RealityFoundation · IOS API REFERENCE

CustomMaterial.GeometryModifier

struct · iOS 15.0+ · SDK 27.1

struct GeometryModifier

The custom material’s optional shader function that can manipulate an entity’s vertex data. A geometry modifier is an optional Metal function that you can use with custom materials. Use a geometry modifier to change vertex data, such as vertex position, color, or texture coordinates. For example, offsetting a vertex’s position changes the size and shape of the entity for rendering only. If your custom material has a geometry modifier, RealityKit’s custom material vertex shader calls it once for each vertex in the entity. Changes that your geometry modifier makes are transient and don’t affect the vertex positions of the original ``ModelEntity``. Here’s a simple example of a geometry modifier that offsets the vertex positions along the z-axis based on the elapsed time: ```cpp #include <metal_stdlib> #include <RealityKit/RealityKit.h> using namespace metal; [[visible]] void myGeometryModifier(realitykit::geometry_parameters params) { float3 zOffset = float3(0.0, 0.0, params.uniforms().time() / 50.0); params.geometry().set_world_position_offset(zOffset); } ``` For more information on creating custom materials and writing shader functions, see <doc:modifying-realitykit-rendering-using-custom-materials>.

Members (8)

get · iOS 18.0+

constantValues

TypeScript

get constantValues(): _Metal_MTLFunctionConstantValues

Swift declaration

var constantValues: MTLFunctionConstantValues { get set }

The constant values to use when RealityKit creates your function. These correspond to constants defined in your metal code.

set · iOS 18.0+

constantValues

TypeScript

set constantValues(value: _Metal_MTLFunctionConstantValues)

Swift declaration

var constantValues: MTLFunctionConstantValues { get set }

The constant values to use when RealityKit creates your function. These correspond to constants defined in your metal code.

get · iOS 15.0+

name

TypeScript

get name(): string

Swift declaration

var name: String

The name of the geometry modifier function. This is the name of the Metal function that the custom material uses as its geometry modifier. The name needs to match the name of a Metal function in your Xcode project without parameters or parentheses.

set · iOS 15.0+

name

TypeScript

set name(value: string)

Swift declaration

var name: String

init · iOS 18.0+

init

TypeScript

static initNamedInConstantValues(name: string, library: SDKHandle, constantValues: _Metal_MTLFunctionConstantValues): CustomMaterial_GeometryModifier

Swift declaration

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

Creates a geometry modifier with the specified function constant values. 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: ```cpp constant bool kEnableVertexAnimation [[function_constant(0)]]; [[stitchable]] void geometryModifier(realitykit::geometry_parameters params) { if (kEnableVertexAnimation) { float currentTime = params.uniforms().time() * 0.5; params.geometry().set_model_position_offset(sin(currentTime) * 0.1 * params.geometry().normal()); } } ``` Then initialize a geometry modifier with a ``Metal/MTLFunctionConstantValues`` object that defines values for your constants. ```swift let constants = MTLFunctionConstantValues() var yes = true funcConstants.setConstantValue(&yes, type: .bool, index: 0) let geom = CustomMaterial.GeometryModifier.init(named: "geometryModifier", in: library, constantValues: constants) ```

init · iOS 15.0+

init

TypeScript

static initNamedIn(name: string, library: SDKHandle): CustomMaterial_GeometryModifier

Swift declaration

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

Creates a geometry modifier object from a named function in a Metal library. 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: ```cpp #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: ```swift 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: ```swift 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 <doc:modifying-realitykit-rendering-using-custom-materials>. - Parameters: - name: The name of the geometry modifier function. - library: The Metal library that contains the function.

get · iOS 15.0+

library

TypeScript

get library(): SDKHandle

Swift declaration

var library: any MTLLibrary { get set }

The Metal library that contains this surface shader function.

set · iOS 15.0+

library

TypeScript

set library(value: SDKHandle)

Swift declaration

var library: any MTLLibrary { get set }

The Metal library that contains this surface shader function.

Skipped declarations

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