Drawing a scale on semi-circle Swift/UIView - ios

Question

Imagine I am having a full semi-circle from 0 to Pi from the unit circle. There is a small number on the left side named min and a big number on the right side called max. There are both interchangeable inside the app depending on some factors.
Does anybody of you have a nice idea on how to draw a scale like I did in the drawing below? I would like to have longer lines for every x mod 10 = 0 and three larger ones in between. The grey circle is just for orientation.
So I started with the following piece of code:
let radius = CGFloat(40)
let dashLong = CGFloat(10)
let dashShort = CGFloat(5)
let middle = CGPoint(x: 50, y: 50)
let leftAngle = CGFloat(Double.pi)
let rightAngle = CGFloat(0)
let min = 45 //random num
let max = 117 //random num
let innerPath = UIBezierPath(arcCenter: middle, radius: radius, startAngle: rightAngle, endAngle: leftAngle, clockwise: true)
let middlePath = UIBezierPath(arcCenter: middle, radius: radius+dashShort, startAngle: rightAngle, endAngle: leftAngle, clockwise: true)
let outerPath = UIBezierPath(arcCenter: middle, radius: radius+dashLong, startAngle: rightAngle, endAngle: leftAngle, clockwise: true)
So there is a radius and also the length of the two types of dashes in the scale. I chose 45 and 117 as random integers for the extrem values of the scale. My three paths which do not need to be drawn are just an orientation on where the dashes need to be started and ended on. So for 50,60,...110 there start at the innerPath and go to the outer one, I am pretty sure that must be in the same angle for a dash on all circles.
Does anyone has a very smart idea how to continue this to calc the dashes and draw them without getting messed up code?

Answer 1

Here's the math for drawing a tick mark.
Let's do everything as CGFloat to keep the conversions to a minimum:
let radius: CGFloat = 40
let dashLong: CGFloat = 10
let dashShort: CGFloat 5
let middle = CGPoint(x: 50, y: 50)
let leftAngle: CGFloat = .pi
let rightAngle: CGFloat = 0
let min: CGFloat = 45 //random num
let max: CGFloat = 117 //random num
First, compute your angle.
let value: CGFloat = 50
let angle = (max - value)/(max - min) * .pi
Now compute your two points:
let p1 = CGPoint(x: middle.x + cos(angle) * radius,
y: middle.y - sin(angle) * radius)
// use dashLong for a long tick, and dashShort for a short tick
let radius2 = radius + dashLong
let p2 = CGPoint(x: middle.x + cos(angle) * radius2,
y: middle.y - sin(angle) * radius2)
Then draw a line between p1 and p2.
Note: In iOS, the coordinate system is upside down with +Y being down, which is why the sin calculation is subtracted from middle.y.
Complete Example
enum TickStyle {
case short
case long
}
class ScaleView: UIView {
// ScaleView properties. If any are changed, redraw the view
var radius: CGFloat = 40 { didSet { self.setNeedsDisplay() } }
var dashLong: CGFloat = 10 { didSet { self.setNeedsDisplay() } }
var dashShort: CGFloat = 5 { didSet { self.setNeedsDisplay() } }
var middle = CGPoint(x: 50, y: 50) { didSet { self.setNeedsDisplay() } }
var leftAngle: CGFloat = .pi { didSet { self.setNeedsDisplay() } }
var rightAngle: CGFloat = 0 { didSet { self.setNeedsDisplay() } }
var min: CGFloat = 45 { didSet { self.setNeedsDisplay() } }
var max: CGFloat = 117 { didSet { self.setNeedsDisplay() } }
override func draw(_ rect: CGRect) {
let path = UIBezierPath()
// draw the arc
path.move(to: CGPoint(x: middle.x - radius, y: middle.y))
path.addArc(withCenter: middle, radius: radius, startAngle: leftAngle, endAngle: rightAngle, clockwise: true)
let startTick = ceil(min / 2.5) * 2.5
let endTick = floor(max / 2.5) * 2.5
// add tick marks every 2.5 units
for value in stride(from: startTick, through: endTick, by: 2.5) {
let style: TickStyle = value.truncatingRemainder(dividingBy: 10) == 0 ? .long : .short
addTick(at: value, style: style, to: path)
}
// stroke the path
UIColor.black.setStroke()
path.stroke()
}
// add a tick mark at value with style to path
func addTick(at value: CGFloat, style: TickStyle, to path: UIBezierPath) {
let angle = (max - value)/(max - min) * .pi
let p1 = CGPoint(x: middle.x + cos(angle) * radius,
y: middle.y - sin(angle) * radius)
var radius2 = radius
if style == .short {
radius2 += dashShort
} else if style == .long {
radius2 += dashLong
}
let p2 = CGPoint(x: middle.x + cos(angle) * radius2,
y: middle.y - sin(angle) * radius2)
path.move(to: p1)
path.addLine(to: p2)
}
}
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let view = ScaleView(frame: CGRect(x: 50, y: 50, width: 100, height: 60))
view.backgroundColor = .yellow
self.view.addSubview(view)
}
}
Picture of scale running in app:

Answer 2

My suggestion is Draw this semi circle in CALayer and Draw lines from centre of the semi circle in different CALayer and Mask both of them so that It appears Like this