Gavin Wiggins

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Path markers

Written on November 13, 2022

Markers can be added to a line path by stacking two views in a ZStack. The line is drawn as a path using LineShape while the markers (filled circles) are created in the MarkersView.

import SwiftUI

struct MarkersView: View {

    let values: [Double]

    var body: some View {
        GeometryReader { geom in
            let xStep = geom.size.width / CGFloat(values.count - 1)

            ForEach(0..<values.count) {
                Circle()
                    .fill(.blue)
                    .frame(width: 10)
                    .position(x: CGFloat($0) * xStep, y: (1 - values[$0]) * geom.size.height)
            }
        }
    }
}

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]) * rect.height))

        for i in 1..<values.count {
            let pt = CGPoint(x: Double(i) * xStep, y: (1 - values[i]) * rect.height)
            path.addLine(to: pt)
        }

        return path
    }
}

struct LineView: View {

    let values: [Double]

    var body: some View {
        ZStack {
            MarkersView(values: values)
            LineShape(values: values)
                .stroke(.red, lineWidth: 2)
        }
    }
}

struct ContentView: View {
    var body: some View {
        LineView(values: [0.2, 0.4, 0.3, 0.8, 0.5])
            .padding()
            .frame(minWidth: 400, minHeight: 300)
    }
}