[[可缝合]]金属核心图像 CIKernel 失败

看起来[[stitchable]]Metal Core Image 内核由于未找到 Core Imagesampler.coord()和符号而无法在编译时链接，或者如果我添加其他 Metal 链接器标志（这对于可缝合内核来说并不是必需的），则sampler.sample(coord)无法在运行时加载。-fcikernel

这是github上测试项目的完整链接。欢迎下载并玩一玩。

我发现罪魁祸首是 Metal 文件中的这一行，链接器无法解析：

 float2 srcCoord = inputImage.coord();

我的代码摘录：

import CoreImage

class FilterTwo: CIFilter {
var inputImage: CIImage?
var inputParam: Float = 0.0

static var kernel: CIKernel = { () -> CIKernel in
   let url = Bundle.main.url(forResource: "default",
                            withExtension: "metallib")!
   let data = try! Data(contentsOf: url)

    let kernelNames = CIKernel.kernelNames(fromMetalLibraryData: data)
    NSLog("Kernels \(kernelNames)")
   return try! CIKernel(functionName: "secondFilter", fromMetalLibraryData: data) //<-- This fails!
}()

override var outputImage : CIImage? {
    guard let inputImage = inputImage else {
        return nil
    }
    
    return FilterTwo.kernel.apply(extent: inputImage.extent, roiCallback: { (index, rect) in
        return rect }, arguments: [inputImage])
}

}

这是金属文件：

 #include <CoreImage/CoreImage.h> // includes CIKernelMetalLib.h

 using namespace metal;

 [[ stitchable ]] half4 secondFilter (coreimage::sampler inputImage, coreimage::destination dest)
{
   float2 srcCoord = inputImage.coord();
   half4 color =  half4(inputImage.sample(srcCoord));

   return color;
}

这是用法：

       class ViewController: UIViewController {

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.
    
    let filter = FilterTwo()
    filter.inputImage = CIImage(color: CIColor.red)
    let outputImage = filter.outputImage!
    
    NSLog("Output \(outputImage)")
}

}

和输出：

     StitchableKernelsTesting/FilterTwo.swift:15: Fatal error: 'try!' expression unexpectedly raised an error: Error Domain=CIKernel Code=1 "(null)" UserInfo={CINonLocalizedDescriptionKey=Function does not exist in library data. …•∆}
   Kernels []

   reflect Function 'secondFilter' does not exist.