Body

This is the body API. More...

Data Structures
struct	b2MotionLocks
	Motion locks to restrict the body movement. More...
struct	b2BodyDef
	A body definition holds all the data needed to construct a rigid body. More...

Enumerations
enum	b2BodyType
	The body simulation type. More...

Functions
b2BodyId	b2CreateBody (b2WorldId worldId, const b2BodyDef *def)
	Create a rigid body given a definition.
void	b2DestroyBody (b2BodyId bodyId)
	Destroy a rigid body given an id.
bool	b2Body_IsValid (b2BodyId id)
	Body identifier validation.
b2BodyType	b2Body_GetType (b2BodyId bodyId)
	Get the body type: static, kinematic, or dynamic.
void	b2Body_SetType (b2BodyId bodyId, b2BodyType type)
	Change the body type.
void	b2Body_SetName (b2BodyId bodyId, const char *name)
	Set the body name. See B2_NAME_LENGTH.
const char *	b2Body_GetName (b2BodyId bodyId)
	Get the body name.
void	b2Body_SetUserData (b2BodyId bodyId, void *userData)
	Set the user data for a body.
void *	b2Body_GetUserData (b2BodyId bodyId)
	Get the user data stored in a body.
b2Pos	b2Body_GetPosition (b2BodyId bodyId)
	Get the world position of a body. This is the location of the body origin.
b2Rot	b2Body_GetRotation (b2BodyId bodyId)
	Get the world rotation of a body as a cosine/sine pair (complex number).
b2WorldTransform	b2Body_GetTransform (b2BodyId bodyId)
	Get the world transform of a body.
void	b2Body_SetTransform (b2BodyId bodyId, b2Pos position, b2Rot rotation)
	Set the world transform of a body.
b2Vec2	b2Body_GetLocalPoint (b2BodyId bodyId, b2Pos worldPoint)
	Get a local point on a body given a world point.
b2Pos	b2Body_GetWorldPoint (b2BodyId bodyId, b2Vec2 localPoint)
	Get a world point on a body given a local point.
b2Vec2	b2Body_GetLocalVector (b2BodyId bodyId, b2Vec2 worldVector)
	Get a local vector on a body given a world vector.
b2Vec2	b2Body_GetWorldVector (b2BodyId bodyId, b2Vec2 localVector)
	Get a world vector on a body given a local vector.
b2Vec2	b2Body_GetLinearVelocity (b2BodyId bodyId)
	Get the linear velocity of a body's center of mass. Usually in meters per second.
float	b2Body_GetAngularVelocity (b2BodyId bodyId)
	Get the angular velocity of a body in radians per second.
void	b2Body_SetLinearVelocity (b2BodyId bodyId, b2Vec2 linearVelocity)
	Set the linear velocity of a body. Usually in meters per second.
void	b2Body_SetAngularVelocity (b2BodyId bodyId, float angularVelocity)
	Set the angular velocity of a body in radians per second.
void	b2Body_SetTargetTransform (b2BodyId bodyId, b2WorldTransform target, float timeStep, bool wake)
	Set the velocity to reach the given transform after a given time step.
b2Vec2	b2Body_GetLocalPointVelocity (b2BodyId bodyId, b2Vec2 localPoint)
	Get the linear velocity of a local point attached to a body. Usually in meters per second.
b2Vec2	b2Body_GetWorldPointVelocity (b2BodyId bodyId, b2Pos worldPoint)
	Get the linear velocity of a world point attached to a body. Usually in meters per second.
void	b2Body_ApplyForce (b2BodyId bodyId, b2Vec2 force, b2Pos point, bool wake)
	Apply a force at a world point.
void	b2Body_ApplyForceToCenter (b2BodyId bodyId, b2Vec2 force, bool wake)
	Apply a force to the center of mass.
void	b2Body_ApplyTorque (b2BodyId bodyId, float torque, bool wake)
	Apply a torque.
void	b2Body_ClearForces (b2BodyId bodyId)
	Clear the force and torque on this body.
void	b2Body_ApplyLinearImpulse (b2BodyId bodyId, b2Vec2 impulse, b2Pos point, bool wake)
	Apply an impulse at a point.
void	b2Body_ApplyLinearImpulseToCenter (b2BodyId bodyId, b2Vec2 impulse, bool wake)
	Apply an impulse to the center of mass.
void	b2Body_ApplyAngularImpulse (b2BodyId bodyId, float impulse, bool wake)
	Apply an angular impulse.
float	b2Body_GetMass (b2BodyId bodyId)
	Get the mass of the body, usually in kilograms.
float	b2Body_GetRotationalInertia (b2BodyId bodyId)
	Get the rotational inertia of the body, usually in kg*m^2.
b2Vec2	b2Body_GetLocalCenter (b2BodyId bodyId)
	Get the center of mass position of the body in local space.
b2Pos	b2Body_GetWorldCenter (b2BodyId bodyId)
	Get the center of mass position of the body in world space.
void	b2Body_SetMassData (b2BodyId bodyId, b2MassData massData)
	Override the body's mass properties.
