Description

Currently, BatchManager exposes methods like getGroupByName, but there is no public API to get a BatchGroup instance by its numeric id. This makes it inconvenient to work with batch groups when only the batchGroupId is available on components.

For example, components such as render, model or element store only batchGroupId, and there is no straightforward way to retrieve the corresponding BatchGroup object from the manager.

Proposal

Add a new method to BatchManager:

/**
 * Returns the BatchGroup with the specified id, or null if not found.
 * @param {number} id - The batch group id.
 * @returns {pc.BatchGroup|null}
 */
getGroupById(id) { ... }

This would mirror the existing getGroupByName API and provide a symmetric way to access batch groups either by name or by id.