# init(group:mask:) Creates a collision filter. ``` init(group: CollisionGroup, mask: CollisionGroup) ``` ## Parameters `group` The collision group identifier. `mask` The collision mask defines what objects will collide with objects using this filter. ## Discussion Collision filters are created for the collision group specified in the `group` parameter. The `mask` parameter defines which objects will collide with the objects that use this filter. Because [`CollisionGroup`](/documentation/RealityKit/CollisionGroup) conforms to , you can specify any combination of collision groups in the `mask` parameter by using the various methods like `CollisionGroup/union(_:)`, `CollisionGroup/subtracting(_:)`, and `CollisionGroup/intersection(_:)`. Entities from any group contained in `mask` will collide with entities using this filter, while those not contained by `mask` will not. To combine multiple groups into a filter, use the `CollisionGroup/union(_:)` method, like this: ```swift let groupA = CollisionGroup(rawValue: 1 << 0) let groupB = CollisionGroup(rawValue: 1 << 1) let groupC = CollisionGroup(rawValue: 1 << 2) // Create a filter that collides with A and C, but not B let theFilter = CollisionFilter(group: groupA, mask: groupA.union(groupB)) ``` A common use case is to want entities to collide with everything except one group, or a few groups. In a game, for example, you might not want a player’s pieces to collide with their own pieces, or you might not want players on the same team to collide with each other. You can accomplish that by starting with the [`all`](/documentation/RealityKit/CollisionGroup/all) property, subtracting the group or groups that you don’t want the entities using this filter to collide with, like this: ```swift // Create a filter that collides with everything except B let notGroupB = CollisionGroup.all.subtracting(groupB) ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)