# LightmapResource.AtlasReference Specifies an area in a lightmap atlas to fetch data from. ``` struct AtlasReference ``` ## Topics ### Locating the atlas texture [`var atlasTextureIndex: Int`](/documentation/RealityKit/LightmapResource/AtlasReference/atlasTextureIndex) Index of the atlas within the LightmapResource. [`var atlasTextureSlice: Int`](/documentation/RealityKit/LightmapResource/AtlasReference/atlasTextureSlice) Index of the slice within the atlas. ### Mapping texture coordinates [`var uvScale: SIMD2`](/documentation/RealityKit/LightmapResource/AtlasReference/uvScale) A scale to apply to lightmap UV attribute before sampling from the slice of the atlas. Note that lightmap textures use the Metal convention: UV (0,0) corresponds to the top-left corner of the image, while UV (1,1) corresponds to the bottom-right. [`var uvOffset: SIMD2`](/documentation/RealityKit/LightmapResource/AtlasReference/uvOffset) An offset to apply to lightmap UV attribute before sampling from the slice of the atlas. Note that lightmap textures use the Metal convention: UV (0,0) corresponds to the top-left corner of the image, while UV (1,1) corresponds to the bottom-right. ### Initializers [`init()`](/documentation/RealityKit/LightmapResource/AtlasReference/init()) ## Relationships ### Conforms To [`Sendable`](/documentation/Swift/Sendable) [`SendableMetatype`](/documentation/Swift/SendableMetatype) --- 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)