b2MassData	b2Body_GetMassData (b2BodyId bodyId)
	Get the mass data for a body.
void	b2Body_UpdateMassFromShapes (b2BodyId bodyId)
	This updates the mass properties to the sum of the mass properties of the shapes.
void	b2Body_SetLinearDamping (b2BodyId bodyId, float linearDamping)
	Adjust the linear damping. Normally this is set in b2BodyDef before creation.
float	b2Body_GetLinearDamping (b2BodyId bodyId)
	Get the current linear damping.
void	b2Body_SetAngularDamping (b2BodyId bodyId, float angularDamping)
	Adjust the angular damping. Normally this is set in b2BodyDef before creation.
float	b2Body_GetAngularDamping (b2BodyId bodyId)
	Get the current angular damping.
void	b2Body_SetGravityScale (b2BodyId bodyId, float gravityScale)
	Adjust the gravity scale.
float	b2Body_GetGravityScale (b2BodyId bodyId)
	Get the current gravity scale.
bool	b2Body_IsAwake (b2BodyId bodyId)
void	b2Body_SetAwake (b2BodyId bodyId, bool awake)
	Wake a body from sleep.
void	b2Body_WakeTouching (b2BodyId bodyId)
	Wake bodies touching this body. Works for static bodies.
void	b2Body_EnableSleeping (b2BodyId bodyId, bool enableSleep)
	Enable or disable sleeping for this body.
bool	b2Body_IsSleepingEnabled (b2BodyId bodyId)
	Returns true if sleeping is enabled for this body.
void	b2Body_SetSleepThreshold (b2BodyId bodyId, float sleepThreshold)
	Set the sleep threshold, usually in meters per second.
float	b2Body_GetSleepThreshold (b2BodyId bodyId)
	Get the sleep threshold, usually in meters per second.
void	b2Body_SetSafetyFactor (b2BodyId bodyId, float safetyFactor)
	Set the continuous collision safety factor.
float	b2Body_GetSafetyFactor (b2BodyId bodyId)
	Get the continuous collision safety factor. Non-dimensional.
bool	b2Body_IsEnabled (b2BodyId bodyId)
	Returns true if this body is enabled.
void	b2Body_Disable (b2BodyId bodyId)
	Disable a body by removing it completely from the simulation. This is expensive.
void	b2Body_Enable (b2BodyId bodyId)
	Enable a body by adding it to the simulation. This is expensive.
void	b2Body_SetMotionLocks (b2BodyId bodyId, b2MotionLocks locks)
	Set the motion locks on this body.
b2MotionLocks	b2Body_GetMotionLocks (b2BodyId bodyId)
	Get the motion locks for this body.
void	b2Body_SetBullet (b2BodyId bodyId, bool flag)
	Set this body to be a bullet.
bool	b2Body_IsBullet (b2BodyId bodyId)
	Is this body a bullet?
void	b2Body_EnableContactRecycling (b2BodyId bodyId, bool flag)
	Enable or disable contact recycling for this body.
bool	b2Body_IsContactRecyclingEnabled (b2BodyId bodyId)
	Is contact recycling enabled on this body?
void	b2Body_EnableContactEvents (b2BodyId bodyId, bool flag)
	Enable/disable contact events on all shapes.
void	b2Body_EnableHitEvents (b2BodyId bodyId, bool flag)
	Enable/disable hit events on all shapes.
b2WorldId	b2Body_GetWorld (b2BodyId bodyId)
	Get the world that owns this body.
int	b2Body_GetShapeCount (b2BodyId bodyId)
	Get the number of shapes on this body.
int	b2Body_GetShapes (b2BodyId bodyId, b2ShapeId *shapeArray, int capacity)
	Get the shape ids for all shapes on this body, up to the provided capacity.
int	b2Body_GetJointCount (b2BodyId bodyId)
	Get the number of joints on this body.
int	b2Body_GetJoints (b2BodyId bodyId, b2JointId *jointArray, int capacity)
	Get the joint ids for all joints on this body, up to the provided capacity.
int	b2Body_GetContactCapacity (b2BodyId bodyId)
	Get the maximum capacity required for retrieving all the touching contacts on a body.
int	b2Body_GetContactData (b2BodyId bodyId, b2ContactData *contactData, int capacity)
	Get the touching contact data for a body.
b2AABB	b2Body_ComputeBounds (b2BodyId bodyId)
	Get the current world AABB that contains all the attached shapes.
float	b2Body_GetMinExtent (b2BodyId bodyId)
	The minimum distance from any point on the body shapes to the center of mass.
float	b2Body_GetMaxExtent (b2BodyId bodyId)
	The maximum distance from any point on the body shapes to the center of mass.
float	b2Body_GetMaxExtentFromOrigin (b2BodyId bodyId)
	The maximum distance from any point on the body shapes to the body origin. Conservative.
b2BodyDef	b2DefaultBodyDef (void)
	Use this to initialize your body definition.

