@gltf-transform/functions/src/center.ts

Functions for common glTF modifications, written using the core API

import type { Document, Transform, vec3 } from '@gltf-transform/core';
import { getBounds } from '@gltf-transform/core';
import { assignDefaults, createTransform } from './utils.js';

const NAME = 'center';

/** Options for the {@link center} function. */
export interface CenterOptions {
	/** Location on the model to be considered the pivot, and recentered at the origin. */
	pivot?: 'center' | 'above' | 'below' | vec3;
}

const CENTER_DEFAULTS: Required<CenterOptions> = { pivot: 'center' };

/**
 * Centers the {@link Scene} at the origin, or above/below it. Transformations from animation,
 * skinning, and morph targets are not taken into account.
 *
 * Example:
 *
 * ```ts
 * await document.transform(center({pivot: 'below'}));
 * ```
 *
 * @category Transforms
 */
export function center(_options: CenterOptions = CENTER_DEFAULTS): Transform {
	const options = assignDefaults(CENTER_DEFAULTS, _options);

	return createTransform(NAME, (doc: Document): void => {
		const logger = doc.getLogger();
		const root = doc.getRoot();
		const isAnimated = root.listAnimations().length > 0 || root.listSkins().length > 0;

		doc.getRoot()
			.listScenes()
			.forEach((scene, index) => {
				logger.debug(`${NAME}: Scene ${index + 1} / ${root.listScenes().length}.`);

				let pivot: vec3;
				if (typeof options.pivot === 'string') {
					const bbox = getBounds(scene);
					pivot = [
						(bbox.max[0] - bbox.min[0]) / 2 + bbox.min[0],
						(bbox.max[1] - bbox.min[1]) / 2 + bbox.min[1],
						(bbox.max[2] - bbox.min[2]) / 2 + bbox.min[2],
					];
					if (options.pivot === 'above') pivot[1] = bbox.max[1];
					if (options.pivot === 'below') pivot[1] = bbox.min[1];
				} else {
					pivot = options.pivot as vec3;
				}

				logger.debug(`${NAME}: Pivot "${pivot.join(', ')}".`);

				const offset: vec3 = [-1 * pivot[0], -1 * pivot[1], -1 * pivot[2]];

				if (isAnimated) {
					logger.debug(`${NAME}: Model contains animation or skin. Adding a wrapper node.`);
					const offsetNode = doc.createNode('Pivot').setTranslation(offset);
					scene.listChildren().forEach((child) => offsetNode.addChild(child));
					scene.addChild(offsetNode);
				} else {
					logger.debug(`${NAME}: Skipping wrapper, offsetting all root nodes.`);
					scene.listChildren().forEach((child) => {
						const t = child.getTranslation();
						child.setTranslation([t[0] + offset[0], t[1] + offset[1], t[2] + offset[2]]);
					});
				}
			});

		logger.debug(`${NAME}: Complete.`);
	});
}