init(named:in:constantValues:)

Declaration

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

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 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.

let constants = MTLFunctionConstantValues()
var yes = true
funcConstants.setConstantValue(&yes, type: .bool, index: 0)

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