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feat: Add stroke support for LineChartBarData #2076

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feat: Add stroke support for LineChartBarData #2076

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2 changes: 2 additions & 0 deletions example/lib/presentation/samples/line/line_chart_sample2.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -146,6 +146,8 @@ class _LineChartSample2State extends State<LineChartSample2> {
maxY: 6,
lineBarsData: [
LineChartBarData(
strokeColor: Colors.red,
strokeWidth: 3,
spots: const [
FlSpot(0, 3),
FlSpot(2.6, 2),
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18 changes: 18 additions & 0 deletions lib/src/chart/line_chart/line_chart_data.dart
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Expand Up @@ -251,6 +251,8 @@ class LineChartBarData with EquatableMixin {
this.isStrokeJoinRound = false,
BarAreaData? belowBarData,
BarAreaData? aboveBarData,
this.strokeColor,
this.strokeWidth = 0,
this.dotData = const FlDotData(),
this.errorIndicatorData =
const FlErrorIndicatorData<LineChartSpotErrorRangeCallbackInput>(),
Expand Down Expand Up @@ -346,6 +348,14 @@ class LineChartBarData with EquatableMixin {
/// otherwise it draws line with hard edges.
final bool isCurved;

/// Optional border color for the line.
/// Useful for improving visibility when lines overlap.
final Color? strokeColor;
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@imaNNeo imaNNeo Apr 10, 2026

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Can we use the BorderSide class instead of defining strokeColor and strokeWidth here?
Because all other chart types in fl_chart use BorderSide for borders (e.g., BarChartRodData.borderSide, PieChartSectionData.borderSide).

Let's keep the API consistent:

final BorderSide borderSide; // default: BorderSide.none


/// Width of the border around the line.
/// Default is 0 (no border).
final double strokeWidth;

/// If [isCurved] is true, it determines smoothness of the curved edges.
final double curveSmoothness;

Expand Down Expand Up @@ -427,6 +437,8 @@ class LineChartBarData with EquatableMixin {
isStepLineChart: b.isStepLineChart,
lineChartStepData:
LineChartStepData.lerp(a.lineChartStepData, b.lineChartStepData, t),
strokeColor: Color.lerp(a.strokeColor, b.strokeColor, t),
strokeWidth: lerpDouble(a.strokeWidth, b.strokeWidth, t)!,
);

/// Copies current [LineChartBarData] to a new [LineChartBarData],
Expand Down Expand Up @@ -454,6 +466,8 @@ class LineChartBarData with EquatableMixin {
Shadow? shadow,
bool? isStepLineChart,
LineChartStepData? lineChartStepData,
Color? strokeColor,
double? strokeWidth,
}) =>
LineChartBarData(
spots: spots ?? this.spots,
Expand All @@ -479,6 +493,8 @@ class LineChartBarData with EquatableMixin {
shadow: shadow ?? this.shadow,
isStepLineChart: isStepLineChart ?? this.isStepLineChart,
lineChartStepData: lineChartStepData ?? this.lineChartStepData,
strokeColor: strokeColor ?? this.strokeColor,
strokeWidth: strokeWidth ?? this.strokeWidth,
);

/// Used for equality check, see [EquatableMixin].
Expand All @@ -505,6 +521,8 @@ class LineChartBarData with EquatableMixin {
shadow,
isStepLineChart,
lineChartStepData,
strokeColor,
strokeWidth,
];
}

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12 changes: 12 additions & 0 deletions lib/src/chart/line_chart/line_chart_painter.dart
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Expand Up @@ -281,6 +281,18 @@ class LineChartPainter extends AxisChartPainter<LineChartData> {
barData,
);
drawBarShadow(canvasWrapper, barPath, barData);
if (barData.strokeColor != null && barData.strokeWidth > 0) {
final borderPaint = Paint()
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@imaNNeo imaNNeo Apr 10, 2026

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There's a performance issue with creating the Paint() object in every frame.
Please create the Paint instance once (in the constructor, just like other Paint() objects) and reuse it here.

..color = barData.strokeColor!
..strokeWidth = barData.barWidth + (barData.strokeWidth * 2)
..style = PaintingStyle.stroke
..strokeCap =
barData.isStrokeCapRound ? StrokeCap.round : StrokeCap.butt
..strokeJoin =
barData.isStrokeJoinRound ? StrokeJoin.round : StrokeJoin.miter;

canvasWrapper.canvas.drawPath(barPath, borderPaint);
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@imaNNeo imaNNeo Apr 10, 2026

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This line bypasses the canvas wrapper. All drawing must go through canvasWrapper.drawPath(...)

So please use .drawPath() directly on the canvasWrapper

}
drawBar(canvasWrapper, barPath, barData, holder);
}
}
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