/*
* 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
#include
/// @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