Add filled circles (markers) at SwiftUI path points - swift

Question

I'm trying to draw a line with markers at each point by using a Shape view in SwiftUI. I want the line to have a filled circle at each CGPoint on the line. The closest to this that I've gotten is by adding an arc at each point. Instead of using the arc, how can I add a Circle() shape at each point? I'm open to other approaches to accomplish this. My only requirements are to use SwiftUI and have the ability to interact with the markers.
import SwiftUI
struct LineShape: Shape {
let values: [Double]
func path(in rect: CGRect) -> Path {
let xStep = rect.width / CGFloat(values.count - 1)
var path = Path()
path.move(to: CGPoint(x: 0.0, y: (1 - values[0]) * Double(rect.height)))
for i in 1..<values.count {
let pt = CGPoint(x: Double(i) * Double(xStep), y: (1 - values[i]) * Double(rect.height))
path.addLine(to: pt)
path.addArc(center: pt, radius: 8, startAngle: Angle(degrees: 0), endAngle: Angle(degrees: 360), clockwise: false)
}
return path
}
}
struct ContentView: View {
var body: some View {
LineShape(values: [0.2, 0.4, 0.3, 0.8, 0.5])
.stroke(.red, lineWidth: 2.0)
.padding()
.frame(width: 400, height: 300)
}
}

Answer 1

You can make two different shapes, one for the line and one for the markers, and overlay them. Then you can also control their coloring individually:
struct LineShape: Shape {
let values: [Double]
func path(in rect: CGRect) -> Path {
let xStep = rect.width / CGFloat(values.count - 1)
var path = Path()
path.move(to: CGPoint(x: 0.0, y: (1 - values[0]) * Double(rect.height)))
for i in 1..<values.count {
let pt = CGPoint(x: Double(i) * Double(xStep), y: (1 - values[i]) * Double(rect.height))
path.addLine(to: pt)
}
return path
}
}
struct MarkersShape: Shape {
let values: [Double]
func path(in rect: CGRect) -> Path {
let xStep = rect.width / CGFloat(values.count - 1)
var path = Path()
for i in 1..<values.count {
let pt = CGPoint(x: Double(i) * Double(xStep), y: (1 - values[i]) * Double(rect.height))
path.addEllipse(in: CGRect(x: pt.x - 8, y: pt.y - 8, width: 16, height: 16))
}
return path
}
}
struct ContentView: View {
var body: some View {
LineShape(values: [0.2, 0.4, 0.3, 0.8, 0.5])
.stroke(.red, lineWidth: 2.0)
.overlay(
MarkersShape(values: [0.2, 0.4, 0.3, 0.8, 0.5])
.fill(.blue)
)
.frame(width: 350, height: 300)
}
}

Answer 2

According to previous posts and comments here is my solution:
First there is need to use extension for filling and setting shape stroke:
extension Shape {
public func fill<Shape: ShapeStyle>(_ fillContent: Shape, strokeColor: Color, lineWidth: CGFloat) -> some View {
ZStack {
self.fill(fillContent)
self.stroke(strokeColor, lineWidth: lineWidth)
}
}
}
Another thing is Scaler struct used to make scaling calculations:
struct Scaler {
let bounds: CGPoint
let maxVal: Double
let minVal: Double
let valuesCount: Int
var xFactor: CGFloat {
valuesCount < 2 ? bounds.x : bounds.x / CGFloat(valuesCount - 1)
}
var yFactor: CGFloat {
bounds.y / maxVal
}
}
Now it's time for real chart shape drawing:
struct ChartLineDotsShape: Shape {
let values: [Double]
let dotRadius: CGFloat
func path(in rect: CGRect) -> Path {
guard let maxVal = values.max(), let minVal = values.min() else { return Path() }
let scaler = Scaler(bounds: CGPoint(x: rect.width, y: rect.height), maxVal: maxVal, minVal: minVal, valuesCount: values.count)
return Path { path in
var valuesIterator = values.makeIterator()
let dx = scaler.xFactor
var x = 0.0
guard let y = valuesIterator.next() else { return }
path.move(to: CGPoint(x: x, y: calculate(y, scaler: scaler)))
draw(point: CGPoint(x: x, y: calculate(y, scaler: scaler)), on: &path)
x += dx
while let y = valuesIterator.next() {
draw(point: CGPoint(x: x, y: calculate(y, scaler: scaler)), on: &path)
x += dx
}
}
}
private func calculate(_ value: CGFloat, scaler: Scaler) -> CGFloat {
scaler.bounds.y - value * scaler.yFactor
}
private func draw(point: CGPoint, on path: inout Path) {
path.addLine(to: CGPoint(x: point.x, y: point.y))
path.addEllipse(in: CGRect(x: point.x - dotRadius * 0.5, y: point.y - dotRadius * 0.5, width: dotRadius, height: dotRadius))
path.move(to: CGPoint(x: point.x, y: point.y))
}
}
If there is single iteration loop lines dots drawing shape we can try to use it in some view:
public struct ChartView: View {
public var body: some View {
ChartLineDotsShape(values: [0.3, 0.5, 1.0, 2.0, 2.5, 2.0, 3.0, 6.0, 2.0, 1.5, 2.0], dotRadius: 4.0)
.fill(Color.blue, strokeColor: Color.blue, lineWidth: 1.0)
.shadow(color: Color.blue, radius: 2.0, x: 0.0, y: 0.0)
.frame(width: 320.0, height: 200.0)
.background(Color.blue.opacity(0.1))
.clipped()
}
}
Finally preview setup:
struct ChartView_Previews: PreviewProvider {
static var previews: some View {
ChartView()
.preferredColorScheme(.dark)
}
}
and viola: