278 lines
8.9 KiB
C
278 lines
8.9 KiB
C
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/*
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* Copyright (c) 2006-2009 Erin Catto http://www.box2d.org
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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#ifndef B2_COLLISION_H
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#define B2_COLLISION_H
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#include "Box2D/Common/b2Math.h"
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#include <limits.h>
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/// @file
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/// Structures and functions used for computing contact points, distance
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/// queries, and TOI queries.
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class b2Shape;
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class b2CircleShape;
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class b2EdgeShape;
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class b2PolygonShape;
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const uint8 b2_nullFeature = UCHAR_MAX;
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/// The features that intersect to form the contact point
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/// This must be 4 bytes or less.
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struct b2ContactFeature
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{
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enum Type
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{
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e_vertex = 0,
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e_face = 1
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};
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uint8 indexA; ///< Feature index on shapeA
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uint8 indexB; ///< Feature index on shapeB
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uint8 typeA; ///< The feature type on shapeA
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uint8 typeB; ///< The feature type on shapeB
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};
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/// Contact ids to facilitate warm starting.
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union b2ContactID
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{
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b2ContactFeature cf;
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uint32 key; ///< Used to quickly compare contact ids.
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};
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/// A manifold point is a contact point belonging to a contact
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/// manifold. It holds details related to the geometry and dynamics
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/// of the contact points.
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/// The local point usage depends on the manifold type:
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/// -e_circles: the local center of circleB
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/// -e_faceA: the local center of cirlceB or the clip point of polygonB
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/// -e_faceB: the clip point of polygonA
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/// This structure is stored across time steps, so we keep it small.
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/// Note: the impulses are used for internal caching and may not
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/// provide reliable contact forces, especially for high speed collisions.
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struct b2ManifoldPoint
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{
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b2Vec2 localPoint; ///< usage depends on manifold type
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float32 normalImpulse; ///< the non-penetration impulse
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float32 tangentImpulse; ///< the friction impulse
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b2ContactID id; ///< uniquely identifies a contact point between two shapes
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};
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/// A manifold for two touching convex shapes.
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/// Box2D supports multiple types of contact:
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/// - clip point versus plane with radius
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/// - point versus point with radius (circles)
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/// The local point usage depends on the manifold type:
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/// -e_circles: the local center of circleA
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/// -e_faceA: the center of faceA
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/// -e_faceB: the center of faceB
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/// Similarly the local normal usage:
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/// -e_circles: not used
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/// -e_faceA: the normal on polygonA
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/// -e_faceB: the normal on polygonB
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/// We store contacts in this way so that position correction can
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/// account for movement, which is critical for continuous physics.
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/// All contact scenarios must be expressed in one of these types.
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/// This structure is stored across time steps, so we keep it small.
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struct b2Manifold
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{
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enum Type
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{
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e_circles,
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e_faceA,
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e_faceB
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};
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b2ManifoldPoint points[b2_maxManifoldPoints]; ///< the points of contact
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b2Vec2 localNormal; ///< not use for Type::e_points
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b2Vec2 localPoint; ///< usage depends on manifold type
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Type type;
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int32 pointCount; ///< the number of manifold points
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};
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/// This is used to compute the current state of a contact manifold.
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struct b2WorldManifold
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{
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/// Evaluate the manifold with supplied transforms. This assumes
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/// modest motion from the original state. This does not change the
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/// point count, impulses, etc. The radii must come from the shapes
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/// that generated the manifold.
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void Initialize(const b2Manifold* manifold,
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const b2Transform& xfA, float32 radiusA,
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const b2Transform& xfB, float32 radiusB);
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b2Vec2 normal; ///< world vector pointing from A to B
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b2Vec2 points[b2_maxManifoldPoints]; ///< world contact point (point of intersection)
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float32 separations[b2_maxManifoldPoints]; ///< a negative value indicates overlap, in meters
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};
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/// This is used for determining the state of contact points.
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enum b2PointState
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{
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b2_nullState, ///< point does not exist
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b2_addState, ///< point was added in the update
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b2_persistState, ///< point persisted across the update
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b2_removeState ///< point was removed in the update
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};
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/// Compute the point states given two manifolds. The states pertain to the transition from manifold1
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/// to manifold2. So state1 is either persist or remove while state2 is either add or persist.
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void b2GetPointStates(b2PointState state1[b2_maxManifoldPoints], b2PointState state2[b2_maxManifoldPoints],
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const b2Manifold* manifold1, const b2Manifold* manifold2);
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/// Used for computing contact manifolds.
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struct b2ClipVertex
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{
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b2Vec2 v;
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b2ContactID id;
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};
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/// Ray-cast input data. The ray extends from p1 to p1 + maxFraction * (p2 - p1).
