Body

This is the body API. More...

Data Structures
struct	b2BodyDef
	A body definition holds all the data needed to construct a rigid body. More...

Enumerations
enum	b2BodyType { b2_staticBody = 0 , b2_kinematicBody = 1 , b2_dynamicBody = 2 , b2_bodyTypeCount }
	The body simulation type. More...

Functions
B2_API b2BodyId	b2CreateBody (b2WorldId worldId, const b2BodyDef *def)
	Create a rigid body given a definition.
B2_API void	b2DestroyBody (b2BodyId bodyId)
	Destroy a rigid body given an id.
B2_API bool	b2Body_IsValid (b2BodyId id)
	Body identifier validation. Can be used to detect orphaned ids. Provides validation for up to 64K allocations.
B2_API b2BodyType	b2Body_GetType (b2BodyId bodyId)
	Get the body type: static, kinematic, or dynamic.
B2_API void	b2Body_SetType (b2BodyId bodyId, b2BodyType type)
	Change the body type.
B2_API void	b2Body_SetName (b2BodyId bodyId, const char *name)
	Set the body name. Up to 31 characters excluding 0 termination.
B2_API const char *	b2Body_GetName (b2BodyId bodyId)
	Get the body name. May be null.
B2_API void	b2Body_SetUserData (b2BodyId bodyId, void *userData)
	Set the user data for a body.
B2_API void *	b2Body_GetUserData (b2BodyId bodyId)
	Get the user data stored in a body.
B2_API b2Vec2	b2Body_GetPosition (b2BodyId bodyId)
	Get the world position of a body. This is the location of the body origin.
B2_API b2Rot	b2Body_GetRotation (b2BodyId bodyId)
	Get the world rotation of a body as a cosine/sine pair (complex number)
B2_API b2Transform	b2Body_GetTransform (b2BodyId bodyId)
	Get the world transform of a body.
B2_API void	b2Body_SetTransform (b2BodyId bodyId, b2Vec2 position, b2Rot rotation)
	Set the world transform of a body.
B2_API b2Vec2	b2Body_GetLocalPoint (b2BodyId bodyId, b2Vec2 worldPoint)
	Get a local point on a body given a world point.
B2_API b2Vec2	b2Body_GetWorldPoint (b2BodyId bodyId, b2Vec2 localPoint)
	Get a world point on a body given a local point.
B2_API b2Vec2	b2Body_GetLocalVector (b2BodyId bodyId, b2Vec2 worldVector)
	Get a local vector on a body given a world vector.
B2_API b2Vec2	b2Body_GetWorldVector (b2BodyId bodyId, b2Vec2 localVector)
	Get a world vector on a body given a local vector.
B2_API b2Vec2	b2Body_GetLinearVelocity (b2BodyId bodyId)
	Get the linear velocity of a body's center of mass. Usually in meters per second.
B2_API float	b2Body_GetAngularVelocity (b2BodyId bodyId)
	Get the angular velocity of a body in radians per second.
B2_API void	b2Body_SetLinearVelocity (b2BodyId bodyId, b2Vec2 linearVelocity)
	Set the linear velocity of a body. Usually in meters per second.
B2_API void	b2Body_SetAngularVelocity (b2BodyId bodyId, float angularVelocity)
	Set the angular velocity of a body in radians per second.
B2_API void	b2Body_SetTargetTransform (b2BodyId bodyId, b2Transform target, float timeStep)
	Set the velocity to reach the given transform after a given time step.
B2_API b2Vec2	b2Body_GetLocalPointVelocity (b2BodyId bodyId, b2Vec2 localPoint)
	Get the linear velocity of a local point attached to a body. Usually in meters per second.
B2_API b2Vec2	b2Body_GetWorldPointVelocity (b2BodyId bodyId, b2Vec2 worldPoint)
	Get the linear velocity of a world point attached to a body. Usually in meters per second.
B2_API void	b2Body_ApplyForce (b2BodyId bodyId, b2Vec2 force, b2Vec2 point, bool wake)
	Apply a force at a world point.
B2_API void	b2Body_ApplyForceToCenter (b2BodyId bodyId, b2Vec2 force, bool wake)
	Apply a force to the center of mass.
B2_API void	b2Body_ApplyTorque (b2BodyId bodyId, float torque, bool wake)
	Apply a torque.
B2_API void	b2Body_ApplyLinearImpulse (b2BodyId bodyId, b2Vec2 impulse, b2Vec2 point, bool wake)
	Apply an impulse at a point.
B2_API void	b2Body_ApplyLinearImpulseToCenter (b2BodyId bodyId, b2Vec2 impulse, bool wake)
	Apply an impulse to the center of mass.
B2_API void	b2Body_ApplyAngularImpulse (b2BodyId bodyId, float impulse, bool wake)
	Apply an angular impulse.
B2_API float	b2Body_GetMass (b2BodyId bodyId)
	Get the mass of the body, usually in kilograms.
