BatchedMesh how to do intersectsBox with three-mesh-bvh

[reef lily]

bvh installed like this https://github.com/gkjohnson/three-mesh-bvh?tab=readme-ov-file#use

then did

 for (const geometryUuid in geometries) {
      const geometry = geometries[geometryUuid]
      const geoId = batchedMesh.addGeometry(geometry)
      batchedMesh.computeBoundsTree(geoId)
    }

then placed all the instances to their respective locations

now i want to know if a box3 intersects with the entire batched mesh

i tried this but its always returning true

inverseMatrix.copy(batchedMesh.matrixWorld).invert()
for (let i = 0; i < batchedMesh.boundsTrees.length; i++) {
        if (batchedMesh.boundsTrees[i].intersectsBox(box3, inverseMatrix)) {
          hasIntersects = true
          break
        }
}

i also tried a version where instead of batched mesh the default mesh was used , using intersectsBox worked well in this case.

[reef lily]

@placid skiff 👋 ~hi !
is intersectsBox with a batched mesh an expected usecase ?

[placid skiff]

Individual sub-geometry BVHs can be accessed using the geometry id. The BVHs are stored in the local geometry frame so you need to pass the instance matrix into the functions:

for ( let i = 0; i < activeInstances.length; i ++ ) {

  const instanceId = activeInstances[ i ];
  const geometryId = batchedMesh.getGeometryIdAt( instanceId );
  const bvh = batchedMesh.boundsTrees( geometryId );
  batchedMesh.getMatrixAt( instanceId, _matrix );

  // construct transform from target frame into local geometry frame

  bvh.instsectsBox( box3, _localMatrix );

}

Perhaps @ripe remnant's wrappers have some more direct methods for this kind of functionality

[ripe remnant]

yes, with batchedmesh-extensions it's possible to compute a BVH that contains all instance, and use myBatchedMesh.bvh.intersectBox(myBox).

https://github.com/agargaro/batched-mesh-extensions/blob/master/src/core/BatchedMeshBVH.ts#L169

This checks if a bounding box (AABB) intersects one of more instances bounding box (always AABB).

This BVH is dynamic but can be really slow if you move all instances each frame.

const intersected = myBatchedMesh.bvh.intersectBox(myBox, ( instanceId ) => {
   // enter here if two bbox AABB collide
   // now we check if also geometry collides (using three-mesh-bvh)

  const geometryId = batchedMesh.getGeometryIdAt( instanceId );
  const bvh = batchedMesh.boundsTrees( geometryId );
  batchedMesh.getMatrixAt( instanceId, _matrix );
  
  // construct transform from target frame into local geometry frame

  return bvh.instsectsBox( box3, _localMatrix );
});

If it would be helpful I can prepare a small example

[reef lily]

when raycasting/boxIntersecting in a static scene :

1000 small normal meshes with each having bvh
vs
one batched mesh with 1000 instances with one bvh tree

would the performance difference be significant ? (assuming no rendering, so no draw call performance hit)

[ripe remnant]

should be the same