Detailed Description

This is the body API.

---

Data Structure Documentation

b2MotionLocks

struct b2MotionLocks

Motion locks to restrict the body movement.

Data Fields
bool	angularZ	Prevent rotation around the z-axis.
bool	linearX	Prevent translation along the x-axis.
bool	linearY	Prevent translation along the y-axis.

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().

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 used to slow down rotating bodies.
float	angularVelocity	The initial angular velocity of the body. Radians per second.
bool	enableContactRecycling	Enable contact recycling. True by default. Leaving this enabled improves performance but may lead to ghost collisions that should be avoided on characters.
bool	enableSleep	Set this flag to false if this body should never fall asleep.
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 dynamic body as a 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 do not guarantee accurate collision if both bodies are fast moving because the bullet does a continuous check after all non-bullet bodies have moved. You could get unlucky and have the bullet body end a time step very close to a non-bullet body and the non-bullet body then moves over the bullet body. In continuous collision, initial overlap is ignored to avoid freezing bodies in place. I do not recommend using them for game projectiles if precise collision timing is needed. Instead consider using a ray or shape cast. You can use a marching ray or shape cast for a projectile that moves over time. If you want a fast moving projectile to collide with a fast moving target, you need to consider the relative movement in your ray or shape cast. This is out of the scope of Box2D. So what are good use cases for bullets? Pinball games or games with dynamic containers that hold other objects. It should be a use case where it doesn't break the game if there is a collision missed, but having them captured improves the quality of the game.
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.
b2MotionLocks	motionLocks	Motion locks to restrict linear and angular movement. Caution: may lead to softer constraints along the locked direction
const char *	name	Optional body name for debugging. Up to B2_NAME_LENGTH characters.
b2Pos	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	safetyFactor	Continuous collision safety factor. The solver only uses continuous collision if there is a risk of tunneling. If the body is moving fast enough to risk tunneling then it is considered a "fast body". This improves performance and prevents movement hitches. If a body moving N meters risks tunneling, then the body will be considered fast if it moves more than a safetyFactor times N meters over one full time step. Non-dimensional. Recommended range [0.01, 0.5]. Default is 0.5 for high performance with low tunneling risk.
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()

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 torque, use a torque instead, which will work better with the sub-stepping solver.

b2Body_ApplyForce()

void b2Body_ApplyForce	(	b2BodyId	bodyId,
		b2Vec2	force,
		b2Pos	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()

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()

void b2Body_ApplyLinearImpulse	(	b2BodyId	bodyId,
		b2Vec2	impulse,
		b2Pos	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()

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_ApplyTorque()

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_ClearForces()

void b2Body_ClearForces

(

b2BodyId

bodyId

)

Clear the force and torque on this body.

