List<FlSpot> lttbDownsample(List<FlSpot> data, int threshold) { if (data.length <= threshold) return data; final sampled = <FlSpot>[data.first]; final bucketSize = (data.length - 2) / (threshold - 2); var a = 0; for (var i = 0; i < threshold - 2; i++) { final rangeStart = (i * bucketSize + 1).floor(); final rangeEnd = ((i + 1) * bucketSize + 1).floor().clamp(0, data.length); final nextA = ((i + 1) * bucketSize + 1).floor().clamp(0, data.length - 1); double maxArea = -1; int maxAreaPoint = rangeStart; for (var j = rangeStart; j < rangeEnd; j++) { final area = (data[a].x * (data[nextA].y - data[j].y) + data[nextA].x * (data[j].y - data[a].y) + data[j].x * (data[a].y - data[nextA].y)) .abs() / 2; if (area > maxArea) { maxArea = area; maxAreaPoint = j; } } sampled.add(data[maxAreaPoint]); a = maxAreaPoint; } sampled.add(data.last); return sampled; } 

500 points instead of 5000—FPS returns to 60. LTTB reduces rendering time by 10x compared to full dataset.

Downsampling Methods Comparison

For mobile charts, LTTB is the optimal balance.

3-Step Downsampling Integration Guide

1. Choose LTTB algorithm—best speed-quality ratio for line charts.
2. Prepare data—filter out nulls and NaNs, convert to FlSpot array.
3. Integrate into LineChart—replace source array with lttbDownsample result before passing to LineChartData.

Data Entry Animations

Line drawing animation left-to-right is a popular UX pattern. On Flutter, use AnimationController + TweenAnimationBuilder, limiting visible points by the animated value t:

TweenAnimationBuilder<double>( tween: Tween(begin: 0.0, end: 1.0), duration: const Duration(milliseconds: 800), curve: Curves.easeOut, builder: (context, value, _) { final visiblePoints = (allSpots.length * value).round(); return LineChart( LineChartData( lineBarsData: [ LineChartBarData(spots: allSpots.take(visiblePoints).toList()), ], ), ); }, ) 

For bar charts, animate bar growth using the fromY parameter with an AnimatedContainer.

Real-Time Updates Without FPS Loss

Charts that update every second (metrics, stock data) require calling setState only for changed data. The wrong way: calling setState on the whole screen—rebuilds entire widget tree. The right way: use ValueNotifier + ValueListenableBuilder around only the chart widget.

1. Define a maximum number of displayed points (sliding window).
2. Use ValueNotifier to hold the point list.
3. Update the notifier when new data arrives.

final chartData = ValueNotifier<List<FlSpot>>([]); // In widget: ValueListenableBuilder<List<FlSpot>>( valueListenable: chartData, builder: (_, spots, __) => LineChart(LineChartData( lineBarsData: [LineChartBarData(spots: spots)], )), ) // When new point arrives: void addDataPoint(double x, double y) { final current = [...chartData.value, FlSpot(x, y)]; if (current.length > maxPoints) current.removeAt(0); // sliding window chartData.value = current; } 

Making Charts Accessible

Charts are invisible to VoiceOver/TalkBack without extra work. Minimum: wrap chart in a Semantics widget describing what it shows. For financial or medical apps, provide a toggleable table alternative. This meets WCAG 2.1 and App Store Review Guidelines (Section 5.1).

What's Included in Our Work

• Library selection justified by project requirements
• Implementation of required chart types (line, bar, pie, candlestick, etc.)
• Performance optimization (downsampling, rendering)
• Data entry animations
• Interactivity: zoom, pan, tooltip on touch
• Accessibility support
• Integration with real-time data sources

Timeline and Cost

One chart type with basic interactivity: 2–3 days. A set of 3–5 types with animations and real-time updates: 1–2 weeks. Cost is determined individually—contact us for a project estimate. Save up to 50% of development time through downsampling. Order a turnkey solution: get a consultation on library selection and optimization. Our engineers will help you save time and budget.