deal with degenerate triangles in the btInternalEdgeUtility

thanks to scarrow, see http://bulletphysics.org/Bullet/phpBB3/viewtopic.php?f=9&t=4603&start=15

src/BulletCollision/CollisionDispatch/btInternalEdgeUtility.cpp

@@ -72,6 +72,17 @@ struct btConnectivityProcessor : public btTriangleCallback
 		int sharedVertsA[3]={-1,-1,-1};
 		int sharedVertsB[3]={-1,-1,-1};
 
+		///skip degenerate triangles
+		btScalar crossBSqr = ((triangle[1]-triangle[0]).cross(triangle[2]-triangle[0])).length2();
+		if (crossBSqr < m_triangleInfoMap->m_equalVertexThreshold)
+			return;
+
+
+		btScalar crossASqr = ((m_triangleVerticesA[1]-m_triangleVerticesA[0]).cross(m_triangleVerticesA[2]-m_triangleVerticesA[0])).length2();
+		///skip degenerate triangles
+		if (crossASqr< m_triangleInfoMap->m_equalVertexThreshold)
+			return;
+
 #if 0
 		printf("triangle A[0]	=	(%f,%f,%f)\ntriangle A[1]	=	(%f,%f,%f)\ntriangle A[2]	=	(%f,%f,%f)\n",
 			m_triangleVerticesA[0].getX(),m_triangleVerticesA[0].getY(),m_triangleVerticesA[0].getZ(),
@@ -94,8 +105,14 @@ struct btConnectivityProcessor : public btTriangleCallback
 					sharedVertsA[numshared] = i;
 					sharedVertsB[numshared] = j;
 					numshared++;
+					///degenerate case
+					if(numshared >= 3)
+						return;
 				}
 			}
+			///degenerate case
+			if(numshared >= 3)
+				return;
 		}
 		switch (numshared)
 		{

src/BulletCollision/CollisionDispatch/btInternalEdgeUtility.h

@@ -53,6 +53,8 @@ struct	btTriangleInfoMap : public btInternalTriangleInfoMap
 	btScalar	m_planarEpsilon; ///used to determine if a triangle edge is planar with zero angle
 	btScalar	m_equalVertexThreshold; ///used to compute connectivity: if the distance between two vertices is smaller than m_equalVertexThreshold, they are considered to be 'shared'
 	btScalar	m_edgeDistanceThreshold; ///used to determine edge contacts: if the closest distance between a contact point and an edge is smaller than this distance threshold it is considered to "hit the edge"
+	btScalar	m_zeroAreaThreshold; ///used to determine if a triangle is degenerate (length squared of cross product of 2 triangle edges < threshold)
+	
 	
 	btTriangleInfoMap()
 	{
@@ -60,6 +62,7 @@ struct	btTriangleInfoMap : public btInternalTriangleInfoMap
 		m_planarEpsilon = 0.0001f;
 		m_equalVertexThreshold = btScalar(0.0001)*btScalar(0.0001);
 		m_edgeDistanceThreshold = btScalar(0.1);
+		m_zeroAreaThreshold = btScalar(0.0001)*btScalar(0.0001);
 	}
 };