ImageProcessor.swift

func mtlTexture(from image: UIImage) -> MTLTexture {
    //CGImage変換時に向きがおかしくならないように
    UIGraphicsBeginImageContext(image.size);
    image.draw(in: CGRect(x:0, y:0, width:image.size.width, height:image.size.height))
    let orientationImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    //CGImageに変換
    guard let cgImage = orientationImage?.cgImage else {
        fatalError("Can't open image \(image)")
    }
    //MTKTextureLoaderを使用してCGImageをMTLTextureに変換
    let textureLoader = MTKTextureLoader(device: self.device)
    do {
        let tex = try textureLoader.newTexture(cgImage: cgImage, options: nil)
        let textureDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: tex.pixelFormat, width: tex.width, height: tex.height, mipmapped: false)
        textureDescriptor.usage = [.shaderRead, .shaderWrite]
        return tex
    }
    catch {
        fatalError("Can't load texture")
    }
}