Box3 for InstancedMesh

Questions
,
1

Hi,
I have an array of 3D Objects with different position, How can I create a bounding box with box3 for each object of my array?
I tried this but it doesn’t work

for (let i = 0; i < cubePoz.length; i++) {
  const cubeBox = new THREE.Box3().setFromArray(cubePoz[i]);
  const helper = new THREE.Box3Helper(cubeBox, 0xff0000);
  scene.add(helper);
}
2

Not sure the method you’re using is possible, likely best to generate a box3 from the original object and clone it for each instance setting them to the same transform as each matrix

3

You are setting the Box3 from your objects positions, which makes no sense. A single position cannot result in a volume of your mesh. Box3 is a helper class to generate a Boundingbox. Easiest way to set it is to use setFromObject(obj3D). Since you’re using instanceMesh, all objects have the same boundingbox, just at a different location.

4

How do I clone it? Can you introduce me an example or a reference?

5

ss
ss876×342 114 KB

How can I connect the location of box 3 to the instances?
Can you give me an example?

6

if you have an array of objects


let boxes = []

for(let o of objects) {

  let box = new THREE.Box3().setFromObject(o)
  boxes.push(box)
}

You could also make only one Box3 instance and reuse it

If you still wanna use instancedMesh instead, you can do something like this.


let instancedMesh = new THREE.InstancedMesh(geometry, material, amountOfInstances)
let box = new THREE.Box3().setFromObject(instancedMesh)

// set position of one instance for example
let matrix = new THREE.Matrix4().setPosition(10, 0, 15)
instancedMesh.setMatrixAt(index, matrix)
instancedMesh.instanceMatrix.needsUpdate = true

// Transform the boundingbox to the same position as your mesh instance
box.applyMatrix4(matrix)

// Get center
let center = new THREE.Vector3()
box.getCenter(center)
7

For each object in your array:
• clone the geometry of InstancedMesh,
• apply to it matrix of certain instance,
• create a new mesh with that geometry
and get the box form it.

for (let i = 0; i < instancedMesh.count; i++) {
 
  const instanceMatrix = new THREE.Matrix4();
  instancedMesh.getMatrixAt(i, instanceMatrix);
  
  const geo = instancedMesh.geometry.clone();
  geo.applyMatrix(instanceMatrix);

  const cubeBox = new THREE.Box3().setFromObject(new THREE.Mesh(geo));

  const helper = new THREE.Box3Helper(cubeBox, 0xff0000);
  scene.add(helper);
}