B2_API float	b2Body_GetRotationalInertia (b2BodyId bodyId)
	Get the rotational inertia of the body, usually in kg*m^2.
B2_API b2Vec2	b2Body_GetLocalCenterOfMass (b2BodyId bodyId)
	Get the center of mass position of the body in local space.
B2_API b2Vec2	b2Body_GetWorldCenterOfMass (b2BodyId bodyId)
	Get the center of mass position of the body in world space.
B2_API void	b2Body_SetMassData (b2BodyId bodyId, b2MassData massData)
	Override the body's mass properties.
B2_API b2MassData	b2Body_GetMassData (b2BodyId bodyId)
	Get the mass data for a body.
B2_API void	b2Body_ApplyMassFromShapes (b2BodyId bodyId)
	This update the mass properties to the sum of the mass properties of the shapes.
B2_API void	b2Body_SetLinearDamping (b2BodyId bodyId, float linearDamping)
	Adjust the linear damping. Normally this is set in b2BodyDef before creation.
B2_API float	b2Body_GetLinearDamping (b2BodyId bodyId)
	Get the current linear damping.
B2_API void	b2Body_SetAngularDamping (b2BodyId bodyId, float angularDamping)
	Adjust the angular damping. Normally this is set in b2BodyDef before creation.
B2_API float	b2Body_GetAngularDamping (b2BodyId bodyId)
	Get the current angular damping.
B2_API void	b2Body_SetGravityScale (b2BodyId bodyId, float gravityScale)
	Adjust the gravity scale.
B2_API float	b2Body_GetGravityScale (b2BodyId bodyId)
	Get the current gravity scale.
B2_API bool	b2Body_IsAwake (b2BodyId bodyId)
B2_API void	b2Body_SetAwake (b2BodyId bodyId, bool awake)
	Wake a body from sleep.
B2_API void	b2Body_EnableSleep (b2BodyId bodyId, bool enableSleep)
	Enable or disable sleeping for this body. If sleeping is disabled the body will wake.
B2_API bool	b2Body_IsSleepEnabled (b2BodyId bodyId)
	Returns true if sleeping is enabled for this body.
B2_API void	b2Body_SetSleepThreshold (b2BodyId bodyId, float sleepThreshold)
	Set the sleep threshold, usually in meters per second.
B2_API float	b2Body_GetSleepThreshold (b2BodyId bodyId)
	Get the sleep threshold, usually in meters per second.
B2_API bool	b2Body_IsEnabled (b2BodyId bodyId)
	Returns true if this body is enabled.
B2_API void	b2Body_Disable (b2BodyId bodyId)
	Disable a body by removing it completely from the simulation. This is expensive.
B2_API void	b2Body_Enable (b2BodyId bodyId)
	Enable a body by adding it to the simulation. This is expensive.
B2_API void	b2Body_SetFixedRotation (b2BodyId bodyId, bool flag)
	Set this body to have fixed rotation. This causes the mass to be reset in all cases.
B2_API bool	b2Body_IsFixedRotation (b2BodyId bodyId)
	Does this body have fixed rotation?
B2_API void	b2Body_SetBullet (b2BodyId bodyId, bool flag)
	Set this body to be a bullet.
B2_API bool	b2Body_IsBullet (b2BodyId bodyId)
	Is this body a bullet?
B2_API void	b2Body_EnableContactEvents (b2BodyId bodyId, bool flag)
	Enable/disable contact events on all shapes.
B2_API void	b2Body_EnableHitEvents (b2BodyId bodyId, bool flag)
	Enable/disable hit events on all shapes.
B2_API b2WorldId	b2Body_GetWorld (b2BodyId bodyId)
	Get the world that owns this body.
B2_API int	b2Body_GetShapeCount (b2BodyId bodyId)
	Get the number of shapes on this body.
B2_API int	b2Body_GetShapes (b2BodyId bodyId, b2ShapeId *shapeArray, int capacity)
	Get the shape ids for all shapes on this body, up to the provided capacity.
B2_API int	b2Body_GetJointCount (b2BodyId bodyId)
	Get the number of joints on this body.
B2_API int	b2Body_GetJoints (b2BodyId bodyId, b2JointId *jointArray, int capacity)
	Get the joint ids for all joints on this body, up to the provided capacity.
B2_API int	b2Body_GetContactCapacity (b2BodyId bodyId)
	Get the maximum capacity required for retrieving all the touching contacts on a body.
B2_API int	b2Body_GetContactData (b2BodyId bodyId, b2ContactData *contactData, int capacity)
	Get the touching contact data for a body.
B2_API b2AABB	b2Body_ComputeAABB (b2BodyId bodyId)
	Get the current world AABB that contains all the attached shapes.
b2BodyDef	b2DefaultBodyDef (void)
	Use this to initialize your body definition.

