b2Collision.h
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- /*
- * 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