# init(_:) Creates a roughness object from a physically based material’s roughness property. ``` init(_ value: PhysicallyBasedMaterial.Roughness) ``` ## Parameters `value` The physically based material’s roughness property. ## Discussion This initializer creates a roughness object by copying the scale and texture values from an existing [`PhysicallyBasedMaterial.Roughness`](/documentation/RealityKit/PhysicallyBasedMaterial/Roughness-swift.struct) object. With custom materials, the `texture` and `scale` properties of the [`CustomMaterial.Roughness`](/documentation/RealityKit/CustomMaterial/Roughness-swift.struct) object are available in your surface shader function, but RealityKit doesn’t automatically use them when rendering your entity. To render an entity with roughness, set [`lightingModel`](/documentation/RealityKit/CustomMaterial/lightingModel-swift.property) to [`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. To achieve the same roughness behavior as [`PhysicallyBasedMaterial`](/documentation/RealityKit/PhysicallyBasedMaterial), the surface shader function multiplies roughness scale by the sampled value from the texture, as the following Metal code demonstrates: ```swift // Retrieve the roughness scale from the CustomMaterial. float roughnessScale = params.material_constants().roughness_scale(); // Retrieve the entity's UV texture coordinates. float2 uv = params.geometry().uv0(); // Models loaded from USDZ or Reality Composer use UVs that are flipped // on the y-axis. This compensates for that. uv.y = 1.0 - uv.y; // Sample the texture based on the resulting UVs. auto tex = params.textures(); half roughness = tex.roughness().sample(textureSampler, uv).r; // Multiply the scale and the sampled value from the texture, and assign // the result to the shader's base color property. roughness *= roughnessScale; // Set the roughness value to be used by the custom material shader. params.surface().set_roughness(roughness); ``` 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)