BulletCollision/CollisionDispatch/btBox2dBox2dCollisionAlgorithm.cpp

/*
Bullet Continuous Collision Detection and Physics Library
* The b2CollidePolygons routines are Copyright (c) 2006-2007 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.
*/

///btBox2dBox2dCollisionAlgorithm, with modified b2CollidePolygons routines from the Box2D library.
///The modifications include: switching from b2Vec to btVector3, redefinition of b2Dot, b2Cross

#include "btBox2dBox2dCollisionAlgorithm.h"
#include "BulletCollision/CollisionDispatch/btCollisionDispatcher.h"
#include "BulletCollision/CollisionShapes/btBoxShape.h"
#include "BulletCollision/CollisionDispatch/btCollisionObject.h"
#include "BulletCollision/CollisionDispatch/btBoxBoxDetector.h"
#include "BulletCollision/CollisionShapes/btBox2dShape.h"
#include "BulletCollision/CollisionDispatch/btCollisionObjectWrapper.h"

#define USE_PERSISTENT_CONTACTS 1

btBox2dBox2dCollisionAlgorithm::btBox2dBox2dCollisionAlgorithm(btPersistentManifold* mf, const btCollisionAlgorithmConstructionInfo& ci, const btCollisionObjectWrapper* obj0Wrap, const btCollisionObjectWrapper* obj1Wrap)
	: btActivatingCollisionAlgorithm(ci, obj0Wrap, obj1Wrap),
	  m_ownManifold(false),
	  m_manifoldPtr(mf)
{
	if (!m_manifoldPtr && m_dispatcher->needsCollision(obj0Wrap->getCollisionObject(), obj1Wrap->getCollisionObject()))
	{
		m_manifoldPtr = m_dispatcher->getNewManifold(obj0Wrap->getCollisionObject(), obj1Wrap->getCollisionObject());
		m_ownManifold = true;
	}
}

btBox2dBox2dCollisionAlgorithm::~btBox2dBox2dCollisionAlgorithm()
{
	if (m_ownManifold)
	{
		if (m_manifoldPtr)
			m_dispatcher->releaseManifold(m_manifoldPtr);
	}
}

void b2CollidePolygons(btManifoldResult* manifold, const btBox2dShape* polyA, const btTransform& xfA, const btBox2dShape* polyB, const btTransform& xfB);

//#include <stdio.h>
void btBox2dBox2dCollisionAlgorithm::processCollision(const btCollisionObjectWrapper* body0Wrap, const btCollisionObjectWrapper* body1Wrap, const btDispatcherInfo& dispatchInfo, btManifoldResult* resultOut)
{
	if (!m_manifoldPtr)
		return;

	const btBox2dShape* box0 = (const btBox2dShape*)body0Wrap->getCollisionShape();
	const btBox2dShape* box1 = (const btBox2dShape*)body1Wrap->getCollisionShape();

	resultOut->setPersistentManifold(m_manifoldPtr);

	b2CollidePolygons(resultOut, box0, body0Wrap->getWorldTransform(), box1, body1Wrap->getWorldTransform());

	//  refreshContactPoints is only necessary when using persistent contact points. otherwise all points are newly added
	if (m_ownManifold)
	{
		resultOut->refreshContactPoints();
	}
}

btScalar btBox2dBox2dCollisionAlgorithm::calculateTimeOfImpact(btCollisionObject* /*body0*/, btCollisionObject* /*body1*/, const btDispatcherInfo& /*dispatchInfo*/, btManifoldResult* /*resultOut*/)
{
	//not yet
	return 1.f;
}

struct ClipVertex
{
	btVector3 v;
	int id;
	//b2ContactID id;
	//b2ContactID id;
};

#define b2Dot(a, b) (a).dot(b)
#define b2Mul(a, b) (a) * (b)
#define b2MulT(a, b) (a).transpose() * (b)
#define b2Cross(a, b) (a).cross(b)
#define btCrossS(a, s) btVector3(s* a.getY(), -s* a.getX(), 0.f)

int b2_maxManifoldPoints = 2;

static int ClipSegmentToLine(ClipVertex vOut[2], ClipVertex vIn[2],
							 const btVector3& normal, btScalar offset)
{
	// Start with no output points
	int numOut = 0;

	// Calculate the distance of end points to the line
	btScalar distance0 = b2Dot(normal, vIn[0].v) - offset;
	btScalar distance1 = b2Dot(normal, vIn[1].v) - offset;

	// If the points are behind the plane
	if (distance0 <= 0.0f) vOut[numOut++] = vIn[0];
	if (distance1 <= 0.0f) vOut[numOut++] = vIn[1];

