): return cp.cpBodyGetAngularVelocity(self._body) angular_velocity = property(_get_angular_velocity, _set_angular_velocity, doc="""The angular velocity of the body in radians per second.""") def _set_torque(self, t): cp.cpBodySetTorque(self._body, t) def _get_torque(self): return cp.cpBodyGetTorque(self._body) torque = property(_get_torque, _set_torque, doc="""The torque applied to the body. This value is reset for every time step.""") def _get_rotation_vector(self): return Vec2d._fromcffi(cp.cpBodyGetRotation(self._body)) rotation_vector = property(_get_rotation_vector, doc="""The rotation vector for the body.""") def _get_space(self): if self._space != None: return self._space._get_self() #ugly hack because of weakref else: return None space = property(_get_space, doc="""Get the :py:class:`Space` that the body has been added to (or None).""") def _set_velocity_func(self, func): @ffi.callback("cpBodyVelocityFunc") def _impl(_, gravity, damping, dt): return func(self, Vec2d._fromcffi(gravity), damping, dt) self._velocity_func_base = func self._velocity_func = _impl cp.cpBodySetVelocityUpdateFunc(self._body, _impl) velocity_func = property(fset=_set_velocity_func, doc="""The velocity callback function. The velocity callback function is called each time step, and can be used to set a body's velocity. ``func(body : Body, gravity, damping, dt)`` There are many cases when this can be useful. One example is individual gravity for some bodies, and another is to limit the velocity which is useful to prevent tunneling. Example of a callback that sets gravity to zero for a object. >>> import pymunk >>> space = pymunk.Space() >>> space.gravity = 0, 10 >>> body = pymunk.Body(1,2) >>> space.add(body) >>> def zero_gravity(body, gravity, damping, dt): ... pymunk.Body.update_velocity(body, (0,0), damping, dt) ... >>> body.velocity_func = zero_gravity >>> space.step(1) >>> space.step(1) >>> print(body.position, body.velocity) Vec2d(0.0, 0.0) Vec2d(0.0, 0.0) Example of a callback that limits the velocity: >>> import pymunk >>> body = pymunk.Body(1,2) >>> def limit_velocity(body, gravity, damping, dt): ... max_velocity = 1000 ... pymunk.Body.update_velocity(body, gravity, damping, dt) ... l = body.velocity.length ... if l > max_velocity: ... scale = max_velocity / l ... body.velocity = body.velocity * scale ... >>> body.velocity_func = limit_velocity """) def _set_position_func(self, func): @ffi.callback("cpBodyPositionFunc") def _impl(_, dt): return func(self, dt) self._position_func_base = func self._position_func = _impl cp.cpBodySetPositionUpdateFunc(self._body, _impl) position_func = property(fset=_set_position_func, doc="""The position callback function. The position callback function is called each time step and can be used to update the body's position. ``func(body, dt) -> None`` """) def _get_kinetic_energy(self): #todo: use ffi method #return cp._cpBodyKineticEnergy(self._body) vsq = wsq = self.angular_velocity * self.angular_velocity return (vsq*self.mass if vsq else 0.) + (wsq*self.moment if wsq else 0.) kinetic_energy = property(_get_kinetic_energy, doc="""Get the kinetic energy of a body.""")
[docs] @staticmethod def update_velocity(body, gravity, damping, dt): """Default rigid body velocity integration function. Updates the velocity of the body using Euler integration. """ cp.cpBodyUpdateVelocity(body._body, tuple(gravity), damping, dt)
[docs] @staticmethod def update_position(body, dt): """Default rigid body position integration function. Updates the position of the body using Euler integration. Unlike the velocity function, it's unlikely you'll want to override this function. If you do, make sure you understand it's source code (in Chipmunk) as it's an important part of the collision/joint correction process. """ cp.cpBodyUpdatePosition(body._body, dt)
[docs] def apply_force_at_world_point(self, force, point): """Add the force force to body as if applied from the world point. People are sometimes confused by the difference between a force and an impulse. An impulse is a very large force applied over a very short period of time. Some examples are a ball hitting a wall or cannon firing. Chipmunk treats impulses as if they occur instantaneously by adding directly to the velocity of an object. Both impulses and forces are affected the mass of an object. Doubling the mass of the object will halve the effect. """ cp.cpBodyApplyForceAtWorldPoint(self._body, tuple(force), tuple(point))
[docs] def apply_force_at_local_point(self, force, point): """Add the local force force to body as if applied from the body local point. """ cp.cpBodyApplyForceAtLocalPoint(self._body, tuple(force), tuple(point))
[docs] def apply_impulse_at_world_point(self, impulse, point=(0, 0)): """Add the impulse impulse to body as if applied from the world point. """ cp.cpBodyApplyImpulseAtWorldPoint(self._body, tuple(impulse), tuple(point))
[docs] def apply_impulse_at_local_point(self, impulse, point=(0, 0)): """Add the local impulse impulse to body as if applied from the body local point. """ cp.cpBodyApplyImpulseAtLocalPoint(self._body, tuple(impulse), tuple(point))
