Parents and Pivots

In Babylon.js, parents and pivots are crucial tools for creating complex, interactive 3D scenes by managing how multiple meshes relate to each other in terms of movement and transformation. These concepts enable developers to define hierarchical structures, where objects are connected in ways that mimic real-world relationships, allowing for more intuitive and efficient control over groups of objects.

Transform Node

A TransformNode is a special type of node used to organize and manage hierarchical transformations (position, rotation, scaling) within a 3D scene. Unlike meshes, a TransformNode does not have a visible geometry; its sole purpose is to control transformations for other objects, such as meshes, without rendering anything itself. This makes it an efficient way to manage complex transformations and parenting in a scene.

In the following example the transform node is rotating on Y-axis (both cubes are rotating around theirselves) and the red box is rotating on Z-axis.

const scene = useScene();
 
useEffect(() => {
    let angle = 0;
    function rotation() {
        transformNodeRef.current!.rotation.y = angle;
        boxRef.current!.rotation.z = angle;
        angle += 0.01;
    }
    scene.registerBeforeRender(rotation);
    return () => scene.unregisterBeforeRender(rotation);
}, []);
 
// ...
 
<transformNode ref={transformNodeRef} name='center-of-transformation'>
    <box ref={boxRef} name='box' positionZ={2}>
        <standardMaterial name='material' diffuseColor={Color3.Red()} />
    </box>
    <box name='small-box' position={new Vector3(0, 1, 0)} options={{ size: 0.5 }} />
</transformNode>

Parent

In the above example we used a parent to set the center of transformation for a mesh. Parenting establishes a direct relationship between two or more meshes, creating a parent-child hierarchy. When you parent one mesh to another, the child mesh becomes dependent on the parent mesh for transformations such as position, rotation, and scaling. This means that any movement, rotation, or scaling applied to the parent will automatically affect the child, but the child can still have its own local transformations relative to the parent. This hierarchical approach is powerful when building scenes where objects are naturally connected, such as:

• a robot where the limbs (arms, legs) are children of the body.
• a car where the wheels are children of the car’s body.
• a solar system where planets are children of the sun.

Pivot

The pivot point of a mesh is the point around which transformations (especially rotation and scaling) occur. By default, Babylon.js uses the mesh’s center as its pivot point, but this isn’t always ideal for every object or situation.

const scene = useScene();
 
useEffect(() => {
    new AxesViewer(scene, 3);
    let angle = 0;
    boxRef.current!.setPivotPoint(new Vector3(-1, -1, -1));
    function rotation() {
        boxRef.current!.rotation.y = angle;
        angle += 0.01;
    }
    scene.registerBeforeRender(rotation);
    return () => scene.unregisterBeforeRender(rotation);
}, []);
 
// ...
 
<>
    <box ref={boxRef} name='box' options={{ size: 2 }} position={new Vector3(-1,-1,-1)}>
        <standardMaterial name='box-material' wireframe />
        <sphere name='local-origin' options={{ diameter: 0.5 }} >
            <standardMaterial name='pivot-material' diffuseColor={Color3.Yellow()} />
        </sphere>
        <sphere name='pivot' options={{ diameter: 0.5 }} position={new Vector3(-1,-1,-1)}>
            <standardMaterial name='pivot-material' diffuseColor={Color3.Red()} />
        </sphere>
    </box>
</>

Moving the pivot point to a custom location allows you to control how and where the mesh rotates or scales, which is especially useful when building objects that need to rotate around a specific point, like:

• a door rotating around its hinge.
• a windmill blade spinning around its hub.
• a pendulum swinging from a fixed point.

Learn More

For properties and additional context, please refer to Babylon.js documentation: https://doc.babylonjs.com/features/featuresDeepDive/mesh/transforms/parent_pivot.