Detailed Description

This is the body API.

---

Data Structure Documentation

b2BodyDef

struct b2BodyDef

A body definition holds all the data needed to construct a rigid body.

You can safely re-use body definitions. Shapes are added to a body after construction. Body definitions are temporary objects used to bundle creation parameters. Must be initialized using b2DefaultBodyDef().

Collaboration diagram for b2BodyDef:

Data Fields
bool	allowFastRotation	This allows this body to bypass rotational speed limits. Should only be used for circular objects, like wheels.
float	angularDamping	Angular damping is used to reduce the angular velocity. The damping parameter can be larger than 1.0f but the damping effect becomes sensitive to the time step when the damping parameter is large. Angular damping can be use slow down rotating bodies.
float	angularVelocity	The initial angular velocity of the body. Radians per second.
bool	enableSleep	Set this flag to false if this body should never fall asleep.
bool	fixedRotation	Should this body be prevented from rotating? Useful for characters.
float	gravityScale	Scale the gravity applied to this body. Non-dimensional.
int	internalValue	Used internally to detect a valid definition. DO NOT SET.
bool	isAwake	Is this body initially awake or sleeping?
bool	isBullet	Treat this body as high speed object that performs continuous collision detection against dynamic and kinematic bodies, but not other bullet bodies. Warning Bullets should be used sparingly. They are not a solution for general dynamic-versus-dynamic continuous collision. They may interfere with joint constraints.
bool	isEnabled	Used to disable a body. A disabled body does not move or collide.
float	linearDamping	Linear damping is used to reduce the linear velocity. The damping parameter can be larger than 1 but the damping effect becomes sensitive to the time step when the damping parameter is large. Generally linear damping is undesirable because it makes objects move slowly as if they are floating.
b2Vec2	linearVelocity	The initial linear velocity of the body's origin. Usually in meters per second.
const char *	name	Optional body name for debugging. Up to 31 characters (excluding null termination)
b2Vec2	position	The initial world position of the body. Bodies should be created with the desired position. Note Creating bodies at the origin and then moving them nearly doubles the cost of body creation, especially if the body is moved after shapes have been added.
b2Rot	rotation	The initial world rotation of the body. Use b2MakeRot() if you have an angle.
float	sleepThreshold	Sleep speed threshold, default is 0.05 meters per second.
b2BodyType	type	The body type: static, kinematic, or dynamic.
void *	userData	Use this to store application specific body data.

Enumeration Type Documentation

b2BodyType

enum b2BodyType

The body simulation type.

Each body is one of these three types. The type determines how the body behaves in the simulation.

