Math

Vector math types and functions. More...

Data Structures
struct	b2Vec2
	2D vector This can be used to represent a point or free vector More...
struct	b2CosSin
	Cosine and sine pair This uses a custom implementation designed for cross-platform determinism. More...
struct	b2Rot
	2D rotation This is similar to using a complex number for rotation More...
struct	b2Transform
	A 2D rigid transform. More...
struct	b2Mat22
	A 2-by-2 Matrix. More...
struct	b2AABB
	Axis-aligned bounding box. More...
struct	b2Plane
	separation = dot(normal, point) - offset More...

Macros
#define	B2_PI   3.14159265359f
	https://en.wikipedia.org/wiki/Pi

Typedefs
typedef b2Vec2	b2Pos
	Alias in single precision.
typedef b2Transform	b2WorldTransform
	Alias in single precision.

Functions
bool	b2IsValidFloat (float a)
	Is this a valid number? Not NaN or infinity.
bool	b2IsValidVec2 (b2Vec2 v)
	Is this a valid vector? Not NaN or infinity.
bool	b2IsValidRot (b2Rot q)
	Is this a valid rotation? Not NaN or infinity. Is normalized.
bool	b2IsValidTransform (b2Transform t)
	Is this a valid transform? Not NaN or infinity. Rotation is normalized.
bool	b2IsValidAABB (b2AABB aabb)
	Is this a valid bounding box?
bool	b2IsValidPlane (b2Plane a)
	Is this a valid plane? Normal is a unit vector. Not NaN or infinity.
bool	b2IsValidPos (b2Pos p)
	Is this a valid world position? Not NaN or infinity.
bool	b2IsValidWorldTransform (b2WorldTransform t)
	Is this a valid world transform? Not NaN or infinity. Rotation is normalized.
float	b2Atan2 (float y, float x)
	Compute an approximate arctangent in the range [-pi, pi] This is hand coded for cross-platform determinism.
b2CosSin	b2ComputeCosSin (float radians)
	Compute the cosine and sine of an angle in radians. Implemented for cross-platform determinism.
b2Rot	b2ComputeRotationBetweenUnitVectors (b2Vec2 v1, b2Vec2 v2)
	Compute the rotation between two unit vectors.
void	b2SetLengthUnitsPerMeter (float lengthUnits)
	Box2D bases all length units on meters, but you may need different units for your game.
float	b2GetLengthUnitsPerMeter (void)
	Get the current length units per meter.

Variables
BOX2D_EXPORT float	b2_lengthUnitsPerMeter
	This value is exported for efficiency. Don't modify directly.

Detailed Description

Vector math types and functions.

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Data Structure Documentation

b2Vec2

struct b2Vec2

2D vector This can be used to represent a point or free vector

Data Fields
float	x	coordinates
float	y

b2CosSin

struct b2CosSin

Cosine and sine pair This uses a custom implementation designed for cross-platform determinism.

Data Fields
float	cosine	cosine and sine
float	sine

b2Rot

struct b2Rot

2D rotation This is similar to using a complex number for rotation

Data Fields
float	c	cosine and sine
float	s

b2Transform

struct b2Transform

A 2D rigid transform.

Data Fields
b2Vec2	p
b2Rot	q

b2Mat22

struct b2Mat22

A 2-by-2 Matrix.

Data Fields
b2Vec2	cx	columns
b2Vec2	cy

b2AABB

struct b2AABB

Axis-aligned bounding box.

Data Fields
b2Vec2	lowerBound
b2Vec2	upperBound

b2Plane

struct b2Plane

separation = dot(normal, point) - offset

Data Fields
b2Vec2	normal
float	offset

Function Documentation

b2Atan2()

float b2Atan2	(	float	y,
		float	x )

Compute an approximate arctangent in the range [-pi, pi] This is hand coded for cross-platform determinism.

The atan2f function in the standard library is not cross-platform deterministic. Accurate to around 0.0023 degrees

b2IsValidAABB()

bool b2IsValidAABB

(

b2AABB

aabb

)

Is this a valid bounding box?

Not NaN or infinity. Upper bound greater than or equal to lower bound.

b2SetLengthUnitsPerMeter()

void b2SetLengthUnitsPerMeter

(

float

lengthUnits

)

Box2D bases all length units on meters, but you may need different units for your game.

You can set this value to use different units. This should be done at application startup and only modified once. Default value is 1. For example, if your game uses pixels for units you can use pixels for all length values sent to Box2D. There should be no extra cost. However, Box2D has some internal tolerances and thresholds that have been tuned for meters. By calling this function, Box2D is able to adjust those tolerances and thresholds to improve accuracy. A good rule of thumb is to pass the height of your player character to this function. So if your player character is 32 pixels high, then pass 32 to this function. Then you may confidently use pixels for all the length values sent to Box2D. All length values returned from Box2D will also be pixels because Box2D does not do any scaling internally. However, you are now on the hook for coming up with good values for gravity, density, and forces.

Warning

This must be modified before any calls to Box2D