Swift Charts - weak scrolling performance

Question

junior_tjt OP

Created 2w

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Hello there!

I wanted to give a native scrolling mechanism for the Swift Charts Graph a try and experiment a bit if the scenario that we try to achieve might be possible, but it seems that the Swift Charts scrolling performance is very poor.

The graph was created as follows:

X-axis is created based on a date range,
Y-axis is created based on an integer values between moreless 0-320 value.
the graph is scrollable horizontally only (x-axis),
The time range (x-axis) for the scrolling content was set to one year from now date (so the user can scroll one year into the past as a minimum visible date (.chartXScale).
The X-axis shows 3 hours of data per screen width (.chartXVisibleDomain).
The data points for the graph are generated once when screen is about to appear so that the Charts engine can use it (no lazy loading implemented yet).
The line data points (LineMark views) consist of 2880 data points distributed every 5 minutes which simulates - two days of continuous data stream that we want to present. The rest of the graph displays no data at all.

The performance result:

The graph on the initial loading phase is frozen for about 10-15 seconds until the data appears on the graph.
Scrolling is very laggy - the CPU usage is 100% and is unacceptable for the end users.
If we show no data at all on the graph (so no LineMark views are created at all) - the result is similar - the empty graph scrolling is also very laggy.

Below I am sharing a test code:

@main
struct ChartsTestApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
            Spacer()
        }
    }
}

struct LineDataPoint: Identifiable, Equatable {
    var id: Int
    let date: Date
    let value: Int
}

actor TestData {
    func generate(startDate: Date) async -> [LineDataPoint] {
        var values: [LineDataPoint] = []
        
        for i in 0..<(1440 * 2) {
            values.append(
                LineDataPoint(
                    id: i,
                    date: startDate.addingTimeInterval(
                        TimeInterval(60 * 5 * i) // Every 5 minutes
                    ),
                    value: Int.random(in: 1...100)
                )
            )
        }
        
       return values
    }
}

struct ContentView: View {
    var startDate: Date {
        return endDate.addingTimeInterval(-3600*24*30*12) // one year into the past from now
    }
    let endDate = Date()
    
    @State var dataPoints: [LineDataPoint] = []
    
    var body: some View {
        Chart {
            ForEach(dataPoints) { item in
                LineMark(
                    x: .value("Date", item.date),
                    y: .value("Value", item.value),
                    series: .value("Series", "Test")
                )
            }
        }
        .frame(height: 200)
        .chartScrollableAxes(.horizontal)
        .chartYAxis(.hidden)
        .chartXScale(domain: startDate...endDate) // one year possibility to scroll back
        .chartXVisibleDomain(length: 3600 * 3) // 3 hours visible on screen
        .onAppear {
            Task {
                dataPoints = await TestData().generate(startDate: startDate)
            }
        }
    }
}

I would be grateful for any insights or suggestions on how to improve it or if it's planned to be improved in the future.

Currently, I use UIKit CollectionView where we split the graph into smaller chunks of the graph and we present the SwiftUI Chart content in the cells, so we use the scrolling offered there. I wonder if it's possible to use native SwiftUI for such a scenario so that later on we could also implement some kind of lazy loading of the data as the user scrolls into the past.

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