/* Copyright (c) 2013 Scott Lembcke and Howling Moon Software
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/// @defgroup cpArbiter cpArbiter
/// The cpArbiter struct tracks pairs of colliding shapes.
/// They are also used in conjuction with collision handler callbacks
/// allowing you to retrieve information on the collision or change it.
/// A unique arbiter value is used for each pair of colliding objects. It persists until the shapes separate.
/// @{

#define CP_MAX_CONTACTS_PER_ARBITER 2

/// Get the restitution (elasticity) that will be applied to the pair of colliding objects.
CP_EXPORT cpFloat cpArbiterGetRestitution(const cpArbiter *arb);
/// Override the restitution (elasticity) that will be applied to the pair of colliding objects.
CP_EXPORT void cpArbiterSetRestitution(cpArbiter *arb, cpFloat restitution);
/// Get the friction coefficient that will be applied to the pair of colliding objects.
CP_EXPORT cpFloat cpArbiterGetFriction(const cpArbiter *arb);
/// Override the friction coefficient that will be applied to the pair of colliding objects.
CP_EXPORT void cpArbiterSetFriction(cpArbiter *arb, cpFloat friction);

// Get the relative surface velocity of the two shapes in contact.
CP_EXPORT cpVect cpArbiterGetSurfaceVelocity(cpArbiter *arb);

// Override the relative surface velocity of the two shapes in contact.
// By default this is calculated to be the difference of the two surface velocities clamped to the tangent plane.
CP_EXPORT void cpArbiterSetSurfaceVelocity(cpArbiter *arb, cpVect vr);

/// Get the user data pointer associated with this pair of colliding objects.
CP_EXPORT cpDataPointer cpArbiterGetUserData(const cpArbiter *arb);
/// Set a user data point associated with this pair of colliding objects.
/// If you need to perform any cleanup for this pointer, you must do it yourself, in the separate callback for instance.
CP_EXPORT void cpArbiterSetUserData(cpArbiter *arb, cpDataPointer userData);

/// Calculate the total impulse including the friction that was applied by this arbiter.
/// This function should only be called from a post-solve, post-step or cpBodyEachArbiter callback.
CP_EXPORT cpVect cpArbiterTotalImpulse(const cpArbiter *arb);
/// Calculate the amount of energy lost in a collision including static, but not dynamic friction.
/// This function should only be called from a post-solve, post-step or cpBodyEachArbiter callback.
CP_EXPORT cpFloat cpArbiterTotalKE(const cpArbiter *arb);

/// Mark a collision pair to be ignored until the two objects separate.
/// Pre-solve and post-solve callbacks will not be called, but the separate callback will be called.
CP_EXPORT cpBool cpArbiterIgnore(cpArbiter *arb);

/// Return the colliding shapes involved for this arbiter.
/// The order of their cpSpace.collision_type values will match
/// the order set when the collision handler was registered.
CP_EXPORT void cpArbiterGetShapes(const cpArbiter *arb, cpShape **a, cpShape **b);

/// A macro shortcut for defining and retrieving the shapes from an arbiter.
#define CP_ARBITER_GET_SHAPES(__arb__, __a__, __b__) cpShape *__a__, *__b__; cpArbiterGetShapes(__arb__, &__a__, &__b__);

/// Return the colliding bodies involved for this arbiter.
/// The order of the cpSpace.collision_type the bodies are associated with values will match
/// the order set when the collision handler was registered.
CP_EXPORT void cpArbiterGetBodies(const cpArbiter *arb, cpBody **a, cpBody **b);

/// A macro shortcut for defining and retrieving the bodies from an arbiter.
#define CP_ARBITER_GET_BODIES(__arb__, __a__, __b__) cpBody *__a__, *__b__; cpArbiterGetBodies(__arb__, &__a__, &__b__);

/// A struct that wraps up the important collision data for an arbiter.
struct cpContactPointSet {
	/// The number of contact points in the set.
	int count;
	
	/// The normal of the collision.
	cpVect normal;
	
