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 uint32_t kChannelIndex [[function_constant(0)]];

[[stitchable]]
void postLightingShader(realitykit::post_lighting_parameters params, constant void *customParams) RK_AVAILABILITY_IOS_27 RK_AVAILABILITY_MACOS_27
{
   if (kChannelIndex < 4) {
       half4 color = params.lighting().color();
       color.rgb = color[kChannelIndex];
       color.a = 1.0h;
       params.lighting().set_color(color);
   }
}

Then initialize a post-lighting shader with a Metal/MTLFunctionConstantValues object that defines values for your constants.

let constants = MTLFunctionConstantValues()
var channelIndex : UInt32 = 3
funcConstants.setConstantValue(&channelIndex, type: .uint, index: 0)

let postLighting = CustomMaterial.PostLightingShader.init(named: "postLightingShader", in: library, constantValues: constants)