UILabel使用transform.scale放大后，文字变虚

继承UILabel，子类代码如下：

public class ScaleLabel: UILabel {
    
    public override class var layerClass: AnyClass {
        return CATiledLayer.classForCoder()
    }
    
    public override init(frame: CGRect) {
        super.init(frame: frame)
        if let _layer = self.layer as? CATiledLayer {
            _layer.levelsOfDetail = 10
            _layer.levelsOfDetailBias = 10
        }
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

参考： iOS 超大高清图展示策略 TileLayer 及 levelsOfDetailBias 分析