BlurTrial.swift

let blur = GPUImageGaussianSelectiveBlurFilter()
    
    func addBlur() {
        gpuImage?.removeAllTargets()
        
        blur.blurRadiusInPixels = 20.0
        
        blur.excludeBlurSize = 0.0
        blur.excludeCircleRadius = 0.0
        
        blur.excludeCirclePoint = CGPoint(x: 0.5, y: 0.5)
        
        blur.aspectRatio = 1.3
        
        gpuImage?.addTarget(blur)
        blur.addTarget(gpuImageView)
        gpuImage?.processImage()
    }

    let minimumZoom: CGFloat = 0.0
    let maximumZoom: CGFloat = 4.0
    var lastZoomFactor: CGFloat = 0.3
    
    @IBAction func pinched(_ pinch: UIPinchGestureRecognizer) {
        
        func minMaxZoom(_ factor: CGFloat) -> CGFloat {
            return min(min(max(factor, minimumZoom), maximumZoom), 1)
        }
        
        func update(scale factor: CGFloat) {
            blur.excludeBlurSize = factor / 3
            blur.excludeCircleRadius = factor
            gpuImage?.processImage()
        }
        
        let newScaleFactor = minMaxZoom(pinch.scale * lastZoomFactor)
        
        switch pinch.state {
        case .began: fallthrough
        case .changed: update(scale: newScaleFactor)
        case .ended:
            lastZoomFactor = minMaxZoom(newScaleFactor)
            update(scale: lastZoomFactor)
        default: break
        }
    }
    
    @IBAction func tapHandler(_ gestureRecognizer: UITapGestureRecognizer) {
        let location = gestureRecognizer.location(in: currentImageView)
        blur.excludeCirclePoint = CGPoint(x: location.x / currentImageView.bounds.width, y: location.y / currentImageView.bounds.height)
        gpuImage?.processImage()
    }