AnimatedChart.swift

import Charts
import SwiftUI

struct Sample: Identifiable {
    var x: Double
    var y: Double

    var id: some Hashable { x }
}

struct AnimatedChart: View, Animatable {
    var animatableData: Double  = 0

    init(x: Double) {
        self.animatableData = x
    }

    let samples = stride(from: -1, through: 1, by: 0.01).map {
        Sample(x: $0, y: pow($0, 3))
    }

    var body: some View {
        VStack {
            Chart {
                // Ideally, there'd be a way to not evaluate this every time.
                ForEach(samples) { sample in
                    LineMark(x: .value("x", sample.x), y: .value("y", sample.y))
                }

                PointMark(
                    x: .value("x", animatableData),
                    y: .value("y", pow(animatableData, 3))
                )
            }
        }
    }
}

struct AnimatedChart_Previews: PreviewProvider {
    struct Preview: View {
        @State
        var x: Double = -1

        var body: some View {
            VStack {
                AnimatedChart(x: x)
                    .aspectRatio(1, contentMode: .fit)
                    .padding()

                Spacer()
            }
            .contentShape(Rectangle())
            .onTapGesture {
                withAnimation(.linear(duration: 2)) {
                    x = 1
                }
            }
        }
    }

    static var previews: some View {
        Preview()
    }
}