	// If the points are on different sides of the plane
	if (distance0 * distance1 < 0.0f)
	{
		// Find intersection point of edge and plane
		btScalar interp = distance0 / (distance0 - distance1);
		vOut[numOut].v = vIn[0].v + interp * (vIn[1].v - vIn[0].v);
		if (distance0 > 0.0f)
		{
			vOut[numOut].id = vIn[0].id;
		}
		else
		{
			vOut[numOut].id = vIn[1].id;
		}
		++numOut;
	}

	return numOut;
}

// Find the separation between poly1 and poly2 for a give edge normal on poly1.
static btScalar EdgeSeparation(const btBox2dShape* poly1, const btTransform& xf1, int edge1,
							   const btBox2dShape* poly2, const btTransform& xf2)
{
	const btVector3* vertices1 = poly1->getVertices();
	const btVector3* normals1 = poly1->getNormals();

	int count2 = poly2->getVertexCount();
	const btVector3* vertices2 = poly2->getVertices();

	btAssert(0 <= edge1 && edge1 < poly1->getVertexCount());

	// Convert normal from poly1's frame into poly2's frame.
	btVector3 normal1World = b2Mul(xf1.getBasis(), normals1[edge1]);
	btVector3 normal1 = b2MulT(xf2.getBasis(), normal1World);

	// Find support vertex on poly2 for -normal.
	int index = 0;
	btScalar minDot = BT_LARGE_FLOAT;

	if (count2 > 0)
		index = (int)normal1.minDot(vertices2, count2, minDot);

	btVector3 v1 = b2Mul(xf1, vertices1[edge1]);
	btVector3 v2 = b2Mul(xf2, vertices2[index]);
	btScalar separation = b2Dot(v2 - v1, normal1World);
	return separation;
}

// Find the max separation between poly1 and poly2 using edge normals from poly1.
static btScalar FindMaxSeparation(int* edgeIndex,
								  const btBox2dShape* poly1, const btTransform& xf1,
								  const btBox2dShape* poly2, const btTransform& xf2)
{
	int count1 = poly1->getVertexCount();
	const btVector3* normals1 = poly1->getNormals();

	// Vector pointing from the centroid of poly1 to the centroid of poly2.
	btVector3 d = b2Mul(xf2, poly2->getCentroid()) - b2Mul(xf1, poly1->getCentroid());
	btVector3 dLocal1 = b2MulT(xf1.getBasis(), d);

	// Find edge normal on poly1 that has the largest projection onto d.
	int edge = 0;
	btScalar maxDot;
	if (count1 > 0)
		edge = (int)dLocal1.maxDot(normals1, count1, maxDot);

	// Get the separation for the edge normal.
	btScalar s = EdgeSeparation(poly1, xf1, edge, poly2, xf2);
	if (s > 0.0f)
	{
		return s;
	}

	// Check the separation for the previous edge normal.
	int prevEdge = edge - 1 >= 0 ? edge - 1 : count1 - 1;
	btScalar sPrev = EdgeSeparation(poly1, xf1, prevEdge, poly2, xf2);
	if (sPrev > 0.0f)
	{
		return sPrev;
	}

	// Check the separation for the next edge normal.
	int nextEdge = edge + 1 < count1 ? edge + 1 : 0;
	btScalar sNext = EdgeSeparation(poly1, xf1, nextEdge, poly2, xf2);
	if (sNext > 0.0f)
	{
		return sNext;
	}

	// Find the best edge and the search direction.
	int bestEdge;
	btScalar bestSeparation;
	int increment;
	if (sPrev > s && sPrev > sNext)
	{
		increment = -1;
		bestEdge = prevEdge;
		bestSeparation = sPrev;
	}
	else if (sNext > s)
	{
		increment = 1;
		bestEdge = nextEdge;
		bestSeparation = sNext;
	}
	else
	{
		*edgeIndex = edge;
		return s;
	}

	// Perform a local search for the best edge normal.
	for (;;)
	{
		if (increment == -1)
			edge = bestEdge - 1 >= 0 ? bestEdge - 1 : count1 - 1;
		else
			edge = bestEdge + 1 < count1 ? bestEdge + 1 : 0;

		s = EdgeSeparation(poly1, xf1, edge, poly2, xf2);
		if (s > 0.0f)
		{
			return s;
		}

		if (s > bestSeparation)
		{
			bestEdge = edge;
			bestSeparation = s;
		}
		else
		{
			break;
		}
	}

	*edgeIndex = bestEdge;
	return bestSeparation;
}

static void FindIncidentEdge(ClipVertex c[2],
							 const btBox2dShape* poly1, const btTransform& xf1, int edge1,
							 const btBox2dShape* poly2, const btTransform& xf2)
{
	const btVector3* normals1 = poly1->getNormals();

	int count2 = poly2->getVertexCount();
	const btVector3* vertices2 = poly2->getVertices();
	const btVector3* normals2 = poly2->getNormals();

	btAssert(0 <= edge1 && edge1 < poly1->getVertexCount());

	// Get the normal of the reference edge in poly2's frame.
	btVector3 normal1 = b2MulT(xf2.getBasis(), b2Mul(xf1.getBasis(), normals1[edge1]));

	// Find the incident edge on poly2.
	int index = 0;
	btScalar minDot = BT_LARGE_FLOAT;
	for (int i = 0; i < count2; ++i)
	{
		btScalar dot = b2Dot(normal1, normals2[i]);
		if (dot < minDot)
		{
			minDot = dot;
			index = i;
		}
	}

