Build Metal-based Core Image kernels with Xcode

3:08 - Put your kernels in .ci.metal sources

// MyKernels.ci.metal
#include <CoreImage/CoreImage.h> // includes CIKernelMetalLib.h
using namespace metal;

extern "C" float4 HDRZebra (coreimage::sample_t s, float time, coreimage::destination dest) 
{
	float diagLine = dest.coord().x + dest.coord().y;
	float zebra = fract(diagLine/20.0 + time*2.0);
	if ((zebra > 0.5) && (s.r > 1 || s.g > 1 || s.b > 1))
		return float4(2.0, 0.0, 0.0, 1.0);
	return s;
}

4:58 - Loading your kernel and applying it to create a new image

class HDRZebraFilter: CIFilter {
    var inputImage: CIImage?
	var inputTime: Float = 0.0

    static var kernel: CIColorKernel = { () -> CIColorKernel in 
	    let url = Bundle.main.url(forResource: "MyKernels", 
                                withExtension: "ci.metallib")!
		let data = try! Data(contentsOf: url)
		return try! CIColorKernel(functionName: "HDRzebra", 
                          fromMetalLibraryData: data)
	}()

  	override var outputImage : CIImage? {
		get {
			guard let input = inputImage else {return nil}
			return HDRZebraFilter.kernel.apply(extent: input.extent, 
											 arguments: [input, inputTime])
		}
	}
}