Forces and torques are automatically cleared after each world step. So this only needs to be called if the application wants to remove the effect of previous calls to apply forces and torques before the world step is called.

Parameters

bodyId

The body id

b2Body_ComputeBounds()

b2AABB b2Body_ComputeBounds

(

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()

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_EnableContactRecycling()

void b2Body_EnableContactRecycling	(	b2BodyId	bodyId,
		bool	flag )

Enable or disable contact recycling for this body.

Contact recycling is a performance optimization that reuses contact manifolds when bodies move slightly. Disabling it can avoid ghost collisions on characters at the cost of higher per-step work. Existing contacts retain their prior setting; only contacts created after this call see the new value.

See also

b2BodyDef::enableContactRecycling

b2Body_EnableHitEvents()

void b2Body_EnableHitEvents	(	b2BodyId	bodyId,
		bool	flag )

Enable/disable hit events on all shapes.

See also

b2ShapeDef::enableHitEvents

b2Body_EnableSleeping()

void b2Body_EnableSleeping	(	b2BodyId	bodyId,
		bool	enableSleep )

Enable or disable sleeping for this body.

If sleeping is disabled the body will wake (and the entire island).

b2Body_GetContactData()

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()

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()

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()

bool b2Body_IsAwake

(

b2BodyId

bodyId

)

Returns

true if this body is awake

b2Body_IsValid()

bool b2Body_IsValid

(

b2BodyId

id

)

Body identifier validation.

A valid body exists in a world and is non-null. This can be used to detect orphaned ids. Provides validation for up to 64K allocations.

b2Body_SetAwake()

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()

void b2Body_SetBullet	(	b2BodyId	bodyId,
		bool	flag )

Set this body to be a bullet.

A bullet does continuous collision detection against dynamic and kinematic bodies (but not other bullets). This only works on dynamic bodies.

b2Body_SetGravityScale()

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()

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. If motion locks are used to fix rotation then the rotational inertia value is ignored and rotational inertia remains fixed at zero.

b2Body_SetMotionLocks()

void b2Body_SetMotionLocks	(	b2BodyId	bodyId,
		b2MotionLocks	locks )

Set the motion locks on this body.

This causes mass properties to be recomputed because fixed rotation sets the rotational inertia to zero.

b2Body_SetSafetyFactor()

void b2Body_SetSafetyFactor	(	b2BodyId	bodyId,
		float	safetyFactor )

Set the continuous collision safety factor.

Smaller is safer but can lead to hitching. Recommended range [0.01, 0.5]. Non-dimensional.

b2Body_SetTargetTransform()

void b2Body_SetTargetTransform	(	b2BodyId	bodyId,
		b2WorldTransform	target,
		float	timeStep,
		bool	wake )

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

The result will be close but may not be exact. This is meant for kinematic bodies. The target is not applied if the velocity would be below the sleep threshold and the body is currently asleep.

Parameters

bodyId	The body id
target	The target transform for the body
timeStep	The time step of the next call to b2World_Step
wake	Option to wake the body or not

b2Body_SetTransform()

void b2Body_SetTransform	(	b2BodyId	bodyId,
		b2Pos	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 the intended transform.

See also

b2BodyDef::position and b2BodyDef::rotation

b2Body_SetType()

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.

b2Body_UpdateMassFromShapes()

void b2Body_UpdateMassFromShapes

(

b2BodyId

bodyId

)

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

This normally does not need to be called unless you called b2Body_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.

b2CreateBody()

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()

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.