How to mark points on a path drawn using CAShapeLa

I have a custom path drawn using CAShapeLayer in a UIView. Its a semicircle, upper half, drawn from left to right.

Following is the code used, writted in a UIView subclass:

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 = CGPointMake(CGRectGetWidth(frame)/2 , CGRectGetHeight(frame))

        // path set here
        let semirCircleLayer = CAShapeLayer()
        let semirCirclePath = UIBezierPath(arcCenter:centerPoint, radius: CGRectGetWidth(frame)/2 - 20.0 , startAngle:startAngle, endAngle:endAngle, clockwise: true)
        semirCircleLayer.path = semirCirclePath.CGPath

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

Current path looks like this:

What I am tryign to implement is to mark some points on the bar .Like a analog clock graduation + diigts, but not so complex. Just mark 1 point at any progress level. So a final output, something like this :

Can I get some help on this?

You'll want to use another `CAShapeLayer` for the graduation line and a `CATextLayer` for the text at the end of the graduation.

Instead of doing Core Graphics drawing as my answer here does, I recommend you use a 100% layer approach as to best fit in with your existing code.

Something like this should do the trick:

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)
}

Output:

There's quite a lot of code here, as you have to do some extra logic in order to calculate the size of the CATextLayer. You could simplify this by using a UILabel as you can use sizeToFit in order to calculate the size, however this may complicate the layer hierarchy.

I've tried my best to explain each line of code - but if you still have questions, I'll be happy to answer them!

Furthermore, if you re-structure the code, you could easily allow for the graduation angle, as well as the other variables to be changed from outside the class. I've provided an example of this in the full project below.