问CAShapeLayer分辨率

EN

let backLayer = CAShapeLayer()
    backLayer.anchorPoint = CGPoint(x: 0.5, y: 0.5)
    backLayer.bounds = backBounds
    backLayer.backgroundColor = color
    backLayer.cornerRadius = cornerRadius
    backLayer.position = position
    backLayer.shadowColor = UIColor.blackColor().CGColor
    backLayer.shadowOffset = CGSize(width: shadowWidth, height: shadowWidth)
    backLayer.shadowOpacity = 0.5
    backLayer.shadowRadius = shadowRadius
    backLayer.contentsScale = UIScreen.mainScreen().scale
    let subPosition = CGPoint(x: backLayer.bounds.height / 2  + dipper, y: backLayer.bounds.height / 2)


    // Border Layer
    let borderLayer = CAShapeLayer()
    borderLayer.bounds = CGRect(x: 0.0  , y: 0.0, width: backLayer.bounds.width - dipper, height: backLayer.bounds.height)
    borderLayer.position = subPosition
    borderLayer.anchorPoint = CGPoint(x: 0.5, y: 0.5)
    borderLayer.cornerRadius = cornerRadius
    borderLayer.borderColor = color
    borderLayer.borderWidth = borderWidth
    borderLayer.shadowColor = UIColor.blackColor().CGColor
    borderLayer.shadowOffset = CGSize(width: 1, height: 1)
    borderLayer.shadowRadius = shadowRadius
    borderLayer.shadowOpacity = 0.6
    borderLayer.contentsScale = UIScreen.mainScreen().scale



    // char layer
    let charLayer = CATextLayer()
    charLayer.bounds = borderLayer.bounds
    charLayer.anchorPoint = CGPoint(x: 0.5, y: 0.5)
    charLayer.position = subPosition
    charLayer.string = NSString(UTF8String: char)
    charLayer.alignmentMode = kCAAlignmentCenter
    charLayer.wrapped = true
    charLayer.shadowColor = UIColor.blackColor().CGColor
    charLayer.shadowOffset = CGSize(width: shadowWidth / 3, height: shadowWidth / 3)
    charLayer.shadowRadius = 2
    charLayer.shadowOpacity = 0.8
    charLayer.truncationMode = kCATruncationMiddle
    charLayer.font = "BookmanOldStyle-Bold"
    charLayer.fontSize = height / 1.4
    charLayer.contentsScale = UIScreen.mainScreen().scale