btBvhTriangleMeshShape::partialRefitTree with smaller aabb?

[pico]

Hi,

i use "btBvhTriangleMeshShape::refitTree" to refit a changed triangle mesh. This works fine.
However, when using "btBvhTriangleMeshShape::partialRefitTree" i get an assertion for the new aaBBs.

The ASSERT code looks like its not allowed to refit a region that is smaller then the before region?!
Is this the case?

--------------------
void btOptimizedBvh::refitPartial(btStridingMeshInterface* meshInterface,const btVector3& aabbMin,const btVector3& aabbMax)
{
//incrementally initialize quantization values
btAssert(m_useQuantization);

btAssert(aabbMin.getX() > m_bvhAabbMin.getX());
btAssert(aabbMin.getY() > m_bvhAabbMin.getY());
btAssert(aabbMin.getZ() > m_bvhAabbMin.getZ());

btAssert(aabbMax.getX() < m_bvhAabbMax.getX());
btAssert(aabbMax.getY() < m_bvhAabbMax.getY());
btAssert(aabbMax.getZ() < m_bvhAabbMax.getZ());
--------------------

Thanks for your help

[Erwin Coumans]

The partial update requires an aabb that totally fits within the original full AABB of the triangle mesh. This means you have to provide a bigger AABB when creating the btBvhTriangleMeshShape, that encapsulated the total future deformation.

For example, say the mesh will deform 100 units maximum in the Y direction, then just add 10 units to the bvhAabbMin/bvhAabbMax during construction. It is safe to add some additional deformation extents, but keep it reasonable. Don't just add 100000 units, the trianglemesh/BVH performance will degrade dramatically due to lossy quantization. You can calculate the local aabb from the mesh using:

btVector3 bvhAabbMin,bvhAabbMax;
btVector3 additionalDeformationExtents(0,100,0);
meshInterface->calculateAabbBruteForce(bvhAabbMin,bvhAabbMax);
bvhAabbMin -= additionalDeformationExtents;
bvhAabbMax += additionalDeformationExtents

And make sure to use the right constructor, that passes in the bvhAabbMin/max:

btBvhTriangleMeshShape(btStridingMeshInterface* meshInterface, bool useQuantizedAabbCompression,const btVector3& bvhAabbMin,const btVector3& bvhAabbMax, bool buildBvh = true);

Hope this helps,
Erwin