Initial label layer implementation

LKLabelLayer.swift

import QuartzCore
import UIKit

open class LKLabelLayer : CALayer {
    fileprivate var stringDrawingContext : NSStringDrawingContext!
    fileprivate var stringDrawingOptions : NSStringDrawingOptions!

    @objc open var attributedText : NSAttributedString?
    
    public override init() {
        super.init()
        commonInit()
    }
    
    public required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }
    
    private func commonInit() {
        stringDrawingOptions = [.usesFontLeading, 
                                .usesLineFragmentOrigin, 
                                .truncatesLastVisibleLine ]
        stringDrawingContext = NSStringDrawingContext()
        needsDisplayOnBoundsChange = true
        isOpaque = false
    }
 
    open override func draw(in ctx: CGContext) {
        drawText(in: ctx.boundingBoxOfClipPath)
    }
    
    fileprivate func drawText(in rect: CGRect) {
        attributedText?.draw(with: rect, 
                          options: stringDrawingOptions, 
                          context: stringDrawingContext)
    }
}