Swift - GLKit View CIFilter Image - swift2

Question

I am trying to use a GLIKit View in order to modify an Image. The class I have so far is working well all the CIFilters except for the CILineOverlay it renders a black view. If I use any other effect it works well.
Why is the CILineOverlay not showing?
class ImageView: GLKView {
let clampFilter = CIFilter(name: "CIAffineClamp")!
let blurFilter = CIFilter(name: "CILineOverlay")!
let ciContext:CIContext
override init(frame: CGRect) {
let glContext = EAGLContext(API: .OpenGLES2)
ciContext = CIContext(
EAGLContext: glContext,
options: [
kCIContextWorkingColorSpace: NSNull()
]
)
super.init(frame: frame, context: glContext)
enableSetNeedsDisplay = true
}
required init(coder aDecoder: NSCoder) {
let glContext = EAGLContext(API: .OpenGLES2)
ciContext = CIContext(
EAGLContext: glContext,
options: [
kCIContextWorkingColorSpace: NSNull()
]
)
super.init(coder: aDecoder)!
context = glContext
enableSetNeedsDisplay = true
}
#IBInspectable var inputImage: UIImage? {
didSet {
inputCIImage = inputImage.map { CIImage(image: $0)! }
}
}
#IBInspectable var blurRadius: Float = 0 {
didSet {
//blurFilter.setValue(blurRadius, forKey: "inputIntensity")
setNeedsDisplay()
}
}
var inputCIImage: CIImage? {
didSet { setNeedsDisplay() }
}
override func drawRect(rect: CGRect) {
if let inputCIImage = inputCIImage {
clampFilter.setValue(inputCIImage, forKey: kCIInputImageKey)
blurFilter.setValue(clampFilter.outputImage!, forKey: kCIInputImageKey)
let rect = CGRect(x: 0, y: 0, width: drawableWidth, height: drawableHeight)
ciContext.drawImage(blurFilter.outputImage!, inRect: rect, fromRect: inputCIImage.extent)
}
}
}

Answer 1

The Apple docs states "The portions of the image that are not outlined are transparent." - this means you are drawing black lines over a black background. You can simply composite the output from the filter over a white background to make the lines appear:
let background = CIImage(color: CIColor(color: UIColor.whiteColor()))
.imageByCroppingToRect(inputCIImage.extent)
let finalImage = filter.outputImage!
.imageByCompositingOverImage(background)