问如何在使用CAShapeLayer - Swift绘制的路径上标记点？

EN

func drawSemicircle() {

    // drawing an upper half of a circle -> 180 degree to 0 degree, clockwise
    let startAngle = CGFloat(M_PI)
    let endAngle = CGFloat(0.0)
    let centerPoint = CGPoint(x: CGRectGetWidth(frame)*0.5 , y: CGRectGetHeight(frame))
    let radius = frame.size.width*0.5 - 80.0 // radius of your arc

    // path set here
    let semiCircleLayer = CAShapeLayer()
    semiCircleLayer.frame = bounds // requried for layer calculations
    let semiCirclePath = UIBezierPath(arcCenter:centerPoint, radius:radius, startAngle:startAngle, endAngle:endAngle, clockwise: true)
    semiCircleLayer.path = semiCirclePath.CGPath

    // layer customisation
    semiCircleLayer.fillColor = UIColor.clearColor().CGColor
    semiCircleLayer.strokeColor = UIColor(red: 237.0/255.0, green: 236.0/255.0, blue: 236.0/255.0, alpha: 1.0).CGColor
    semiCircleLayer.lineWidth = 20.0
    semiCircleLayer.lineCap = kCALineCapButt
    layer.addSublayer(semiCircleLayer)


    // draw graduation (cue the wall of code!)

    let graduationLayer = CAShapeLayer() // the graduation layer that'll display the graduation
    graduationLayer.frame = semiCircleLayer.bounds

    let graduationWidth = CGFloat(4.0) // the width of the graduation
    let graduationLength = CGFloat(50.0) // the length of the graduation
    let graduationColor = UIColor.redColor() // the color of both the graduation line and text

    let startGradRad = radius-semiCircleLayer.lineWidth*0.5 // the starting radius of the graduation
    let endGradRad = startGradRad+graduationLength // the ending radius of the graduation

    let graduationAngle = CGFloat(M_PI*0.79) // 21% along the arc from the left (0 degrees coresponds to the right hand side of the circle, with the positive angle direction going anti-clocwise (much like a unit circle in maths), so we define 79% along the arc, from the right hand side)

    // the starting point of the graduation line. the angles are negative as the arc is effectively drawn upside-down in the UIKit coordinate system.
    let startGradPoint = CGPoint(x: cos(-graduationAngle)*startGradRad+centerPoint.x, y: sin(-graduationAngle)*startGradRad+centerPoint.y)
    let endGradPoint = CGPoint(x: cos(-graduationAngle)*endGradRad+centerPoint.x, y: sin(-graduationAngle)*endGradRad+centerPoint.y)

    // the path for the graduation line
    let graduationPath = UIBezierPath()
    graduationPath.moveToPoint(startGradPoint) // start point
    graduationPath.addLineToPoint(endGradPoint) // end point

    graduationLayer.path = graduationPath.CGPath // add path to the graduation shape layer

    // configure stroking options
    graduationLayer.fillColor = UIColor.clearColor().CGColor
    graduationLayer.strokeColor = graduationColor.CGColor
    graduationLayer.lineWidth = graduationWidth

    // add to semi-circle layer
    semiCircleLayer.addSublayer(graduationLayer)

    // the font of the text to render at the end of the graduation
    let textFont = UIFont.systemFontOfSize(30)

    // the text to render at the end of the graduation - do you custom value logic here
    let str : NSString = "value"

    // default paragraph style
    let paragraphStyle = NSParagraphStyle()

    // the text attributes dictionary. used to obtain a size of the drawn text in order to calculate its frame
    let textAttributes = [NSParagraphStyleAttributeName:paragraphStyle, NSFontAttributeName:textFont]

    // size of the rendered text
    let textSize = str.sizeWithAttributes(textAttributes)

    let xOffset = abs(cos(graduationAngle))*textSize.width*0.5 // the x-offset of the text from the end of the graduation line
    let yOffset = abs(sin(graduationAngle))*textSize.height*0.5 // the y-offset of the text from the end of the graduation line

    /// the padding between the graduation line and the text
    let graduationTextPadding = CGFloat(5.0)

    // bit of pythagorus to determine how far away the center of the text lies from the end of the graduation line. multiplying the values together is cheaper than using pow. the text padding is added onto it.
    let textOffset = sqrt(xOffset*xOffset+yOffset*yOffset)+graduationTextPadding

    // the center of the text to render
    let textCenter = CGPoint(x: cos(-graduationAngle)*textOffset+endGradPoint.x, y: sin(-graduationAngle)*textOffset+endGradPoint.y)

    // the frame of the text to render
    let textRect = CGRect(x: textCenter.x-textSize.width*0.5, y: textCenter.y-textSize.height*0.5, width: textSize.width, height: textSize.height)

    let textLayer = CATextLayer()
    textLayer.contentsScale = UIScreen.mainScreen().scale // to ensure the text is rendered at the screen scale
    textLayer.frame = textRect
    textLayer.string = str
    textLayer.font = textFont
    textLayer.fontSize = textFont.pointSize // required as CATextLayer ignores the font size of the font you pass
    textLayer.foregroundColor = graduationColor.CGColor // color of text
    graduationLayer.addSublayer(textLayer)
}