interaction-groups.ts

import { InteractionGroups } from "@dimforge/rapier3d-compat";

/**
 * Calculates an InteractionGroup bitmask for use in the `collisionGroups` or `solverGroups`
 * properties of RigidBody or Collider components. The first argument represents a list of
 * groups the entity is in (expressed as numbers from 0 to 15). The second argument is a list
 * of groups that will be filtered against. When it is omitted, all groups are filtered against.
 *
 * @example
 * A RigidBody that is member of group 0 and will collide with everything from groups 0 and 1:
 *
 * ```tsx
 * <RigidBody collisionGroups={interactionGroups([0], [0, 1])} />
 * ```
 *
 * A RigidBody that is member of groups 0 and 1 and will collide with everything else:
 *
 * ```tsx
 * <RigidBody collisionGroups={interactionGroups([0, 1])} />
 * ```
 *
 * A RigidBody that is member of groups 0 and 1 and will not collide with anything:
 *
 * ```tsx
 * <RigidBody collisionGroups={interactionGroups([0, 1], [])} />
 * ```
 *
 * Please note that Rapier needs interaction filters to evaluate to true between _both_ colliding
 * entities for collision events to trigger.
 *
 * @param memberships Groups the collider is a member of. (Values can range from 0 to 15.)
 * @param filters Groups the interaction group should filter against. (Values can range from 0 to 15.)
 * @returns An InteractionGroup bitmask.
 */
export const interactionGroups = (
  memberships: number | number[],
  filters?: number | number[]
): InteractionGroups =>
  (bitmask(memberships) << 16) +
  (filters !== undefined ? bitmask(filters) : 0b1111_1111_1111_1111);

const bitmask = (groups: number | number[]): InteractionGroups =>
  [groups].flat().reduce((acc, layer) => acc | (1 << layer), 0);