CoreImageHelpers

CoreImageHelpers.swift

// MARK - CoreImage

private let sharedContext = CIContext(options: [kCIContextPriorityRequestLow: true])

/// Core Image helper methods.
public extension UIImage {
    /// Applies closure with a filter to the image.
    ///
    // Performance considerations. Chaining multiple CIFilter objects is much
    /// more efficient then using ProcessorComposition to combine multiple
    /// instances of CoreImageFilter class. Avoid unnecessary texture transfers
    /// between the CPU and GPU.
    ///
    /// - parameter context: Core Image context, uses shared context by default.
    /// - parameter filter: Closure for applying image filter.
    public func applyFilter(context: CIContext = sharedContext, closure: (CIImage) -> CIImage?) -> UIImage? {
        func inputImage(for image: UIImage) -> CIImage? {
            if let image = image.cgImage {
                return CIImage(cgImage: image)
            }
            if let image = image.ciImage {
                return image
            }
            return nil
        }
        guard let inputImage = inputImage(for: self), let outputImage = closure(inputImage) else {
            return nil
        }
        guard let imageRef = context.createCGImage(outputImage, from: inputImage.extent) else {
            return nil
        }
        return UIImage(cgImage: imageRef, scale: scale, orientation: imageOrientation)
    }
    
    /// Applies filter to the image.
    ///
    /// - parameter context: Core Image context, uses shared context by default.
    /// - parameter filter: Image filter.
    public func applyFilter(_ filter: CIFilter?, context: CIContext = sharedContext) -> UIImage? {
        guard let filter = filter else {
            return nil
        }
        return applyFilter(context: context) {
            filter.setValue($0, forKey: kCIInputImageKey)
            return filter.outputImage
        }
    }
}