	// Build the clip vertices for the incident edge.
	int i1 = index;
	int i2 = i1 + 1 < count2 ? i1 + 1 : 0;

	c[0].v = b2Mul(xf2, vertices2[i1]);
	//	c[0].id.features.referenceEdge = (unsigned char)edge1;
	//	c[0].id.features.incidentEdge = (unsigned char)i1;
	//	c[0].id.features.incidentVertex = 0;

	c[1].v = b2Mul(xf2, vertices2[i2]);
	//	c[1].id.features.referenceEdge = (unsigned char)edge1;
	//	c[1].id.features.incidentEdge = (unsigned char)i2;
	//	c[1].id.features.incidentVertex = 1;
}

// Find edge normal of max separation on A - return if separating axis is found
// Find edge normal of max separation on B - return if separation axis is found
// Choose reference edge as min(minA, minB)
// Find incident edge
// Clip

// The normal points from 1 to 2
void b2CollidePolygons(btManifoldResult* manifold,
					   const btBox2dShape* polyA, const btTransform& xfA,
					   const btBox2dShape* polyB, const btTransform& xfB)
{
	int edgeA = 0;
	btScalar separationA = FindMaxSeparation(&edgeA, polyA, xfA, polyB, xfB);
	if (separationA > 0.0f)
		return;

	int edgeB = 0;
	btScalar separationB = FindMaxSeparation(&edgeB, polyB, xfB, polyA, xfA);
	if (separationB > 0.0f)
		return;

	const btBox2dShape* poly1;  // reference poly
	const btBox2dShape* poly2;  // incident poly
	btTransform xf1, xf2;
	int edge1;  // reference edge
	unsigned char flip;
	const btScalar k_relativeTol = 0.98f;
	const btScalar k_absoluteTol = 0.001f;

	// TODO_ERIN use "radius" of poly for absolute tolerance.
	if (separationB > k_relativeTol * separationA + k_absoluteTol)
	{
		poly1 = polyB;
		poly2 = polyA;
		xf1 = xfB;
		xf2 = xfA;
		edge1 = edgeB;
		flip = 1;
	}
	else
	{
		poly1 = polyA;
		poly2 = polyB;
		xf1 = xfA;
		xf2 = xfB;
		edge1 = edgeA;
		flip = 0;
	}

	ClipVertex incidentEdge[2];
	FindIncidentEdge(incidentEdge, poly1, xf1, edge1, poly2, xf2);

	int count1 = poly1->getVertexCount();
	const btVector3* vertices1 = poly1->getVertices();

	btVector3 v11 = vertices1[edge1];
	btVector3 v12 = edge1 + 1 < count1 ? vertices1[edge1 + 1] : vertices1[0];

	//btVector3 dv = v12 - v11;
	btVector3 sideNormal = b2Mul(xf1.getBasis(), v12 - v11);
	sideNormal.normalize();
	btVector3 frontNormal = btCrossS(sideNormal, 1.0f);

	v11 = b2Mul(xf1, v11);
	v12 = b2Mul(xf1, v12);

	btScalar frontOffset = b2Dot(frontNormal, v11);
	btScalar sideOffset1 = -b2Dot(sideNormal, v11);
	btScalar sideOffset2 = b2Dot(sideNormal, v12);

	// Clip incident edge against extruded edge1 side edges.
	ClipVertex clipPoints1[2];
	clipPoints1[0].v.setValue(0, 0, 0);
	clipPoints1[1].v.setValue(0, 0, 0);

	ClipVertex clipPoints2[2];
	clipPoints2[0].v.setValue(0, 0, 0);
	clipPoints2[1].v.setValue(0, 0, 0);

	int np;

	// Clip to box side 1
	np = ClipSegmentToLine(clipPoints1, incidentEdge, -sideNormal, sideOffset1);

	if (np < 2)
		return;

	// Clip to negative box side 1
	np = ClipSegmentToLine(clipPoints2, clipPoints1, sideNormal, sideOffset2);

	if (np < 2)
	{
		return;
	}

	// Now clipPoints2 contains the clipped points.
	btVector3 manifoldNormal = flip ? -frontNormal : frontNormal;

	int pointCount = 0;
	for (int i = 0; i < b2_maxManifoldPoints; ++i)
	{
		btScalar separation = b2Dot(frontNormal, clipPoints2[i].v) - frontOffset;

		if (separation <= 0.0f)
		{
			//b2ManifoldPoint* cp = manifold->points + pointCount;
			//btScalar separation = separation;
			//cp->localPoint1 = b2MulT(xfA, clipPoints2[i].v);
			//cp->localPoint2 = b2MulT(xfB, clipPoints2[i].v);

			manifold->addContactPoint(-manifoldNormal, clipPoints2[i].v, separation);

			//			cp->id = clipPoints2[i].id;
			//			cp->id.features.flip = flip;
			++pointCount;
		}
	}

	//	manifold->pointCount = pointCount;}
}