Data Visualization

Data Visualization for Flutter

Use this skill when building data visualizations in Flutter applications. The data_visualization package suite provides D3.js-like functionality for Flutter.

Installation

Add to pubspec.yaml:

dependencies:
  data_visualization: ^1.0.0

Or add individual packages as needed (see Package Reference below).

Core Concepts

Scales (dv_scale)

Transform data values to visual coordinates:

import 'package:dv_scale/dv_scale.dart';

// Linear scale for continuous data
final xScale = scaleLinear(domain: [0, 100], range: [0, 400]);

// Band scale for categorical data (bar charts)
final bandScale = scaleBand(domain: ['A', 'B', 'C'], range: [0, 300]);

// Time scale for dates
final timeScale = scaleTime(
  domain: [DateTime(2024, 1, 1), DateTime(2024, 12, 31)],
  range: [0, 800],
);

// Ordinal scale for color mapping
final colorScale = scaleOrdinal(
  domain: ['cat1', 'cat2'],
  range: [Colors.red, Colors.blue],
);

Curves (dv_curve)

Smooth line interpolation:

import 'package:dv_curve/dv_curve.dart';

final points = [Point(0, 10), Point(50, 80), Point(100, 30)];
final curve = curveCatmullRom();
final smoothPoints = curve.generate(points);

// Available: curveLinear(), curveBasis(), curveCardinal(),
// curveMonotoneX(), curveStep(), curveNatural()

Shapes (dv_shape)

Generate paths for chart elements:

import 'package:dv_shape/dv_shape.dart';

// Line generator
final lineGen = LineGenerator<Point>(
  x: (d, i) => xScale(d.x),
  y: (d, i) => yScale(d.y),
  curve: curveCatmullRom(),
);

// Area generator
final areaGen = AreaGenerator<Point>(
  x: (d, i) => xScale(d.x),
  y0: (d, i) => yScale(0),
  y1: (d, i) => yScale(d.y),
);

// Pie layout
final pieGen = PieGenerator<Map>(value: (d, i) => d['value']);
final arcs = pieGen.generate(data);

// Arc generator
final arcGen = ArcGenerator(
  innerRadius: 50, outerRadius: 100,
  startAngle: 0, endAngle: math.pi / 2,
);

Geographic (dv_geo_core, dv_geo)

Map projections and GeoJSON:

import 'package:dv_geo_core/dv_geo_core.dart';

// Projections
final mercator = geoMercator(center: (0, 0), scale: 100, translate: Point(200, 200));
final orthographic = geoOrthographic(center: (0, 0), scale: 150, translate: center, rotate: (-30, 0, 0));
final equirect = geoEquirectangular(center: (0, 0), scale: 100, translate: center);

// Project (lon, lat) -> (x, y)
final projected = mercator.project(-74.0, 40.7);

// GeoJSON
final geojson = GeoJsonFeatureCollection.fromJson(jsonData);
final geoPath = GeoPath(mercator);
final paths = geoPath.generate(geojson);

Hierarchy (dv_hierarchy)

Hierarchical data layouts:

import 'package:dv_hierarchy/dv_hierarchy.dart';

final root = HierarchyNode<Map>(
  data: {'name': 'root'},
  children: [
    HierarchyNode(data: {'name': 'A', 'value': 100}),
    HierarchyNode(data: {'name': 'B', 'value': 200}),
  ],
);

root.sum((d) => (d['value'] as num?)?.toDouble() ?? 0);

// Layouts - each sets x0, y0, x1, y1 or x, y, r on nodes
treemapLayout(root, width: 400, height: 300);
treeLayout(root, width: 400, height: 300);
packLayout(root, width: 400, height: 400);
clusterLayout(root, width: 400, height: 300);
partitionLayout(root, width: 400, height: 300);

Common Chart Patterns

Line Chart

class LineChartPainter extends CustomPainter {
  final List<Point> data;
  LineChartPainter(this.data);

  @override
  void paint(Canvas canvas, Size size) {
    final xScale = scaleLinear(domain: [0, data.length - 1], range: [50, size.width - 20]);
    final yScale = scaleLinear(domain: [0, 100], range: [size.height - 40, 20]);

    final curve = curveCatmullRom();
    final points = data.map((p) => Point(xScale(p.x), yScale(p.y))).toList();
    final curvePoints = curve.generate(points);

    final path = Path()..moveTo(curvePoints.first.x, curvePoints.first.y);
    for (final p in curvePoints.skip(1)) {
      path.lineTo(p.x, p.y);
    }

    canvas.drawPath(path, Paint()
      ..color = Colors.blue
      ..strokeWidth = 2
      ..style = PaintingStyle.stroke);
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => true;
}

Bar Chart

class BarChartPainter extends CustomPainter {
  final List<Map<String, dynamic>> data;
  BarChartPainter(this.data);

  @override
  void paint(Canvas canvas, Size size) {
    final labels = data.map((d) => d['label'] as String).toList();
    final values = data.map((d) => d['value'] as double).toList();

    final xScale = scaleBand(domain: labels, range: [50, size.width - 20], padding: 0.2);
    final yScale = scaleLinear(domain: [0, values.reduce(math.max)], range: [size.height - 40, 20]);

    for (int i = 0; i < data.length; i++) {
      final x = xScale(labels[i])!;
      final y = yScale(values[i]);
      canvas.drawRect(
        Rect.fromLTWH(x, y, xScale.bandwidth, yScale(0) - y),
        Paint()..color = Colors.indigo,
      );
    }
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => true;
}

Pie Chart

class PieChartPainter extends CustomPainter {
  final List<Map<String, dynamic>> data;
  PieChartPainter(this.data);

  @override
  void paint(Canvas canvas, Size size) {
    final center = Offset(size.width / 2, size.height / 2);
    final radius = math.min(size.width, size.height) / 2 - 20;

    final pie = PieGenerator<Map>(value: (d, i) => d['value'] as double);
    final arcs = pie.generate(data);
    final colors = [Colors.blue, Colors.red, Colors.green, Colors.orange];

    for (int i = 0; i < arcs.length; i++) {
      final arc = arcs[i];
      final arcGen = ArcGenerator(
        innerRadius: radius * 0.5,
        outerRadius: radius,
        startAngle: arc.startAngle,
        endAngle: arc.endAngle,
      );

      canvas.save();
      canvas.translate(center.dx, center.dy);
      canvas.drawPath(arcGen.generate(), Paint()..color = colors[i % colors.length]);
      canvas.restore();
    }
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => true;
}

Geographic Map

class GeoMapPainter extends CustomPainter {
  final GeoJsonFeatureCollection worldData;
  GeoMapPainter(this.worldData);

  @override
  void paint(Canvas canvas, Size size) {
    final center = Point(size.width / 2, size.height / 2);
    final proj = geoMercator(center: (0, 0), scale: size.width / 6, translate: center);

    final geoPath = GeoPath(proj);
    final paths = geoPath.generate(worldData);

    for (final pathPoints in paths) {
      if (pathPoints.length < 3) continue;
      final path = Path()..moveTo(pathPoints.first.x, pathPoints.first.y);
      for (int i = 1; i < pathPoints.length; i++) {
        path.lineTo(pathPoints[i].x, pathPoints[i].y);
      }
      path.close();
      canvas.drawPath(path, Paint()..color = Colors.green.shade300);
    }
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => true;
}

Package Reference

Resources

• Live Demo: https://gsmlg-app.github.io/data_visualization/
• GitHub: https://github.com/gsmlg-dev/data_visualization
• pub.dev: https://pub.dev/packages/data_visualization