axmol/Box2D/Collision/b2Collision.h

/*
* Copyright (c) 2006-2009 Erin Catto http://www.gphysics.com
*
* This software is provided 'as-is', without any express or implied
* warranty.  In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/

#ifndef B2_COLLISION_H
#define B2_COLLISION_H

#include <Box2D/Common/b2Math.h>
#include <climits>

/// @file
/// Structures and functions used for computing contact points, distance
/// queries, and TOI queries.

class b2Shape;
class b2CircleShape;
class b2PolygonShape;

const uint8 b2_nullFeature = UCHAR_MAX;

/// Contact ids to facilitate warm starting.
union b2ContactID
{
	/// The features that intersect to form the contact point
	struct Features
	{
		uint8 referenceEdge;	///< The edge that defines the outward contact normal.
		uint8 incidentEdge;		///< The edge most anti-parallel to the reference edge.
		uint8 incidentVertex;	///< The vertex (0 or 1) on the incident edge that was clipped.
		uint8 flip;				///< A value of 1 indicates that the reference edge is on shape2.
	} features;
	uint32 key;					///< Used to quickly compare contact ids.
};

/// A manifold point is a contact point belonging to a contact
/// manifold. It holds details related to the geometry and dynamics
/// of the contact points.
/// The local point usage depends on the manifold type:
/// -e_circles: the local center of circleB
/// -e_faceA: the local center of cirlceB or the clip point of polygonB
/// -e_faceB: the clip point of polygonA
/// This structure is stored across time steps, so we keep it small.
/// Note: the impulses are used for internal caching and may not
/// provide reliable contact forces, especially for high speed collisions.
struct b2ManifoldPoint
{
	b2Vec2 localPoint;		///< usage depends on manifold type
	float32 normalImpulse;	///< the non-penetration impulse
	float32 tangentImpulse;	///< the friction impulse
	b2ContactID id;			///< uniquely identifies a contact point between two shapes
};

/// A manifold for two touching convex shapes.
/// Box2D supports multiple types of contact:
/// - clip point versus plane with radius
/// - point versus point with radius (circles)
/// The local point usage depends on the manifold type:
/// -e_circles: the local center of circleA
/// -e_faceA: the center of faceA
/// -e_faceB: the center of faceB
/// Similarly the local normal usage:
/// -e_circles: not used
/// -e_faceA: the normal on polygonA
/// -e_faceB: the normal on polygonB
/// We store contacts in this way so that position correction can
/// account for movement, which is critical for continuous physics.
/// All contact scenarios must be expressed in one of these types.
/// This structure is stored across time steps, so we keep it small.
struct b2Manifold
{
	enum Type
	{
		e_circles,
		e_faceA,
		e_faceB
	};

	b2ManifoldPoint points[b2_maxManifoldPoints];	///< the points of contact
	b2Vec2 localNormal;								///< not use for Type::e_points
	b2Vec2 localPoint;								///< usage depends on manifold type
	Type type;
	int32 pointCount;								///< the number of manifold points
};

/// This is used to compute the current state of a contact manifold.
struct b2WorldManifold
{
	/// Evaluate the manifold with supplied transforms. This assumes
	/// modest motion from the original state. This does not change the
	/// point count, impulses, etc. The radii must come from the shapes
	/// that generated the manifold.
	void Initialize(const b2Manifold* manifold,
					const b2Transform& xfA, float32 radiusA,
					const b2Transform& xfB, float32 radiusB);

	b2Vec2 normal;						///< world vector pointing from A to B
	b2Vec2 points[b2_maxManifoldPoints];	///< world contact point (point of intersection)
};

/// This is used for determining the state of contact points.
enum b2PointState
{
	b2_nullState,		///< point does not exist
	b2_addState,		///< point was added in the update
	b2_persistState,	///< point persisted across the update
	b2_removeState		///< point was removed in the update
};

