Understanding the Geometry.center() and lookAt() Interaction

The issue you're experiencing with geometry.center() affecting the lookAt() behavior is related to how these two operations interact with the object's coordinate system.

The Problem

When you call geometry.center(), it modifies the geometry's vertices to center them around the origin (0,0,0) of the geometry's local coordinate system. This changes the internal structure of the geometry, which can affect how the object responds to transformations like lookAt().

The lookAt() method orients an object to face a specific point in world space, but it does this relative to the object's local coordinate system. When the geometry is centered, the local coordinate system's orientation might not align with what you expect.

Solution Approaches

Here are some approaches to solve this issue:

1. Apply geometry.center() before creating the mesh

Apply centering to the geometry before creating the mesh and applying any transformations:

JAVASCRIPTCopied
// Create and center the geometry first
const geometry = new THREE.BoxGeometry(width, height, depth);
geometry.center();

// Then create the mesh with the centered geometry
this.generatedShape = new THREE.Mesh(geometry, material);

// Now apply lookAt and other transformations
this.generatedShape.lookAt(targetPosition);

2. Use an Object3D as a parent container

Create a parent Object3D to handle the orientation, while the mesh with centered geometry remains a child:

JAVASCRIPTCopied
// Create and center the geometry
const geometry = new THREE.BoxGeometry(width, height, depth);
geometry.center();
const mesh = new THREE.Mesh(geometry, material);

// Create a parent container
this.generatedShape = new THREE.Object3D();
this.generatedShape.add(mesh);

// Apply lookAt to the parent
this.generatedShape.lookAt(targetPosition);

3. Adjust the pivot point instead of centering

Instead of using geometry.center(), you could adjust the mesh's position to achieve the same visual effect:

JAVASCRIPTCopied
const geometry = new THREE.BoxGeometry(width, height, depth);
const mesh = new THREE.Mesh(geometry, material);

// Calculate the center of the geometry
const center = new THREE.Vector3();
geometry.computeBoundingBox();
geometry.boundingBox.getCenter(center);

// Adjust the mesh position to compensate (instead of centering the geometry)
mesh.position.sub(center);

// Now lookAt should work as expected
mesh.lookAt(targetPosition);

4. Apply lookAt to a specific axis

If you need the object to look at a target along a specific axis, you might need to apply additional rotations:

JAVASCRIPTCopied
this.generatedShape.lookAt(targetPosition);
// Apply additional rotation to align a specific axis with the target
this.generatedShape.rotateOnAxis(new THREE.Vector3(1, 0, 0), Math.PI/2); // Example rotation

Remember that the order of operations matters in 3D transformations. Generally, it's best to:

1. Create and modify the geometry
2. Create the mesh
3. Apply position changes
4. Apply orientation/rotation changes

This sequence usually provides the most predictable results when working with Three.js objects.