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struct b2RayCastInput
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{
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b2Vec2 p1, p2;
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float32 maxFraction;
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};
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/// Ray-cast output data. The ray hits at p1 + fraction * (p2 - p1), where p1 and p2
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/// come from b2RayCastInput.
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struct b2RayCastOutput
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{
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b2Vec2 normal;
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float32 fraction;
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};
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/// An axis aligned bounding box.
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struct b2AABB
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{
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/// Verify that the bounds are sorted.
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bool IsValid() const;
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/// Get the center of the AABB.
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b2Vec2 GetCenter() const
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{
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return 0.5f * (lowerBound + upperBound);
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}
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/// Get the extents of the AABB (half-widths).
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b2Vec2 GetExtents() const
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{
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return 0.5f * (upperBound - lowerBound);
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}
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/// Get the perimeter length
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float32 GetPerimeter() const
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{
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float32 wx = upperBound.x - lowerBound.x;
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float32 wy = upperBound.y - lowerBound.y;
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return 2.0f * (wx + wy);
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}
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/// Combine an AABB into this one.
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void Combine(const b2AABB& aabb)
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{
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lowerBound = b2Min(lowerBound, aabb.lowerBound);
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upperBound = b2Max(upperBound, aabb.upperBound);
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}
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/// Combine two AABBs into this one.
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void Combine(const b2AABB& aabb1, const b2AABB& aabb2)
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{
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lowerBound = b2Min(aabb1.lowerBound, aabb2.lowerBound);
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upperBound = b2Max(aabb1.upperBound, aabb2.upperBound);
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}
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/// Does this aabb contain the provided AABB.
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bool Contains(const b2AABB& aabb) const
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{
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bool result = true;
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result = result && lowerBound.x <= aabb.lowerBound.x;
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result = result && lowerBound.y <= aabb.lowerBound.y;
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result = result && aabb.upperBound.x <= upperBound.x;
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result = result && aabb.upperBound.y <= upperBound.y;
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return result;
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}
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bool RayCast(b2RayCastOutput* output, const b2RayCastInput& input) const;
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b2Vec2 lowerBound; ///< the lower vertex
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b2Vec2 upperBound; ///< the upper vertex
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};
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/// Compute the collision manifold between two circles.
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void b2CollideCircles(b2Manifold* manifold,
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const b2CircleShape* circleA, const b2Transform& xfA,
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const b2CircleShape* circleB, const b2Transform& xfB);
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/// Compute the collision manifold between a polygon and a circle.
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void b2CollidePolygonAndCircle(b2Manifold* manifold,
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const b2PolygonShape* polygonA, const b2Transform& xfA,
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const b2CircleShape* circleB, const b2Transform& xfB);
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/// Compute the collision manifold between two polygons.
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void b2CollidePolygons(b2Manifold* manifold,
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const b2PolygonShape* polygonA, const b2Transform& xfA,
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const b2PolygonShape* polygonB, const b2Transform& xfB);
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/// Compute the collision manifold between an edge and a circle.
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void b2CollideEdgeAndCircle(b2Manifold* manifold,
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const b2EdgeShape* polygonA, const b2Transform& xfA,
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const b2CircleShape* circleB, const b2Transform& xfB);
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/// Compute the collision manifold between an edge and a circle.
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void b2CollideEdgeAndPolygon(b2Manifold* manifold,
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const b2EdgeShape* edgeA, const b2Transform& xfA,
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const b2PolygonShape* circleB, const b2Transform& xfB);
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/// Clipping for contact manifolds.
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int32 b2ClipSegmentToLine(b2ClipVertex vOut[2], const b2ClipVertex vIn[2],
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const b2Vec2& normal, float32 offset, int32 vertexIndexA);
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/// Determine if two generic shapes overlap.
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bool b2TestOverlap( const b2Shape* shapeA, int32 indexA,
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const b2Shape* shapeB, int32 indexB,
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const b2Transform& xfA, const b2Transform& xfB);
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// ---------------- Inline Functions ------------------------------------------
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inline bool b2AABB::IsValid() const
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{
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b2Vec2 d = upperBound - lowerBound;
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bool valid = d.x >= 0.0f && d.y >= 0.0f;
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valid = valid && lowerBound.IsValid() && upperBound.IsValid();
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return valid;
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}
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inline bool b2TestOverlap(const b2AABB& a, const b2AABB& b)
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{
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b2Vec2 d1, d2;
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d1 = b.lowerBound - a.upperBound;
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d2 = a.lowerBound - b.upperBound;
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if (d1.x > 0.0f || d1.y > 0.0f)
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return false;
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if (d2.x > 0.0f || d2.y > 0.0f)
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return false;
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return true;
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}
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#endif
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