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05-performance-and-large-datasets.md

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Performance and Large Datasets

LineChart supports built-in downsampling through chartPerformance(_:).

Modes

public enum ChartPerformanceMode {
    case none
    case automatic(threshold: Int, maxPoints: Int, simplifyLineStyle: Bool)
    case downsample(maxPoints: Int, simplifyLineStyle: Bool)
}

Recommended setup

LineChart()
    .chartData(largeSeries) // e.g. 2000+ points
    .chartPerformance(.automatic(
        threshold: 600,
        maxPoints: 180,
        simplifyLineStyle: true
    ))

What simplification changes

When simplifyLineStyle is enabled:

  • line style switches to straight
  • chart marks are disabled
  • line animation is disabled

This reduces render overhead for dense data.

For categorical data

For chartData([Double]), downsampled values are remapped to categorical slot indices to keep axis alignment stable.

Validation checklist

  1. Compare visual shape with and without downsampling.
  2. Ensure tooltips/selection still target expected points.
  3. Tune threshold and maxPoints for your dataset size and UI refresh rate.