# init(floatLiteral:) Creates an object to specify the amount of roughness, using a single value that applies to the entire material. ``` init(floatLiteral value: Float) ``` ## Parameters `value` The roughness value. ## Discussion The `roughness` property represents how much the surface of the entity scatters light that it reflects. A material with a high roughness has a matte appearance, and one with a low roughness has a shiny appearance. -1@2x.png) The following Swift code shows how to specify roughness using a single value for the entire entity: ```swift material.roughness = PhysicallyBasedMaterial.Roughness(floatLiteral: 0.0) ``` With custom materials, the roughness value is available in your surface shader; however, RealityKit doesn’t use it automatically to render the entity. To render an entity with roughness, the material’s [`lightingModel`](/documentation/RealityKit/CustomMaterial/lightingModel-swift.property) needs to be [`CustomMaterial.LightingModel.lit`](/documentation/RealityKit/CustomMaterial/LightingModel-swift.enum/lit) or [`CustomMaterial.LightingModel.clearcoat`](/documentation/RealityKit/CustomMaterial/LightingModel-swift.enum/clearcoat), and call `params.surface().set_roughness()` from its surface shader function. The following Metal code shows how to retrieve the roughness value set using this initializer in your surface shader: ```other // Retrieve the roughness scale from the CustomMaterial. float roughnessScale = params.material_constants().roughness_scale(); // Set the roughness value using the roughness scale. params.surface().set_roughness(roughnessScale); ``` For more information on creating custom materials and writing shader functions, see [Modifying RealityKit rendering using custom materials](/documentation/RealityKit/modifying-realitykit-rendering-using-custom-materials). --- 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)