iOS: CIColorKernel applyWithExtent warning message
<p>I'm trying to make original CIFilter with CIKernel.</p>

<p>code is here.</p>

<pre><code>var kernel: CIKernel?
var inputImage: CIImage?

override init() {
    super.init()
    self.kernel = createKernel()
}

required init(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)!
    self.kernel = createKernel()
}

func outputCustomImage() -&gt; CIImage? {

    if let inputImage = self.inputImage {
        let dod = inputImage.extent.insetBy(dx: -1, dy: -1)
        let args = [inputImage as AnyObject]

        let callback: CIKernelROICallback = {
        (index, rect) in
            return rect.insetBy(dx: -1, dy: -1)
        }

        return kernel!.applyWithExtent(dod, roiCallback: callback, arguments: args)
    }
    return nil
}

private func createKernel() -&gt; CIKernel {
    let kernelString =
        "kernel vec4 RGB_to_GBR(sampler source_image)\n" +
            "{\n" +
            "vec4 originalColor, twistedColor;\n" +
            "originalColor = sample(source_image, samplerCoord(source_image));\n" +
            "twistedColor.r = originalColor.g;\n" +
            "twistedColor.g = originalColor.b;\n" +
            "twistedColor.b = originalColor.r ;\n" +
            "twistedColor.a = originalColor.a;\n" +
            "return twistedColor;\n" +
    "}\n"

    return CIKernel(string: kernelString)!
}
</code></pre>

<p>and warning message is</p>

<blockquote>
  <p>Note: CIColorKernel applyWithExtent:roiCallback:arguments: ignores callback and is not recomended.  Use applyWithExtent:arguments: instead.</p>
</blockquote>