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

# init(named:in:)

Creates a geometry modifier object from a named function in a Metal library.

## Declaration

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

## Parameters

- `name`: The name of the geometry modifier function.
- `library`: The Metal library that contains the function.

## Discussion

Discussion To create a geometry modifier function for a custom material, create a Metal file in your Xcode project. Prefix the function with the keyword [[visible]]. The function needs to take a single parameter of type realitykit::geometry_parameters. Here’s what a minimal geometry modifier function looks like: #include <metal_stdlib> #include <RealityKit/RealityKit.h> using namespace metal;

[[visible]] void myGeometryModifier(realitykit::geometry_parameters params) {     // Use params.geometry().set_model_position_offset() to move the vertex. } To create a custom material using this shader, get a reference to your app’s Metal library. You can do that like this: guard let device = MTLCreateSystemDefaultDevice() else {     fatalError("Error creating default metal device.") } guard let library = maybeDevice.makeDefaultLibrary() else {     fatalError("Error creating default metal library") } Once you’ve got a reference to your Metal library, use it to create the surface shader reference like this: let geometryModifier = CustomMaterial.GeometryModifier(     named: "myGeometryModifier",     in: library ) important: RealityKit loads surface shader functions by name, so the name of your surface shader function needs to be unique and exactly match the name parameter. For more information on creating custom materials and writing shader functions, see Modifying RealityKit rendering using custom materials.