Physics.Hipmunk.Body

Rigid bodies and their properties.

Creating

data Body

A rigid body representing the physical properties of an object, but without a shape. It may help to think of it as a particle that is able to rotate.

Instances

Eq Body

Ord Body

Entity Body

newBody :: Mass -> Moment -> IO Body

newBody mass inertia creates a new Body with the given mass and moment of inertia.

It is recommended to call setPosition afterwards.

Static properties

Basic

Mass

type Mass = CpFloat

mass :: Body -> StateVar Mass

Moment of inertia

type Moment = CpFloat

moment :: Body -> StateVar Moment

Linear components of motion

Position

position :: Body -> StateVar Position

Note that using this function to change the position on every step is not recommended as it may leave the velocity out of sync.

Velocity

type Velocity = Vector

velocity :: Body -> StateVar Velocity

maxVelocity :: Body -> StateVar CpFloat

Maximum linear velocity after integrating, defaults to infinity.

Force

type Force = Vector

force :: Body -> StateVar Force

Angular components of motion

Angle

angle :: Body -> StateVar Angle

Angular velocity

type AngVel = CpFloat

angVel :: Body -> StateVar AngVel

maxAngVel :: Body -> StateVar CpFloat

Maximum angular velocity after integrating, defaults to infinity.

Torque

type Torque = CpFloat

torque :: Body -> StateVar Torque

Dynamic properties

slew :: Body -> Position -> Time -> IO ()

slew b newpos dt changes the body b's velocity so that it reaches newpos in dt time.

It is usually used to change the position of a static body in the world. In that case, remember to reset the velocity to zero afterwards!

updateVelocity :: Body -> Vector -> Damping -> Time -> IO ()

updateVelocity b gravity damping dt redefines body b's linear and angular velocity to account for the force/torque being applied to it, the gravity and a damping factor during dt time using Euler integration.

Note that this function only needs to be called if you are not adding the body to a space.

updatePosition :: Body -> Time -> IO ()

updatePosition b dt redefines the body position like updateVelocity (and it also shouldn't be called if you are adding this body to a space).

resetForces :: Body -> IO ()

resetForces b redefines as zero all forces and torque acting on body b.

applyForce :: Body -> Vector -> Position -> IO ()

applyForce b f r applies to the body b the force f with offset r, both vectors in world coordinates. This is the most stable way to change a body's velocity.

Note that the force is accumulated in the body, so you may need to call applyOnlyForce.

applyOnlyForce :: Body -> Vector -> Position -> IO ()

applyOnlyForce b f r applies a force like applyForce, but calling resetForces before. Note that using this function is preferable as it is optimized over this common case.

applyImpulse :: Body -> Vector -> Position -> IO ()

applyImpulse b j r applies to the body b the impulse j with offset r, both vectors in world coordinates.

applyDampedSpring :: (Body, Position) -> (Body, Position) -> Distance -> CpFloat -> Damping -> Time -> IO ()

dampedSpring (b1,a1) (b2,a2) rlen k dmp dt applies a damped spring force between bodies b1 and b2 at anchors a1 and a2, respectively. k is the spring constant (force/distance), rlen is the rest length of the spring, dmp is the damping constant (force/velocity), and dt is the time step to apply the force over. Both anchors are in body coordinates.

Note: large damping values can be unstable, you should use the damped spring constraint instead.

Utilities

localToWorld :: Body -> Position -> IO Position

For a vector p in body b's coordinates, localToWorld b p returns the corresponding vector in world coordinates.

worldToLocal :: Body -> Position -> IO Position

For a vector p in world coordinates, worldToLocal b p returns the corresponding vector in body b's coordinates.