Real-Time Physics Simulation Forum

Re: Can I make btTrangleMeshShape from btHeightfieldTerrainShape?

2022-02-19T03:42:12+00:00

Thanks for the answer!

I found this post : viewtopic.php?p=38852&hilit=btTriangleI ... ray#p38852

so I modify that codes like this :

Code:

class btTriangleCollector : public btTriangleCallback{public:std::vector* m_pVerticesOut;std::vector* m_pIndicesOut;btTriangleCollector(){m_pVerticesOut = NULL;m_pIndicesOut = NULL;}virtual void processTriangle(btVector3* tris, int partId, int triangleIndex){for (int k = 0; k < 3; k++){btVector3 v;for (int l = 0; l < 3; l++){v[l] = tris[k][l];}m_pIndicesOut->push_back(m_pVerticesOut->size());XMFLOAT3 vertex(v[0], v[1], v[2]);m_pVerticesOut->push_back(vertex);}}};auto TerrainShape = new btHeightfieldTerrainShape(mWidth * mTerrainScale.x, mDepth * mTerrainScale.z, mHeightmapData, minHeight, maxHeight, 1, false);TerrainShape->setLocalScaling(btVector3(1, mTerrainScale.y, 1));btVector3 aabbMin, aabbMax;for (int k = 0; k < 3; k++){aabbMin[k] = -BT_LARGE_FLOAT;aabbMax[k] = BT_LARGE_FLOAT;}std::vector vertices;std::vector Targetindices;btTriangleCollector collector;collector.m_pVerticesOut = &vertices;collector.m_pIndicesOut = &Targetindices;TerrainShape->processAllTriangles(&collector, aabbMin, aabbMax);mVertexArray = std::make_shared();btIndexedMesh tempMesh;mVertexArray->addIndexedMesh(tempMesh, PHY_FLOAT);btIndexedMesh& mesh = mVertexArray->getIndexedMeshArray()[0];const int32_t VERTICES_PER_TRIANGLE = 3;size_t numIndices = Targetindices.size();mesh.m_numTriangles = numIndices / VERTICES_PER_TRIANGLE;if (numIndices < std::numeric_limits::max()){mesh.m_triangleIndexBase = new unsigned char[sizeof(int16_t) * (size_t)numIndices];mesh.m_indexType = PHY_SHORT;mesh.m_triangleIndexStride = VERTICES_PER_TRIANGLE * sizeof(int16_t);}else{mesh.m_triangleIndexBase = new unsigned char[sizeof(int32_t) * (size_t)numIndices];mesh.m_indexType = PHY_INTEGER;mesh.m_triangleIndexStride = VERTICES_PER_TRIANGLE * sizeof(int32_t);}mesh.m_numVertices = vertices.size();mesh.m_vertexBase = new unsigned char[VERTICES_PER_TRIANGLE * sizeof(btScalar) * (size_t)mesh.m_numVertices];mesh.m_vertexStride = VERTICES_PER_TRIANGLE * sizeof(btScalar);btScalar* vertexData = static_cast((void*)(mesh.m_vertexBase));for (int32_t i = 0; i < mesh.m_numVertices; ++i){int32_t j = i * VERTICES_PER_TRIANGLE;const XMFLOAT3& point = vertices[i];vertexData[j] = point.x;vertexData[j + 1] = point.y;vertexData[j + 2] = point.z;}if (numIndices < std::numeric_limits::max()){int16_t* indices = static_cast((void*)(mesh.m_triangleIndexBase));for (int32_t i = 0; i < numIndices; ++i) {indices[i] = (int16_t)Targetindices[i];}}else{int32_t* indices = static_cast((void*)(mesh.m_triangleIndexBase));for (int32_t i = 0; i < numIndices; ++i) {indices[i] = Targetindices[i];}}btBvhTriangleMeshShape* shape = new btBvhTriangleMeshShape(mVertexArray.get(), true);btTransform btTerrainTransform;btTerrainTransform.setIdentity();btTerrainTransform.setOrigin(btVector3(0, 0, 0));mBtRigidBody = physics->CreateRigidBody(0.0f, btTerrainTransform, shape);

if this codes works well, mBtRigdBody's AABB must be min(-511.5, 4, -511.5), max(511.5, 242, 511.5)
but, actually what i got is min(-511.5, -105.389..., -511.5), max(511.5, 25.8... ,-500.5)

definitely wrong values.

I think btTriangleIndexVertexArray doesn't have right data of terrain, but, I can't find where's wrong.

Statistics: Posted by kcjsend2 — Sat Feb 19, 2022 3:42 am

Re: Can I make btTrangleMeshShape from btHeightfieldTerrainShape?

2022-02-18T16:10:30+00:00

Why does the vertexBase of the getLockedVertexIndexBase function receive double pointers?

The actual declaration for that API looks like this:

Code:

void getLockedVertexIndexBase(    unsigned char** vertexbase,    int& numverts,    PHY_ScalarType& type,    int& stride, unsigned char** indexbase,    int& indexstride,    int& numfaces,    PHY_ScalarType& indicestype,    int subpart = 0)

The API is: btStridingMeshInterface will cast a pointer to its own data to unsigned char* then set the supplied vertexbase to it, and also set type accordingly. All this so the receiving side can have the vertexbase pointer and cast back accordingly.

Unlike vector, btAlignedObjectArray does not have a data() function, so how do I get the location of the actual data?

There is btAlignedObjectArray::at(int n) (both const and non-const varieties) which returns the data by reference. You could probably snag the pointers from the references.

is this correct data?

Code:

m_pIndicesOut->push_back(m_pVerticesOut->size());

AFAICT the code is building its own triangle data which is a list of vertices (MyTriangleCollector3::m_pVerticesOut) and indices into that array of vertices (MyTriangleCollector3::m_pIndicesOut). So the index to the about-to-be-created vertex is the size of the array right before the vertex is added. It looks correct to me.

Statistics: Posted by drleviathan — Fri Feb 18, 2022 4:10 pm

Re: Can I make btTrangleMeshShape from btHeightfieldTerrainShape?

2022-02-18T07:14:00+00:00

I found it. threre's Demo named HeightFieldExample.

it collects all vertices and indices by TriangleCallback and processAllTriangles.

there's three more questions.

first, Why does the vertexBase of the getLockedVertexIndexBase function receive double pointers? The vertex information I have is in the form of btAlignedObjectArray, but I don't know how to pass it over to work well.

second, Unlike vector, btAlignedObjectArray does not have a data() function, so how do I get the location of the actual data?

third, actually in HeightFieldExample, btTriangleCallback collects indices by this code :

Code:

m_pIndicesOut->push_back(m_pVerticesOut->size());

is this correct data? I can't sure this data fits to btTriangleIndexVertexArray object.

Statistics: Posted by kcjsend2 — Fri Feb 18, 2022 7:14 am

Can I make btTriangleMeshShape from btHeightfieldTerrainShape?

2022-02-20T07:34:42+00:00

continues from this question : viewtopic.php?f=9&t=13374

hi.

I know these questions may seem a little short technically, but I don't know how to proceed, so I'm asking you this question.

We found that btStridingMeshInterface is required to create btBvhTriangleMeshShape.

But all I have is as much data as (Width * Height) for btTerrainHeightfieldShape. There is no index information on the data, so I don't know how to create a mesh in the Bullet.

Is there a simple way to change btTerrainHeightfieldShape to btBvhTriangleMeshShape? If there's no such way, how should I process my data?

Statistics: Posted by kcjsend2 — Fri Feb 18, 2022 4:43 am