CGPathFromString.swift

import UIKit

@IBDesignable
class CharacterView: UIView {
    let pathLayer = CAShapeLayer()
    
    override func didMoveToSuperview() {
        if nil != superview {
            if pathLayer.superlayer != self.layer {
                self.layer.addSublayer(pathLayer)
                pathLayer.path = self.path(forAttributedString: AttributedString(string: "Italic System", attributes: [NSFontAttributeName : UIFont.italicSystemFont(ofSize: 33)]))
                pathLayer.fillColor = #colorLiteral(red: 0, green: 0, blue: 0, alpha: 1).cgColor
            }
            
            DispatchQueue.main.after(when: .now() + 1.0, execute: {
                let morph = CABasicAnimation(keyPath: "path")
                morph.duration = 1
                morph.toValue = self.path(forAttributedString: AttributedString(string: "System", attributes: [NSFontAttributeName : UIFont.systemFont(ofSize: 33)]))
                morph.fillMode = kCAFillModeForwards
                morph.isRemovedOnCompletion = false
                self.pathLayer.add(morph, forKey: "morph")
            })
        }
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        self.pathLayer.frame = self.bounds
    }
    
    func path(forAttributedString attributedString: AttributedString) -> CGPath {
        let line = CTLineCreateWithAttributedString(attributedString)
        let array = CTLineGetGlyphRuns(line) as [AnyObject]
        let paths = UIBezierPath()
        for ao in array {
            let run = ao as! CTRun
            let runAttributes = CTRunGetAttributes(run) as NSDictionary
            let runFont = runAttributes.object(forKey: NSFontAttributeName) as! CTFont
            let glyphCount = CTRunGetGlyphCount(run)
            for index in 0..<glyphCount {
                var glyph = CGGlyph()
                var point = CGPoint()
                CTRunGetGlyphs(run, CFRangeMake(index, 1), &glyph)
                CTRunGetPositions(run, CFRangeMake(index, 1), &point)
                var transform = CGAffineTransform(translationX: point.x, y: point.y)
                transform = transform.concat(CGAffineTransform(scaleX: 1, y: -1))
                guard let path = CTFontCreatePathForGlyph(runFont, glyph, &transform) else {
                    continue
                }
                paths.append(UIBezierPath(cgPath: path))
            }
        }
        paths.close()
        return paths.cgPath
    }
}