[docs] def activate(self): """Reset the idle timer on a body. If it was sleeping, wake it and any other bodies it was touching. """ cp.cpBodyActivate(self._body)
[docs] def sleep(self): """Forces a body to fall asleep immediately even if it's in midair. Cannot be called from a callback. """ if self._space == None: raise Exception("Body not added to space") cp.cpBodySleep(self._body)
[docs] def sleep_with_group(self, body): """Force a body to fall asleep immediately along with other bodies in a group. When objects in Pymunk sleep, they sleep as a group of all objects that are touching or jointed together. When an object is woken up, all of the objects in its group are woken up. :py:func:`Body.sleep_with_group` allows you group sleeping objects together. It acts identically to :py:func:`Body.sleep` if you pass None as group by starting a new group. If you pass a sleeping body for group, body will be awoken when group is awoken. You can use this to initialize levels and start stacks of objects in a pre-sleeping state. """ if self._space == None: raise Exception("Body not added to space") cp.cpBodySleepWithGroup(self._body, body._body)
def _is_sleeping(self): return bool(cp.cpBodyIsSleeping(self._body)) is_sleeping = property(_is_sleeping, doc="""Returns true if the body is sleeping.""") def _set_type(self, body_type): cp.cpBodySetType(self._body, body_type) def _get_type(self): return cp.cpBodyGetType(self._body) body_type = property(_get_type , _set_type , doc="""The type of a body (:py:const:`Body.DYNAMIC`, :py:const:`Body.KINEMATIC` or :py:const:`Body.STATIC`). When changing an body to a dynamic body, the mass and moment of inertia are recalculated from the shapes added to the body. Custom calculated moments of inertia are not preserved when changing types. This function cannot be called directly in a collision callback. """)
[docs] def each_arbiter(self, func, *args, **kwargs): """Run func on each of the arbiters on this body. ``func(arbiter, *args, **kwargs) -> None`` Callback Parameters arbiter : :py:class:`Arbiter` The Arbiter args Optional parameters passed to the callback function. kwargs Optional keyword parameters passed on to the callback function. .. warning:: Do not hold on to the Arbiter after the callback! """ @ffi.callback("cpBodyArbiterIteratorFunc") def cf(_body, _arbiter, _data): arbiter = Arbiter(_arbiter, self._space) func(arbiter, *args, **kwargs) data = ffi.new_handle(self) cp.cpBodyEachArbiter(self._body, cf, data)
def _get_constraints(self): return set(self._constraints) constraints = property(_get_constraints, doc="""Get the constraints this body is attached to. The body only keeps a weak reference to the constraints and a live body wont prevent GC of the attached constraints""") def _get_shapes(self): return set(self._shapes) shapes = property(_get_shapes, doc="""Get the shapes attached to this body. The body only keeps a weak reference to the shapes and a live body wont prevent GC of the attached shapes""")
[docs] def local_to_world(self, v): """Convert body local coordinates to world space coordinates Many things are defined in coordinates local to a body meaning that the (0,0) is at the center of gravity of the body and the axis rotate along with the body. :param v: Vector in body local coordinates """ return Vec2d._fromcffi(cp.cpBodyLocalToWorld(self._body, tuple(v)))
[docs] def world_to_local(self, v): """Convert world space coordinates to body local coordinates :param v: Vector in world space coordinates """ return Vec2d._fromcffi(cp.cpBodyWorldToLocal(self._body, tuple(v)))
[docs] def velocity_at_world_point(self, point): """Get the absolute velocity of the rigid body at the given world point It's often useful to know the absolute velocity of a point on the surface of a body since the angular velocity affects everything except the center of gravity. """ return Vec2d._fromcffi( cp.cpBodyGetVelocityAtWorldPoint(self._body, tuple(point)))
[docs] def velocity_at_local_point(self, point): """ Get the absolute velocity of the rigid body at the given body local point """ return Vec2d._fromcffi( cp.cpBodyGetVelocityAtLocalPoint(self._body, tuple(point)))
def __getstate__(self): """Return the state of this object This method allows the usage of the :mod:`copy` and :mod:`pickle` modules with this class. """ d = super(Body, self).__getstate__() d['special'].append(('is_sleeping', self.is_sleeping)) d['special'].append(('_velocity_func', self._velocity_func_base)) d['special'].append(('_position_func', self._position_func_base)) return d def __setstate__(self, state): """Unpack this object from a saved state. This method allows the usage of the :mod:`copy` and :mod:`pickle` modules with this class. """ super(Body, self).__setstate__(state) for k,v in state['special']: if k == 'is_sleeping' and v: pass elif k == '_velocity_func' and v != None: self.velocity_func = v elif k == '_position_func' and v != None: self.position_func = v
[docs] def copy(self): """Create a deep copy of this body.""" return copy.deepcopy(self)