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 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)