How to Troubleshoot Playground CIFilter Error Message

Question

The code below should run fine: I didn't write it! :-)

I tried running some Swift Playground code by Simon J. Gladman (https://github.com/FlexMonkey) that corresponds to Chapter 8, "Warp Kernels," in his book, Core Image for Swift. As he wrote this code in Xcode 7.2 and I'm running it in Xcode 9.1, I had to update it in several places, which in most cases amounted to merely accepting the error handler's (or whatever it's called's) suggestions. After doing that, the following, more serious sounding message appeared:

error: Execution was interrupted, reason: signal SIGABRT. The process has been left at the point where it was interrupted, use "thread >return -x" to return to the state before expression evaluation.

Other than knowing that SIGABRT stands for "signal abort," I have no idea what it means or, more importantly, how to trouble shoot the error. (I'm still just learning Swift and Cocoa/Cocoa Touch. . . .) Suggestions would be appreciated.

//: ## Barrel Distortion Warp Filter

import UIKit
import CoreImage

//: ### Warp Kernel

class CRTWarpFilter: CIFilter
{
    var inputImage: CIImage?
    var bend: CGFloat = 3.2

    let crtWarpKernel = CIWarpKernel(source:
        "kernel vec2 crtWarp(vec2 extent, float bend)" +
            "{" +
            "   vec2 coord = ((destCoord() / extent) - 0.5) * 2.0;" +

            "   coord.x *= 1.0 + pow((abs(coord.y) / bend), 2.0);" +
            "   coord.y *= 1.0 + pow((abs(coord.x) / bend), 2.0);" +

            "   coord  = ((coord / 2.0) + 0.5) * extent;" +

            "   return coord;" +
        "}"
    )

    override var outputImage: CIImage!
    {
        if let inputImage = inputImage, let crtWarpKernel = crtWarpKernel
        {
            let arguments = [CIVector(x: inputImage.extent.size.width,
                                      y: inputImage.extent.size.height),
                             bend] as [Any]

            let extent = inputImage.extent

            return crtWarpKernel.apply(extent: extent,
                                       roiCallback:
                                           {(index, rect) in return rect},
                                       image: inputImage,
                                       arguments: arguments)
        }
        return nil
    }
}

let ciContext = CIContext()

func imageFromCIImage(source: CIImage) -> UIImage
{
    let cgImage = ciContext.createCGImage(source, from: source.extent)

    return UIImage(cgImage: cgImage!)
}

//: ### Swift Implementation of barrel warp kernel

//: `x` and `y` are pixel coordinates
let x = 65.0
let y = 55.0

//: `width` and `height` are extent
let width = 900.0
let height = 300.0

//: `crtWarpKernel` mechanics in Swift
var coordX = ((x / width) - 0.5) * 2.0
var coordY = ((y / height) - 0.5) * 2.0

coordX *= 1 + pow((abs(coordY) / 3.2), 2.0)
coordY *= 1 + pow((abs(coordX) / 3.2), 2.0)

coordX  = ((coordX / 2.0) + 0.5) * width
coordY  = ((coordY / 2.0) + 0.5) * height

// ----

let backgroundImage = CIFilter(name: "CICheckerboardGenerator",
                               withInputParameters: [
                                "inputColor0":
                                    CIColor(red: 0.1, green: 0.1, blue: 0.1),
                                "inputColor1":
                                    CIColor(red: 0.15, green: 0.15, blue: 0.15),
                                "inputCenter": CIVector(x: 0, y: 0),
                                "inputWidth": 50])!
    .outputImage!.cropped(to: CGRect(x: 1, y: 1,
                                     width: width - 2,
                                     height: height - 2))
    .composited(over: CIImage(color: CIColor(red: 0, green: 0, blue: 0)))
    .cropped(to: CGRect(origin: CGPoint.zero,
                        size: CGSize(width: width, height: height)))

let blueBox = CIImage(color: CIColor(red: 0.5, green: 0.5, blue: 1, alpha: 0.7))
    .cropped(to: CGRect(origin: CGPoint(x: coordX - 5, y: coordY - 5),
                        size: CGSize(width: 10, height: 10)))

let redBox = CIImage(color: CIColor(red: 1, green: 0, blue: 0, alpha: 0.7))
    .cropped(to: CGRect(origin: CGPoint(x: x - 5, y: y - 5),
                        size: CGSize(width: 10, height: 10)))

let warpFilter = CRTWarpFilter()

warpFilter.inputImage = backgroundImage

let composite = CIFilter(name: "CIAdditionCompositing",
                         withInputParameters: [
                            kCIInputBackgroundImageKey: warpFilter.outputImage,
                            kCIInputImageKey: blueBox])!
    .outputImage!
    .applyingFilter("CIAdditionCompositing",
                    parameters: [kCIInputBackgroundImageKey: redBox])

let result = composite

Answer 1

The playground does not like that inputImage is not declared as @objc. If you change this:

class CRTWarpFilter: CIFilter
{
    var inputImage: CIImage?

