# LowLevelMaterialResource.SurfaceShader.Descriptor The name and library for a user-authored Metal surface shader function. ``` struct Descriptor ``` ## Topics ### Creating a descriptor [`init(named: String, in: any MTLLibrary, constantValues: MTLFunctionConstantValues)`](/documentation/RealityKit/LowLevelMaterialResource/SurfaceShader/Descriptor/init(named:in:constantValues:)) Creates a descriptor referencing the named function in the given library, with the provided function constant values. [`init(named: String, in: any MTLLibrary, constantValues: MTLFunctionConstantValues, uniformsSize: Int)`](/documentation/RealityKit/LowLevelMaterialResource/SurfaceShader/Descriptor/init(named:in:constantValues:uniformsSize:)) Creates a descriptor for a surface shader that accepts a custom uniforms argument buffer. [`init(named: String, in: any MTLLibrary, constantValues: MTLFunctionConstantValues, uniformsType: UniformsType.Type)`](/documentation/RealityKit/LowLevelMaterialResource/SurfaceShader/Descriptor/init(named:in:constantValues:uniformsType:)) Creates a descriptor for a surface shader that accepts a custom uniforms argument buffer, deriving the buffer size from `uniformsType`. ### Configuring the shader function [`var library: any MTLLibrary`](/documentation/RealityKit/LowLevelMaterialResource/SurfaceShader/Descriptor/library) The Metal library that contains the function. [`var constantValues: MTLFunctionConstantValues`](/documentation/RealityKit/LowLevelMaterialResource/SurfaceShader/Descriptor/constantValues) The constant values to use when creating the function. These correspond to constants defined in your Metal code. ### Initializers [`init(named: String, in: any MTLLibrary)`](/documentation/RealityKit/LowLevelMaterialResource/SurfaceShader/Descriptor/init(named:in:)) Creates a descriptor referencing the named function in the given library. ### Instance Properties [`var name: String`](/documentation/RealityKit/LowLevelMaterialResource/SurfaceShader/Descriptor/name) The name of the Metal function in the library. ## Relationships ### Conforms To [`SendableMetatype`](/documentation/Swift/SendableMetatype) [`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)