	/// The array of contact points.
	struct {
		/// The position of the contact on the surface of each shape.
		cpVect pointA, pointB;
		/// Penetration distance of the two shapes. Overlapping means it will be negative.
		/// This value is calculated as cpvdot(cpvsub(point2, point1), normal) and is ignored by cpArbiterSetContactPointSet().
		cpFloat distance;
	} points[CP_MAX_CONTACTS_PER_ARBITER];
};

/// Return a contact set from an arbiter.
CP_EXPORT cpContactPointSet cpArbiterGetContactPointSet(const cpArbiter *arb);

/// Replace the contact point set for an arbiter.
/// This can be a very powerful feature, but use it with caution!
CP_EXPORT void cpArbiterSetContactPointSet(cpArbiter *arb, cpContactPointSet *set);

/// Returns true if this is the first step a pair of objects started colliding.
CP_EXPORT cpBool cpArbiterIsFirstContact(const cpArbiter *arb);
/// Returns true if the separate callback is due to a shape being removed from the space.
CP_EXPORT cpBool cpArbiterIsRemoval(const cpArbiter *arb);

/// Get the number of contact points for this arbiter.
CP_EXPORT int cpArbiterGetCount(const cpArbiter *arb);
/// Get the normal of the collision.
CP_EXPORT cpVect cpArbiterGetNormal(const cpArbiter *arb);
/// Get the position of the @c ith contact point on the surface of the first shape.
CP_EXPORT cpVect cpArbiterGetPointA(const cpArbiter *arb, int i);
/// Get the position of the @c ith contact point on the surface of the second shape.
CP_EXPORT cpVect cpArbiterGetPointB(const cpArbiter *arb, int i);
/// Get the depth of the @c ith contact point.
CP_EXPORT cpFloat cpArbiterGetDepth(const cpArbiter *arb, int i);

/// If you want a custom callback to invoke the wildcard callback for the first collision type, you must call this function explicitly.
/// You must decide how to handle the wildcard's return value since it may disagree with the other wildcard handler's return value or your own.
CP_EXPORT cpBool cpArbiterCallWildcardBeginA(cpArbiter *arb, cpSpace *space);
/// If you want a custom callback to invoke the wildcard callback for the second collision type, you must call this function explicitly.
/// You must decide how to handle the wildcard's return value since it may disagree with the other wildcard handler's return value or your own.
CP_EXPORT cpBool cpArbiterCallWildcardBeginB(cpArbiter *arb, cpSpace *space);

/// If you want a custom callback to invoke the wildcard callback for the first collision type, you must call this function explicitly.
/// You must decide how to handle the wildcard's return value since it may disagree with the other wildcard handler's return value or your own.
CP_EXPORT cpBool cpArbiterCallWildcardPreSolveA(cpArbiter *arb, cpSpace *space);
/// If you want a custom callback to invoke the wildcard callback for the second collision type, you must call this function explicitly.
/// You must decide how to handle the wildcard's return value since it may disagree with the other wildcard handler's return value or your own.
CP_EXPORT cpBool cpArbiterCallWildcardPreSolveB(cpArbiter *arb, cpSpace *space);

/// If you want a custom callback to invoke the wildcard callback for the first collision type, you must call this function explicitly.
CP_EXPORT void cpArbiterCallWildcardPostSolveA(cpArbiter *arb, cpSpace *space);
/// If you want a custom callback to invoke the wildcard callback for the second collision type, you must call this function explicitly.
CP_EXPORT void cpArbiterCallWildcardPostSolveB(cpArbiter *arb, cpSpace *space);

/// If you want a custom callback to invoke the wildcard callback for the first collision type, you must call this function explicitly.
CP_EXPORT void cpArbiterCallWildcardSeparateA(cpArbiter *arb, cpSpace *space);
/// If you want a custom callback to invoke the wildcard callback for the second collision type, you must call this function explicitly.
CP_EXPORT void cpArbiterCallWildcardSeparateB(cpArbiter *arb, cpSpace *space);

/// @}