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Workaround for sticky convex collisions when using GJK/EPA in combination with very small collision margins.

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In some degenerate cases the contact normal is pointing the wrong direction
so fix it now (until we can deal with all degenerate cases in GJK and EPA)
contact normals need to point from B to A in all cases, so we can simply check if the contact normal really points from B to A
We like to use a dot product of the normal against the difference of the centroids, 
once the centroid is available in the API
until then we use the center of the aabb to approximate the centroid
This commit is contained in:
erwin.coumans@gmail.com
2013-04-02 00:32:18 +00:00
parent 976cd0028a
commit 1f4f8c7e05
3 changed files with 27 additions and 4 deletions
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27
src/BulletCollision/NarrowPhaseCollision/btGjkPairDetector.cpp
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@@ -50,7 +50,8 @@ m_marginA(objectA->getMargin()),
m_marginB(objectB->getMargin()),
m_ignoreMargin(false),
m_lastUsedMethod(-1),
m_catchDegeneracies(1)
m_catchDegeneracies(1),
m_fixContactNormalDirection(1)
{
}
btGjkPairDetector::btGjkPairDetector(const btConvexShape* objectA,const btConvexShape* objectB,int shapeTypeA,int shapeTypeB,btScalar marginA, btScalar marginB, btSimplexSolverInterface* simplexSolver,btConvexPenetrationDepthSolver* penetrationDepthSolver)
@@ -65,7 +66,8 @@ m_marginA(marginA),
m_marginB(marginB),
m_ignoreMargin(false),
m_lastUsedMethod(-1),
m_catchDegeneracies(1)
m_catchDegeneracies(1),
m_fixContactNormalDirection(1)
{
}
@@ -438,6 +440,27 @@ void btGjkPairDetector::getClosestPointsNonVirtual(const ClosestPointInput& inpu
}
#endif
if (m_fixContactNormalDirection)
{
///@workaround for sticky convex collisions
//in some degenerate cases (usually when the use uses very small margins)
//the contact normal is pointing the wrong direction
//so fix it now (until we can deal with all degenerate cases in GJK and EPA)
//contact normals need to point from B to A in all cases, so we can simply check if the contact normal really points from B to A
//We like to use a dot product of the normal against the difference of the centroids,
//once the centroid is available in the API
//until then we use the center of the aabb to approximate the centroid
btVector3 aabbMin,aabbMax;
m_minkowskiA->getAabb(localTransA,aabbMin,aabbMax);
btVector3 posA = (aabbMax+aabbMin)*btScalar(0.5);
m_minkowskiB->getAabb(localTransB,aabbMin,aabbMax);
btVector3 posB = (aabbMin+aabbMax)*btScalar(0.5);
btVector3 diff = posA-posB;
if (diff.dot(normalInB) < 0.f)
normalInB *= -1.f;
}
m_cachedSeparatingAxis = normalInB;
m_cachedSeparatingDistance = distance;