Distance

Functions for computing the distance between shapes. More...

Data Structures
struct	b2SegmentDistanceResult
	Result of computing the distance between two line segments. More...
struct	b2DistanceProxy
	A distance proxy is used by the GJK algorithm. It encapsulates any shape. More...
struct	b2DistanceCache
	Used to warm start b2Distance. More...
struct	b2DistanceInput
	Input for b2ShapeDistance. More...
struct	b2DistanceOutput
	Output for b2ShapeDistance. More...
struct	b2SimplexVertex
	Simplex vertex for debugging the GJK algorithm. More...
struct	b2Simplex
	Simplex from the GJK algorithm. More...
struct	b2ShapeCastPairInput
	Input parameters for b2ShapeCast. More...
struct	b2Sweep
	This describes the motion of a body/shape for TOI computation. More...
struct	b2TOIInput
	Input parameters for b2TimeOfImpact. More...
struct	b2TOIOutput
	Output parameters for b2TimeOfImpact. More...

Enumerations
enum	b2TOIState {   b2_toiStateUnknown , b2_toiStateFailed , b2_toiStateOverlapped , b2_toiStateHit ,   b2_toiStateSeparated }
	Describes the TOI output.

Functions
b2SegmentDistanceResult	b2SegmentDistance (b2Vec2 p1, b2Vec2 q1, b2Vec2 p2, b2Vec2 q2)
	Compute the distance between two line segments, clamping at the end points if needed.
b2DistanceOutput	b2ShapeDistance (b2DistanceCache *cache, const b2DistanceInput *input, b2Simplex *simplexes, int simplexCapacity)
	Compute the closest points between two shapes represented as point clouds.
b2CastOutput	b2ShapeCast (const b2ShapeCastPairInput *input)
	Perform a linear shape cast of shape B moving and shape A fixed. Determines the hit point, normal, and translation fraction.
b2DistanceProxy	b2MakeProxy (const b2Vec2 *vertices, int32_t count, float radius)
	Make a proxy for use in GJK and related functions.
b2Transform	b2GetSweepTransform (const b2Sweep *sweep, float time)
	Evaluate the transform sweep at a specific time.
b2TOIOutput	b2TimeOfImpact (const b2TOIInput *input)
	Compute the upper bound on time before two shapes penetrate.

Detailed Description

Functions for computing the distance between shapes.

These are advanced functions you can use to perform distance calculations. There are functions for computing the closest points between shapes, doing linear shape casts, and doing rotational shape casts. The latter is called time of impact (TOI).

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Data Structure Documentation

b2SegmentDistanceResult

struct b2SegmentDistanceResult

Result of computing the distance between two line segments.

Collaboration diagram for b2SegmentDistanceResult:

Data Fields
b2Vec2	closest1	The closest point on the first segment.
b2Vec2	closest2	The closest point on the second segment.
float	distanceSquared	The squared distance between the closest points.
float	fraction1	The barycentric coordinate on the first segment.
float	fraction2	The barycentric coordinate on the second segment.

b2DistanceProxy

struct b2DistanceProxy

A distance proxy is used by the GJK algorithm. It encapsulates any shape.

Collaboration diagram for b2DistanceProxy:

Data Fields
int32_t	count	The number of points.
b2Vec2	points[b2_maxPolygonVertices]	The point cloud.
float	radius	The external radius of the point cloud.

b2DistanceCache

struct b2DistanceCache

Used to warm start b2Distance.

Set count to zero on first call or use zero initialization.

Data Fields
uint16_t	count	The number of stored simplex points.
uint8_t	indexA[3]	The cached simplex indices on shape A.
uint8_t	indexB[3]	The cached simplex indices on shape B.

b2DistanceInput

struct b2DistanceInput

Input for b2ShapeDistance.

