Understanding the Light Orientation Issue in Three.js

Based on your code and description, it seems you're experiencing an issue with the orientation of your custom VolumetricSpotLight objects when using the lookAt() method. This is a common challenge when working with Three.js objects and their orientation.

The Problem

Your lights are positioned in a circle around an object, but when using lookAt(), they're not pointing exactly at the target as expected. The y-axis rotation appears to be off.

Potential Solutions

1. Check the Internal Structure of Your Custom Light

Your VolumetricSpotLight class returns a group of three elements. The issue might be related to how these elements are structured within the group:

• If your light's "forward" direction isn't aligned with the group's default forward direction (typically negative Z-axis in Three.js), the lookAt() method won't work as expected.

2. Use Helper Objects for Debugging

Consider using Three.js helpers to visualize the orientation:

JAVASCRIPTCopied
// Add an ArrowHelper to visualize the direction
const dir = new THREE.Vector3();
dir.subVectors(localPosition, light.position).normalize();
const arrowHelper = new THREE.ArrowHelper(dir, light.position, 5, 0x00ff00);
scene.add(arrowHelper);

3. Alternative Approach to Orientation

Instead of using lookAt(), you could try calculating the rotation directly:

JAVASCRIPTCopied
// Calculate direction vector from light to target
const direction = new THREE.Vector3();
direction.subVectors(localPosition, light.position).normalize();

// Convert direction to rotation (Euler angles)
const quaternion = new THREE.Quaternion();
quaternion.setFromUnitVectors(new THREE.Vector3(0, 0, -1), direction);
light.setRotationFromQuaternion(quaternion);

4. Check for Up Vector Issues

The lookAt() method uses an "up" vector (default is Y-up). If your custom light assumes a different up direction, this could cause the misalignment:

JAVASCRIPTCopied
// Try specifying a different up vector
const upVector = new THREE.Vector3(0, 1, 0);
light.lookAt(localPosition);
light.up.copy(upVector);
light.updateMatrix();

5. Reconsider Your Axis Inversion

Your current code inverts both X and Z rotations after lookAt():

JAVASCRIPTCopied
light.rotation.x *= -1;
light.rotation.z *= -1;

This suggests you're trying to compensate for an orientation issue. Instead of this approach, it might be better to fix the root cause. Try removing these lines and addressing the orientation within your VolumetricSpotLight class.

6. Check Child Object Orientations

If your light group contains child objects with their own orientations, those might need adjustment:

JAVASCRIPTCopied
// Adjust all children to face the same direction
light.children.forEach(child => {
    child.lookAt(localPosition);
});

Recommendation

1. First, use an AxesHelper to visualize the orientation of your light group:

JAVASCRIPTCopied
const axesHelper = new THREE.AxesHelper(5);
light.add(axesHelper);

2. Based on what you observe, adjust the internal structure of your VolumetricSpotLight class to ensure its "forward" direction aligns with Three.js's conventions.

3. If needed, consider adding a property to your light class that defines its forward direction, which you can use when applying rotations.

This approach should help you identify and fix the orientation issue with your lights.