# init(named:in:constantValues:uniformsSize:) Creates a descriptor for a surface shader that accepts a custom uniforms argument buffer. ``` init(named name: String, in library: any MTLLibrary, constantValues: MTLFunctionConstantValues = .init(), uniformsSize: Int) ``` ## Parameters `name` The name of the Metal function in the library. `library` The Metal library that contains the function. `constantValues` The Metal function constant values to specialize the function with. The function descriptor takes a snapshot of the constant values passed in. `uniformsSize` The size of the custom uniforms buffer, in bytes. ## Discussion Use this initializer when your Metal surface shader function reads per-draw parameters through a custom uniforms argument buffer, using the same mechanism as [`CustomMaterial/withMutableUniforms(ofType:stage:_:)`](https://developer.apple.com/documentation/realitykit/custommaterial/withmutableuniforms(oftype:stage:_:)). The function must be `[[stitchable]]` and declare the uniforms as a second `constant T &customParams` parameter: ```cpp [[stitchable]] void mySurfaceShader(realitykit::surface_parameters params, constant MyUniforms &customParams) { ... } ``` The renderer sizes the uniforms buffer to `uniformsSize` bytes and configures the argument table automatically. --- 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)