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Medo Mex

Using D3DXComputeBoundingBox

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How do I use D3DXComputeBoundingBox() to calculate the box width/height/depth to create Bullet Physics btBoxShape?

 

I tried different ways but couldn't get it to work.

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D3DXVECTOR bMin, bMax;
BYTE* pData = 0;
mesh->LockVertexBuffer(0, (LPVOID*)&pData);
D3DXComputeBoundingBox((D3DXVECTOR3*)pData, mesh->GetNumVertices(),
            mesh->GetNumBytesPerVertex(), &bMin, &bMin);
mesh->UnlockVertexBuffer();
 
D3DXVECTOR3 boxHalfExtent = (bMax - bMin) * 0.5f;

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I tried your code after correcting the line:

D3DXComputeBoundingBox((D3DXVECTOR3*)pData, mesh->GetNumVertices(), mesh->GetNumBytesPerVertex(), &bMin, &bMin);

 

To:

D3DXComputeBoundingBox((D3DXVECTOR3*)pData, mesh->GetNumVertices(),mesh->GetNumBytesPerVertex(), &bMin, &bMax);

 

Now, the physical box appears to be larger than the actual mesh:

[attachment=15593:space.png]

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{
LPD3DXMESH mesh = GetMesh();

D3DXVECTOR3 bMin, bMax;
BYTE* pData = 0;
mesh->LockVertexBuffer(0, (LPVOID*)&pData);
D3DXComputeBoundingBox((D3DXVECTOR3*)pData, mesh->GetNumVertices(),
            mesh->GetNumBytesPerVertex(), &bMin, &bMax);
mesh->UnlockVertexBuffer();

D3DXVECTOR3 boxHalfExtent = (bMax - bMin) * 0.5f;
btVector3 btBoxHalfExtent(boxHalfExtent.x, boxHalfExtent.y, boxHalfExtent.z);

btBoxShape* boxShape = new btBoxShape(btBoxHalfExtent);

//keep track of the shapes, we release memory at exit.
//make sure to re-use collision shapes among rigid bodies whenever possible!
btAlignedObjectArray<btCollisionShape*> collisionShapes;

collisionShapes.push_back(boxShape);

btTransform trans;
trans.setIdentity();
trans.setOrigin(btVector3(0.0f, 0.0f, 0.0f));
btScalar mass(100.0f);

bool isDynamic = (mass != 0.f);

btVector3 localInertia(0,0,0);
if (isDynamic)
    boxShape->calculateLocalInertia(mass,localInertia);

// using motionstate is recommended, it provides interpolation capabilities, and only synchronizes 'active' objects
btDefaultMotionState* myMotionState = new btDefaultMotionState(trans);
btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,boxShape,localInertia);
btRigidBody* body = new btRigidBody(rbInfo);

// add the body to the dynamics world
mDynamicsWorld->addRigidBody(body);
}

 

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I noticed that I DON'T get this problem when I use D3DXCreateBox() for creating the box.

 

I only get this problem when I load the box mesh from .x file using D3DXLoadMeshFromX().

Edited by Medo3337

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Is your mesh centered at origin in modeling program?

If not you must then change btTransform origin, but i don't recommend this, better to fix this in modeling editor.

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Your box is working well.

 

Here is how I create my box, though it doesn't work:

[attachment=15610:mbox.png]

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