ReversedFont

That code renders any font as reversed font.

How to use:

1. Create custom NSLayoutManager

class TransparentLayoutManager: NSLayoutManager {

    override func showCGGlyphs(glyphs: UnsafePointer<CGGlyph>, positions: UnsafePointer<CGPoint>, count glyphCount: Int, font: UIFont, matrix textMatrix: CGAffineTransform, attributes: [String : AnyObject], inContext graphicsContext: CGContext) {
        guard attributes[NSBackgroundColorAttributeName] != nil else {
            super.showCGGlyphs(glyphs, positions: positions, count: glyphCount, font: font, matrix: textMatrix, attributes: attributes, inContext: graphicsContext)
            return
        }
        
        CGContextSaveGState(graphicsContext)
        CGContextSetBlendMode(graphicsContext, .DestinationOut)
        super.showCGGlyphs(glyphs, positions: positions, count: glyphCount, font: font, matrix: textMatrix, attributes: attributes, inContext: graphicsContext)
        CGContextRestoreGState(graphicsContext)
    }
    
}

2. Create a textview and use it

private let textView: UITextView = {
        let textStorage = NSTextStorage()
        let layoutManager = TransparentLayoutManager()
        let container = NSTextContainer(size: CGSize.zero)
        container.widthTracksTextView = true
        container.heightTracksTextView = true
        layoutManager.addTextContainer(container)
        textStorage.addLayoutManager(layoutManager)
        
        return UITextView(frame: CGRect.zero, textContainer: container)
    }()