Collaboration diagram for b2DistanceInput:

Data Fields
b2DistanceProxy	proxyA	The proxy for shape A.
b2DistanceProxy	proxyB	The proxy for shape B.
b2Transform	transformA	The world transform for shape A.
b2Transform	transformB	The world transform for shape B.
bool	useRadii	Should the proxy radius be considered?

b2DistanceOutput

struct b2DistanceOutput

Output for b2ShapeDistance.

Collaboration diagram for b2DistanceOutput:

Data Fields
float	distance	The final distance, zero if overlapped.
int32_t	iterations	Number of GJK iterations used.
b2Vec2	pointA	Closest point on shapeA.
b2Vec2	pointB	Closest point on shapeB.
int32_t	simplexCount	The number of simplexes stored in the simplex array.

b2SimplexVertex

struct b2SimplexVertex

Simplex vertex for debugging the GJK algorithm.

Collaboration diagram for b2SimplexVertex:

Data Fields
float	a	barycentric coordinate for closest point
int32_t	indexA	wA index
int32_t	indexB	wB index
b2Vec2	w	wB - wA
b2Vec2	wA	support point in proxyA
b2Vec2	wB	support point in proxyB

b2Simplex

struct b2Simplex

Simplex from the GJK algorithm.

Collaboration diagram for b2Simplex:

Data Fields
int32_t	count	number of valid vertices
b2SimplexVertex	v1
b2SimplexVertex	v2
b2SimplexVertex	v3	vertices

b2ShapeCastPairInput

struct b2ShapeCastPairInput

Input parameters for b2ShapeCast.

Collaboration diagram for b2ShapeCastPairInput:

Data Fields
float	maxFraction	The fraction of the translation to consider, typically 1.
b2DistanceProxy	proxyA	The proxy for shape A.
b2DistanceProxy	proxyB	The proxy for shape B.
b2Transform	transformA	The world transform for shape A.
b2Transform	transformB	The world transform for shape B.
b2Vec2	translationB	The translation of shape B.

b2Sweep

struct b2Sweep

This describes the motion of a body/shape for TOI computation.

Shapes are defined with respect to the body origin, which may not coincide with the center of mass. However, to support dynamics we must interpolate the center of mass position.

Collaboration diagram for b2Sweep:

Data Fields
b2Vec2	c1	Starting center of mass world position.
b2Vec2	c2	Ending center of mass world position.
b2Vec2	localCenter	Local center of mass position.
b2Rot	q1	Starting world rotation.
b2Rot	q2	Ending world rotation.

b2TOIInput

struct b2TOIInput

Input parameters for b2TimeOfImpact.

Collaboration diagram for b2TOIInput:

Data Fields
b2DistanceProxy	proxyA	The proxy for shape A.
b2DistanceProxy	proxyB	The proxy for shape B.
b2Sweep	sweepA	The movement of shape A.
b2Sweep	sweepB	The movement of shape B.
float	tMax	Defines the sweep interval [0, tMax].

b2TOIOutput

struct b2TOIOutput

Output parameters for b2TimeOfImpact.

Data Fields
b2TOIState	state	The type of result.
float	t	The time of the collision.

Function Documentation

b2ShapeDistance()

b2DistanceOutput b2ShapeDistance	(	b2DistanceCache *	cache,
		const b2DistanceInput *	input,
		b2Simplex *	simplexes,
		int	simplexCapacity )

Compute the closest points between two shapes represented as point clouds.

b2DistanceCache cache is input/output. On the first call set b2DistanceCache.count to zero. The underlying GJK algorithm may be debugged by passing in debug simplexes and capacity. You may pass in NULL and 0 for these.

b2TimeOfImpact()

b2TOIOutput b2TimeOfImpact

(

const b2TOIInput *

input

)

Compute the upper bound on time before two shapes penetrate.

Time is represented as a fraction between [0,tMax]. This uses a swept separating axis and may miss some intermediate, non-tunneling collisions. If you change the time interval, you should call this function again.