# CustomMaterial.SurfaceShader The custom material’s surface shader function. ``` struct SurfaceShader ``` ## Overview Custom materials work together with a surface shader function to render entities. The [`CustomMaterial`](/documentation/RealityKit/CustomMaterial) properties related to rendering, such as [`baseColor`](/documentation/RealityKit/CustomMaterial/baseColor-swift.property) and [`normal`](/documentation/RealityKit/CustomMaterial/normal-swift.property), are available in the surface shader function, but RealityKit doesn’t use them directly. Instead, the material’s surface shader function allows you to calculate or specify all the material parameters that RealityKit uses to render your entity, such as [`baseColor`](/documentation/RealityKit/CustomMaterial/baseColor-swift.property), [`normal`](/documentation/RealityKit/CustomMaterial/normal-swift.property), and [`roughness`](/documentation/RealityKit/CustomMaterial/roughness-swift.property). RealityKit’s fragment shader calls your surface shader function once for each pixel it renders. Here’s a simple example of a surface shader that sets the entity’s base color: ```cpp #include #include // Specify the current default namespace as metal so that it's not // necessary to prefix Metal Standard Library symbols. using namespace metal; [[visible]] void mySurfaceShader(realitykit::surface_parameters params) { // Set the base color params.surface().set_base_color(half3(1.0, 0.5, 0.5)); } ``` 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). ## Topics ### Creating surface shader objects [`init(named: String, in: any MTLLibrary)`](/documentation/RealityKit/CustomMaterial/SurfaceShader/init(named:in:)) Creates a surface shader object from a named function in a Metal library. ### Accessing surface shader properties [`var name: String`](/documentation/RealityKit/CustomMaterial/SurfaceShader/name) The name of the surface shader function. [`var library: any MTLLibrary`](/documentation/RealityKit/CustomMaterial/SurfaceShader/library) The Metal library that contains this surface shader function. ### Initializers [`init(named: String, in: any MTLLibrary, constantValues: MTLFunctionConstantValues)`](/documentation/RealityKit/CustomMaterial/SurfaceShader/init(named:in:constantValues:)) Creates a surface shader with the specified function constant values. ## Relationships ### Conforms To [`Equatable`](/documentation/Swift/Equatable) [`SendableMetatype`](/documentation/Swift/SendableMetatype) [`Hashable`](/documentation/Swift/Hashable) [`MaterialFunction`](/documentation/RealityKit/MaterialFunction) [`Sendable`](/documentation/Swift/Sendable) --- 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)