Physics.Hipmunk.Common

Functionality used by various modules and routines for initialization and change of global variables.

Initialization

initChipmunk :: IO ()

Initilizes the Chipmunk library. This should be called once before using any functions of this library.

Basic data types

type CpFloat = Double

The floating point type used internally in Chipmunk.

infinity :: CpFloat

infinity may be used to create bodies with an infinite mass.

type Time = CpFloat

Type synonym used to hint that the argument or result represents time.

type Angle = CpFloat

Type synonym used to hint that the argument or result represents an angle in radians.

type Distance = CpFloat

Type synonym used to hint that the argument or result represents a distance.

type Damping = CpFloat

Type synonym used to hint that the argument or result represents a damping constant.

Global variables

Chipmunk tries to maintain a very few number of global variables to allow multiple Spaces to be used simultaneously, however there are some.

Shape counter

The shape counter is a global counter used for creating unique hash identifiers to the shapes.

resetShapeCounter :: IO ()

resetShapeCounter reset the shape counter to its default value. This is used to add determinism to a simulation. As the ids created with this counter may affect the order in which the collisions happen, there may be very slight differences in different simulations. It may be very useful to call resetShapeCounter everytime you start a new simulation.

However, be careful as you should not use shapes created before a call to resetCounter with shapes created after it as they may have the same id. This means that you can't add shapes created after the call to a space created before it.

Contact persistence

This variable determines how long contacts should persist. It should be small as the cached contacts will only be close for a short time. (default is 3)

contactPersistence :: StateVar CInt

Collision slop

The collision slop is the amount that shapes are allowed to penetrate. Setting this to zero will work just fine, but using a small positive amount will help prevent oscillating contacts. (default is 0.1)

collisionSlop :: StateVar CpFloat

Bias coefficient

The amount of penetration to reduce in each step. Values should range from 0 to 1. Using large values will eliminate penetration in fewer steps, but can cause vibration. (default is 0.1)

type BiasCoef = CpFloat

biasCoef :: StateVar BiasCoef

Constraint bias coefficient

Similar to the bias coefficient, but sets the default bias for all constraints. (default is 0.1)

constraintBiasCoef :: StateVar BiasCoef

Vectors

data Vector

A two-dimensional vector. It is an instance of Num however the operations signum and (*) are not supported.

Constructors

Vector !CpFloat !CpFloat

Instances

Eq Vector

Num Vector

Ord Vector

Show Vector

Storable Vector

type Position = Vector

Type synonym used to hint that the argument or result represents a position.

fromAngle :: Angle -> Vector

Constructs an unitary vector pointing to the given angle (in radians).

len :: Vector -> CpFloat

The length of a vector.

normalize :: Vector -> Vector

Normalizes the vector (i.e. divides it by its length).

scale :: Vector -> CpFloat -> Vector

Scales the components of a vector by the same amount.

toAngle :: Vector -> Angle

toAngle v is the angle that v has with the vector Vector 1 0 (modulo 2*pi).

dot :: Vector -> Vector -> CpFloat

v1 `dot` v2 computes the familiar dot operation.

cross :: Vector -> Vector -> CpFloat

v1 `cross` v2 computes the familiar cross operation.

perp :: Vector -> Vector

perp v is a vector of same length as v but perpendicular to v (i.e. toAngle (perp v) - toAngle v equals pi/2 modulo 2*pi).

project :: Vector -> Vector -> Vector

v1 `project` v2 is the vector projection of v1 onto v2.

rotate :: Vector -> Vector -> Vector

v1 `rotate` v2 uses complex multiplication to rotate (and scale) v1 by v2.

unrotate :: Vector -> Vector -> Vector

The inverse operation of rotate, such that unrotate (rotate v1 v2) v2 equals v1.