To this:

class CRTWarpFilter: CIFilter
{
    @objc var inputImage: CIImage?

It's going to work fine.

Here's your code updated to Xcode 11 and Swift 5

//: ## Barrel Distortion Warp Filter

import UIKit
import CoreImage

//: ### Warp Kernel

class CRTWarpFilter: CIFilter
{
    @objc var inputImage: CIImage?
    var bend: CGFloat = 3.2

    let crtWarpKernel = CIWarpKernel(source: """
        kernel vec2 crtWarp(vec2 extent, float bend)
        {
           vec2 coord = ((destCoord() / extent) - 0.5) * 2.0;

           coord.x *= 1.0 + pow((abs(coord.y) / bend), 2.0);
           coord.y *= 1.0 + pow((abs(coord.x) / bend), 2.0);

           coord  = ((coord / 2.0) + 0.5) * extent;

           return coord;
        }
    """)

    override var outputImage: CIImage?
    {
        if let inputImage = inputImage, let crtWarpKernel = crtWarpKernel
        {
            let arguments = [CIVector(x: inputImage.extent.size.width,
                                      y: inputImage.extent.size.height),
                             bend] as [Any]

            let extent = inputImage.extent

            return crtWarpKernel.apply(extent: extent,
                                       roiCallback:
                {(index, rect) in return rect},
                                       image: inputImage,
                                       arguments: arguments)
        }
        return nil
    }
}

let ciContext = CIContext()

func imageFromCIImage(source: CIImage) -> UIImage
{
    let cgImage = ciContext.createCGImage(source, from: source.extent)

    return UIImage(cgImage: cgImage!)
}

//: ### Swift Implementation of barrel warp kernel

//: `x` and `y` are pixel coordinates
let x = 65.0
let y = 55.0

//: `width` and `height` are extent
let width = 900.0
let height = 300.0

//: `crtWarpKernel` mechanics in Swift
var coordX = ((x / width) - 0.5) * 2.0
var coordY = ((y / height) - 0.5) * 2.0

coordX *= 1 + pow((abs(coordY) / 3.2), 2.0)
coordY *= 1 + pow((abs(coordX) / 3.2), 2.0)

coordX  = ((coordX / 2.0) + 0.5) * width
coordY  = ((coordY / 2.0) + 0.5) * height

// ----

let backgroundImage = CIFilter(name: "CICheckerboardGenerator",
                               parameters: [
                                "inputColor0":
                                    CIColor(red: 0.1, green: 0.1, blue: 0.1),
                                "inputColor1":
                                    CIColor(red: 0.15, green: 0.15, blue: 0.15),
                                "inputCenter": CIVector(x: 0, y: 0),
                                "inputWidth": 50])!
    .outputImage!.cropped(to: CGRect(x: 1, y: 1,
                                     width: width - 2,
                                     height: height - 2))
    .composited(over: CIImage(color: CIColor(red: 0, green: 0, blue: 0)))
    .cropped(to: CGRect(origin: CGPoint.zero,
                        size: CGSize(width: width, height: height)))

let blueBox = CIImage(color: CIColor(red: 0.5, green: 0.5, blue: 1, alpha: 0.7))
    .cropped(to: CGRect(origin: CGPoint(x: coordX - 5, y: coordY - 5),
                        size: CGSize(width: 10, height: 10)))

let redBox = CIImage(color: CIColor(red: 1, green: 0, blue: 0, alpha: 0.7))
    .cropped(to: CGRect(origin: CGPoint(x: x - 5, y: y - 5),
                        size: CGSize(width: 10, height: 10)))

let warpFilter = CRTWarpFilter()
warpFilter.inputImage = backgroundImage

let composite = CIFilter(name: "CIAdditionCompositing",
                         parameters: [
                            kCIInputBackgroundImageKey: warpFilter.outputImage,
                            kCIInputImageKey: blueBox])!
    .outputImage!
    .applyingFilter("CIAdditionCompositing",
                    parameters: [kCIInputBackgroundImageKey: redBox])

let result = composite