Swift2 Swift-GLKit查看过滤器图像

我试图使用

GLIKit视图

来修改图像。到目前为止，我使用的类在所有cifilter中都运行良好，除了

CILineOverlay

它呈现黑色视图。如果我使用其他效果，效果会很好

为什么

CILineOverlay

不显示

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)
        }
    }
}

苹果文档声明“图像中没有轮廓的部分是透明的。”-这意味着你正在黑色背景上画黑线。您可以简单地在白色背景上合成过滤器的输出，以使线条显示：

    let background = CIImage(color: CIColor(color: UIColor.whiteColor()))
        .imageByCroppingToRect(inputCIImage.extent)

    let finalImage = filter.outputImage!
        .imageByCompositingOverImage(background)

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如此明显，但同时并非如此。非常感谢！