Real-Time Physics Simulation Forum

Topher wrote:I've recently added Bullet to our in-house engine but at present for shapes I've got everything using the same .bullet file I created with the serialiser. I'm curious what a typical or expected pipeline for artists to define the collision shape of a model would be for most people, or how I could make use of dynamica to help this.

Topher wrote: - Is dynamica's bullet export suppose to be used for defining the collision shapes of models, or is it purely for loading an entire bullet world?

Topher wrote: - Is there a way to instance shapes from a bullet file rather than just point to the data buffer of the file? For example if we want multiple instances of the same object using the same bullet file, however with different scale values on each instance of the shape. Is the only real solution to load the file into multiple separate buffers?

Topher wrote: - Why does the dynamica bullet export produce a world with lots of shapes and rigidy bodies? If I serialise my own shape for testing, I can serialise just a shape. Dynamica seems to export a lot more than just my current selection.

Erwin Coumans wrote: You should be able to export/serialize a single collision object with its shape into its own .bullet file.

Both should be possible. It is called: export all or export selection.

// Import shape
btBulletWorldImporter lImporter(0);
cScratchFile lFile( lpcCollisionFile );
mpBulletSerialisedData = (U8*)lpPartition->Alloc( lFile.GetSize() );
memcpy( mpBulletSerialisedData, lFile.GetBuffer(), lFile.GetSize() );

lImporter.loadFileFromMemory( (char*)mpBulletSerialisedData, lFile.GetSize() );
	
// Get imported shape
mpShape = new(lpPartition->Alloc( sizeof( btCompoundShape ) ) ) btCompoundShape();
for( S32 i = 0; i < lImporter.getNumRigidBodies(); ++i )
{
    btCollisionObject* lpRigidBody = lImporter.getRigidBodyByIndex(i);
    ASSERT(lpRigidBody);

    btCollisionShape* lpCollisionShape = lpRigidBody->getCollisionShape();
    ASSERT(lpCollisionShape);

    btTransform lLocalTransform = lpRigidBody->getWorldTransform();

    ((btCompoundShape*)mpShape)->addChildShape( lLocalTransform, lpCollisionShape );
}

// Define rigidbody and add the compound shape...

When you use the btBulletWorldImporter, it will create instances for btCollisionShape. You can instance and re-use those btCollisionShape as many times as you like.

Topher wrote: At the moment the only way I can see to do this is to de-serialise every time we use a bullet file associated with one of our entities. Ideally we'd like to only load unique files once and instance the shapes from this de-serialised data for performance. I can't think of a way to do this at the moment because I assume bullet shapes and compound shapes are all linked up via pointers and so on, not owning the data itself.

Am I going about this the wrong way?