Enumerator
b2_staticBody	zero mass, zero velocity, may be manually moved
b2_kinematicBody	zero mass, velocity set by user, moved by solver
b2_dynamicBody	positive mass, velocity determined by forces, moved by solver
b2_bodyTypeCount	number of body types

Function Documentation

b2Body_ApplyAngularImpulse()

B2_API void b2Body_ApplyAngularImpulse	(	b2BodyId	bodyId,
		float	impulse,
		bool	wake )

Apply an angular impulse.

The impulse is ignored if the body is not awake. This optionally wakes the body.

Parameters

bodyId	The body id
impulse	the angular impulse, usually in units of kg*m*m/s
wake	also wake up the body

Warning

This should be used for one-shot impulses. If you need a steady force, use a force instead, which will work better with the sub-stepping solver.

b2Body_ApplyForce()

B2_API void b2Body_ApplyForce	(	b2BodyId	bodyId,
		b2Vec2	force,
		b2Vec2	point,
		bool	wake )

Apply a force at a world point.

If the force is not applied at the center of mass, it will generate a torque and affect the angular velocity. This optionally wakes up the body. The force is ignored if the body is not awake.

Parameters

bodyId	The body id
force	The world force vector, usually in newtons (N)
point	The world position of the point of application
wake	Option to wake up the body

b2Body_ApplyForceToCenter()

B2_API void b2Body_ApplyForceToCenter	(	b2BodyId	bodyId,
		b2Vec2	force,
		bool	wake )

Apply a force to the center of mass.

This optionally wakes up the body. The force is ignored if the body is not awake.

Parameters

bodyId	The body id
force	the world force vector, usually in newtons (N).
wake	also wake up the body

b2Body_ApplyLinearImpulse()

B2_API void b2Body_ApplyLinearImpulse	(	b2BodyId	bodyId,
		b2Vec2	impulse,
		b2Vec2	point,
		bool	wake )

Apply an impulse at a point.

This immediately modifies the velocity. It also modifies the angular velocity if the point of application is not at the center of mass. This optionally wakes the body. The impulse is ignored if the body is not awake.

Parameters

bodyId	The body id
impulse	the world impulse vector, usually in N*s or kg*m/s.
point	the world position of the point of application.
wake	also wake up the body

Warning

This should be used for one-shot impulses. If you need a steady force, use a force instead, which will work better with the sub-stepping solver.

b2Body_ApplyLinearImpulseToCenter()

B2_API void b2Body_ApplyLinearImpulseToCenter	(	b2BodyId	bodyId,
		b2Vec2	impulse,
		bool	wake )

Apply an impulse to the center of mass.

This immediately modifies the velocity. The impulse is ignored if the body is not awake. This optionally wakes the body.

Parameters

bodyId	The body id
impulse	the world impulse vector, usually in N*s or kg*m/s.
wake	also wake up the body

Warning

This should be used for one-shot impulses. If you need a steady force, use a force instead, which will work better with the sub-stepping solver.

b2Body_ApplyMassFromShapes()

B2_API void b2Body_ApplyMassFromShapes

(

b2BodyId

bodyId

)

This update the mass properties to the sum of the mass properties of the shapes.

This normally does not need to be called unless you called SetMassData to override the mass and you later want to reset the mass. You may also use this when automatic mass computation has been disabled. You should call this regardless of body type. Note that sensor shapes may have mass.

b2Body_ApplyTorque()

B2_API void b2Body_ApplyTorque	(	b2BodyId	bodyId,
		float	torque,
		bool	wake )

Apply a torque.

This affects the angular velocity without affecting the linear velocity. This optionally wakes the body. The torque is ignored if the body is not awake.

Parameters

bodyId	The body id
torque	about the z-axis (out of the screen), usually in N*m.
wake	also wake up the body

b2Body_ComputeAABB()

B2_API b2AABB b2Body_ComputeAABB

(

b2BodyId

bodyId

)

Get the current world AABB that contains all the attached shapes.

Note that this may not encompass the body origin. If there are no shapes attached then the returned AABB is empty and centered on the body origin.

b2Body_EnableContactEvents()

B2_API void b2Body_EnableContactEvents	(	b2BodyId	bodyId,
		bool	flag )

Enable/disable contact events on all shapes.

