@needle-tools/engine/src/engine-components/LookAtConstraint.ts

Needle Engine is a web-based runtime for 3D apps. It runs on your machine for development with great integrations into editors like Unity or Blender - and can be deployed onto any device! It is flexible, extensible and networking and XR are built-in.

import { Object3D, Vector3 } from "three";

import { serializable } from "../engine/engine_serialization_decorator.js";
import type { LookAt } from "./api.js";
import { Behaviour } from "./Component.js";
import type { OrbitControls } from "./OrbitControls.js";

/**
 * The [LookAtConstraint](https://engine.needle.tools/docs/api/LookAtConstraint) component is primarely used by {@link OrbitControls} to set the camera's focus point.
 * It does not have its own logic to update the look-at position.  
 *
 * The constraint uses a list of source objects - the look-at target is  
 * calculated from the first source in the `sources` array.  
 *
 * **Integration with OrbitControls:**  
 * When attached to the same GameObject as OrbitControls, this constraint  
 * controls where the camera orbits around and looks at.  
 *
 * @summary Look At Constraint for camera targeting
 * @category Camera and Controls
 * @group Components
 * @see {@link OrbitControls} for camera orbit controls
 * @see {@link SmoothFollow} for smooth position/rotation following
 * @see {@link LookAt} for directly making an object look at a target without using a constraint
 */
export class LookAtConstraint extends Behaviour {

    /**
     * When true, the constraint is active and affects the target.
     * Set to false to temporarily disable without removing sources.
     */
    @serializable()
    constraintActive: boolean = true;

    /**
     * When true, the look-at position is locked and won't update
     * even if source objects move.
     */
    @serializable()
    locked: boolean = false;

    /**
     * Objects to look at. The first object in the array is used
     * as the primary look-at target.
     */
    @serializable(Object3D)
    sources: Object3D[] = [];

    /**
     * Sets the world position that the constraint should look at.
     * Updates the first source object's position.
     * @param worldPosition The world-space position to look at
     */
    setConstraintPosition(worldPosition: Vector3) {
        const source = this.sources[0];
        if (source) source.worldPosition = worldPosition;
    }
}