chartScrollableAxes moves axis

Question

I am trying to implement a horizontal scrollable chart. However, the y axis moves along when scrolling. How can I make the y axis stay put?

Here is my code:

struct DataPoint: Identifiable {
    var id = UUID()
    let x: Double
    let y: Double
}

let minGlobalX: Double = 0
let maxGlobalX: Double = 100

let data: [DataPoint] = (Int(minGlobalX) ..< Int(maxGlobalX)).map { DataPoint(x: Double($0), y: Double(arc4random()) / Double(UInt32.max)) }

struct ContentView: View {
    var body: some View {
        Chart(data) {
            LineMark(
                x: .value("x", $0.x),
                y: .value("y", $0.y)
            )
            .lineStyle(StrokeStyle(lineWidth: 1))
        }
        .chartScrollableAxes(.horizontal)
        .chartXScale(domain: [minGlobalX, maxGlobalX])
        .chartXAxis {
            AxisMarks(position: .bottom, values: [0]) {
                AxisGridLine(stroke: .init(lineWidth: 1))
            }
        }
        .chartYScale(domain: [0, 1])
        .chartYAxis {
            AxisMarks(position: .leading, values: [0]) {
                AxisGridLine(stroke: .init(lineWidth: 1))
            }
        }
        .padding(20)
    }
}

Sweeper · Accepted Answer · 2025-03-17 19:29:12Z

1

The axis lines are just AxisGridLines positioned at the "0" position of the chart. When you scroll the chart, the "0" position moves, and so the line moves with it as well.

You can add the lines using a chartOverlay instead. Position some 1-wide Rectangles using ChartProxy.plotContainerFrame:

.chartOverlay { proxy in
    GeometryReader { geo in
        let plotContainer = geo[proxy.plotContainerFrame!]
        Rectangle()
            .frame(width: 1, height: plotContainer.height)
            .offset(x: plotContainer.minX, y: plotContainer.minY)
        Rectangle()
            .frame(width: plotContainer.width, height: 1)
            .offset(x: plotContainer.minX, y: plotContainer.maxY)
    }
}

answered Mar 17 at 19:29

Sweeper

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3 Comments

koen Mar 17 at 19:36

Thanks, this works. I kept my example simple, and in the complete chart there are also tickmarks and labels. I guess I would have to draw those also in the chartOverlay?

Sweeper Mar 17 at 19:43

@koen You don't have to. AxisTick and AxisValueLabel doesn't interfere with this.

koen Mar 22 at 14:50

For completeness, chartYAxisLabel is also moving, so I am now drawing these in the chartOverlay as well.

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