See also

b2ShapeDef::enableContactEvents

Warning

changing this at runtime may cause mismatched begin/end touch events

b2Body_EnableHitEvents()

B2_API void b2Body_EnableHitEvents	(	b2BodyId	bodyId,
		bool	flag )

Enable/disable hit events on all shapes.

See also

b2ShapeDef::enableHitEvents

b2Body_GetContactData()

B2_API int b2Body_GetContactData	(	b2BodyId	bodyId,
		b2ContactData *	contactData,
		int	capacity )

Get the touching contact data for a body.

Note

Box2D uses speculative collision so some contact points may be separated.

Returns

the number of elements filled in the provided array

Warning

do not ignore the return value, it specifies the valid number of elements

b2Body_GetJoints()

B2_API int b2Body_GetJoints	(	b2BodyId	bodyId,
		b2JointId *	jointArray,
		int	capacity )

Get the joint ids for all joints on this body, up to the provided capacity.

Returns

the number of joint ids stored in the user array

b2Body_GetShapes()

B2_API int b2Body_GetShapes	(	b2BodyId	bodyId,
		b2ShapeId *	shapeArray,
		int	capacity )

Get the shape ids for all shapes on this body, up to the provided capacity.

Returns

the number of shape ids stored in the user array

b2Body_IsAwake()

B2_API bool b2Body_IsAwake

(

b2BodyId

bodyId

)

Returns

true if this body is awake

b2Body_SetAwake()

B2_API void b2Body_SetAwake	(	b2BodyId	bodyId,
		bool	awake )

Wake a body from sleep.

This wakes the entire island the body is touching.

Warning

Putting a body to sleep will put the entire island of bodies touching this body to sleep, which can be expensive and possibly unintuitive.

b2Body_SetBullet()

B2_API void b2Body_SetBullet	(	b2BodyId	bodyId,
		bool	flag )

Set this body to be a bullet.

A bullet does continuous collision detection against dynamic bodies (but not other bullets).

b2Body_SetGravityScale()

B2_API void b2Body_SetGravityScale	(	b2BodyId	bodyId,
		float	gravityScale )

Adjust the gravity scale.

Normally this is set in b2BodyDef before creation.

See also

b2BodyDef::gravityScale

b2Body_SetMassData()

B2_API void b2Body_SetMassData	(	b2BodyId	bodyId,
		b2MassData	massData )

Override the body's mass properties.

Normally this is computed automatically using the shape geometry and density. This information is lost if a shape is added or removed or if the body type changes.

b2Body_SetTargetTransform()

B2_API void b2Body_SetTargetTransform	(	b2BodyId	bodyId,
		b2Transform	target,
		float	timeStep )

Set the velocity to reach the given transform after a given time step.

The result will be close but maybe not exact. This is meant for kinematic bodies. This will automatically wake the body if asleep.

b2Body_SetTransform()

B2_API void b2Body_SetTransform	(	b2BodyId	bodyId,
		b2Vec2	position,
		b2Rot	rotation )

Set the world transform of a body.

This acts as a teleport and is fairly expensive.

Note

Generally you should create a body with then intended transform.

See also

b2BodyDef::position and b2BodyDef::angle

b2Body_SetType()

B2_API void b2Body_SetType	(	b2BodyId	bodyId,
		b2BodyType	type )

Change the body type.

This is an expensive operation. This automatically updates the mass properties regardless of the automatic mass setting.

b2CreateBody()

B2_API b2BodyId b2CreateBody	(	b2WorldId	worldId,
		const b2BodyDef *	def )

Create a rigid body given a definition.

No reference to the definition is retained. So you can create the definition on the stack and pass it as a pointer.

b2BodyDef bodyDef = b2DefaultBodyDef();
b2BodyId myBodyId = b2CreateBody(myWorldId, &bodyDef);

Warning

This function is locked during callbacks.

b2DestroyBody()

B2_API void b2DestroyBody

(

b2BodyId

bodyId

)

Destroy a rigid body given an id.

This destroys all shapes and joints attached to the body. Do not keep references to the associated shapes and joints.