/// Compute the point states given two manifolds. The states pertain to the transition from manifold1
/// to manifold2. So state1 is either persist or remove while state2 is either add or persist.
void b2GetPointStates(b2PointState state1[b2_maxManifoldPoints], b2PointState state2[b2_maxManifoldPoints],
					  const b2Manifold* manifold1, const b2Manifold* manifold2);

/// Used for computing contact manifolds.
struct b2ClipVertex
{
	b2Vec2 v;
	b2ContactID id;
};

/// Ray-cast input data. The ray extends from p1 to p1 + maxFraction * (p2 - p1).
struct b2RayCastInput
{
	b2Vec2 p1, p2;
	float32 maxFraction;
};

/// Ray-cast output data. The ray hits at p1 + fraction * (p2 - p1), where p1 and p2
/// come from b2RayCastInput.
struct b2RayCastOutput
{
	b2Vec2 normal;
	float32 fraction;
};

/// An axis aligned bounding box.
struct b2AABB
{
	/// Verify that the bounds are sorted.
	bool IsValid() const;

	/// Get the center of the AABB.
	b2Vec2 GetCenter() const
	{
		return 0.5f * (lowerBound + upperBound);
	}

	/// Get the extents of the AABB (half-widths).
	b2Vec2 GetExtents() const
	{
		return 0.5f * (upperBound - lowerBound);
	}

	/// Combine two AABBs into this one.
	void Combine(const b2AABB& aabb1, const b2AABB& aabb2)
	{
		lowerBound = b2Min(aabb1.lowerBound, aabb2.lowerBound);
		upperBound = b2Max(aabb1.upperBound, aabb2.upperBound);
	}

	/// Does this aabb contain the provided AABB.
	bool Contains(const b2AABB& aabb) const
	{
		bool result = true;
		result = result && lowerBound.x <= aabb.lowerBound.x;
		result = result && lowerBound.y <= aabb.lowerBound.y;
		result = result && aabb.upperBound.x <= upperBound.x;
		result = result && aabb.upperBound.y <= upperBound.y;
		return result;
	}

	bool RayCast(b2RayCastOutput* output, const b2RayCastInput& input) const;

	b2Vec2 lowerBound;	///< the lower vertex
	b2Vec2 upperBound;	///< the upper vertex
};

/// Compute the collision manifold between two circles.
void b2CollideCircles(b2Manifold* manifold,
					  const b2CircleShape* circle1, const b2Transform& xf1,
					  const b2CircleShape* circle2, const b2Transform& xf2);

/// Compute the collision manifold between a polygon and a circle.
void b2CollidePolygonAndCircle(b2Manifold* manifold,
							   const b2PolygonShape* polygon, const b2Transform& xf1,
							   const b2CircleShape* circle, const b2Transform& xf2);

/// Compute the collision manifold between two polygons.
void b2CollidePolygons(b2Manifold* manifold,
					   const b2PolygonShape* polygon1, const b2Transform& xf1,
					   const b2PolygonShape* polygon2, const b2Transform& xf2);

/// Clipping for contact manifolds.
int32 b2ClipSegmentToLine(b2ClipVertex vOut[2], const b2ClipVertex vIn[2],
							const b2Vec2& normal, float32 offset);

/// Determine if two generic shapes overlap.
bool b2TestOverlap(const b2Shape* shapeA, const b2Shape* shapeB,
				   const b2Transform& xfA, const b2Transform& xfB);

// ---------------- Inline Functions ------------------------------------------

inline bool b2AABB::IsValid() const
{
	b2Vec2 d = upperBound - lowerBound;
	bool valid = d.x >= 0.0f && d.y >= 0.0f;
	valid = valid && lowerBound.IsValid() && upperBound.IsValid();
	return valid;
}

inline bool b2TestOverlap(const b2AABB& a, const b2AABB& b)
{
	b2Vec2 d1, d2;
	d1 = b.lowerBound - a.upperBound;
	d2 = a.lowerBound - b.upperBound;

	if (d1.x > 0.0f || d1.y > 0.0f)
		return false;

	if (d2.x > 0.0f || d2.y > 0.0f)
		return false;

	return true;
}

#endif