---
title: "init(named:in:constantValues:)"
framework: realitykit
role: symbol
role_heading: Initializer
path: "realitykit/custommaterial/surfaceshader/init(named:in:constantvalues:)"
---

# init(named:in:constantValues:)

Creates a surface shader with the specified function constant values.

## Declaration

```swift
init(named name: String, in library: any MTLLibrary, constantValues: MTLFunctionConstantValues)
```

## Discussion

Discussion Function constants allow you to better share code or toggle features in your shaders without runtime performance costs by resolving their values at compile time. To use function constants, first define them within your metal code: constant bool kEnableBasicLighting [[function_constant(0)]];

[[stitchable]] void surfaceShader(realitykit::surface_parameters params) {     float3 baseColor = float3(1,0,0);     if (kEnableBasicLighting) {         float3 lighting = params.geometry().normal() * params.geometry().view_direction() * baseColor;         params.surface().set_emissive_color(half3(lighting));     } else {         params.surface().set_emissive_color(half3(baseColor));     } } Then initialize a surface shader with a Metal/MTLFunctionConstantValues object that defines values for your constants. let constants = MTLFunctionConstantValues() var yes = true funcConstants.setConstantValue(&yes, type: .bool, index: 0)

let geom = CustomMaterial.SurfaceShader.init(named: "surfaceShader", in: library, constantValues: constants)