Making Instanced Boxes Look at a Sphere in Three.js

To make instanced boxes orient toward a sphere's position in Three.js, you'll need to work with quaternions and matrices to handle the rotation of each instance. Here's how you can approach this:

Solution Overview

When using instanced meshes in Three.js, you need to set the transformation matrix for each instance. To make boxes look at a specific point, you'll need to:

1. Calculate the direction from each box to the sphere
2. Create a rotation quaternion based on this direction
3. Apply this rotation to the instance matrix

Implementation

Here's how you can implement this:

JAVASCRIPTCopied
// Assuming you have:
// - instancedBoxMesh (your InstancedMesh of boxes)
// - sphere (the target sphere that boxes should look at)
// - positions (array of Vector3 containing the position of each box)

const dummy = new THREE.Object3D();
const direction = new THREE.Vector3();

// For each instance
for (let i = 0; i < instancedBoxMesh.count; i++) {
  // Set the position
  dummy.position.copy(positions[i]);
  
  // Calculate direction from box to sphere
  direction.subVectors(sphere.position, positions[i]).normalize();
  
  // Make the dummy object look at the sphere
  dummy.lookAt(sphere.position);
  
  // Update the matrix for this instance
  dummy.updateMatrix();
  
  // Set the matrix of the instance
  instancedBoxMesh.setMatrixAt(i, dummy.matrix);
}

// Update the instance matrix buffer
instancedBoxMesh.instanceMatrix.needsUpdate = true;

Animation

If your sphere is moving and you want the boxes to continuously look at it, place this code in your animation loop:

JAVASCRIPTCopied
function animate() {
  requestAnimationFrame(animate);
  
  // Update box orientations
  for (let i = 0; i < instancedBoxMesh.count; i++) {
    dummy.position.copy(positions[i]);
    dummy.lookAt(sphere.position);
    dummy.updateMatrix();
    instancedBoxMesh.setMatrixAt(i, dummy.matrix);
  }
  
  instancedBoxMesh.instanceMatrix.needsUpdate = true;
  
  renderer.render(scene, camera);
}

This approach uses Three.js's built-in lookAt() method, which handles the quaternion calculations needed to orient objects toward a specific point in 3D space.