From 6a54eff247b4762dac6429eb3b3e8e2e3918f1fd Mon Sep 17 00:00:00 2001
From: Marius Gripsgard <marius@slipper.no>
Date: Wed, 17 Apr 2024 02:19:41 +0200
Subject: [PATCH] Add curved step line edges

---
 lib/src/chart/line_chart/line_chart_data.dart    | 16 ++++++++++++++++
 lib/src/chart/line_chart/line_chart_painter.dart | 10 ++++++++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/lib/src/chart/line_chart/line_chart_data.dart b/lib/src/chart/line_chart/line_chart_data.dart
index c24127acf..831819e18 100644
--- a/lib/src/chart/line_chart/line_chart_data.dart
+++ b/lib/src/chart/line_chart/line_chart_data.dart
@@ -240,6 +240,8 @@ class LineChartBarData with EquatableMixin {
     this.dashArray,
     this.shadow = const Shadow(color: Colors.transparent),
     this.isStepLineChart = false,
+    this.isStepLineEdgesCurved = false,
+    this.stepLineEdgesSmoothness = 2,
     this.lineChartStepData = const LineChartStepData(),
   })  : color =
             color ?? ((color == null && gradient == null) ? Colors.cyan : null),
@@ -360,6 +362,12 @@ class LineChartBarData with EquatableMixin {
   /// If sets true, it draws the chart in Step Line Chart style, using [LineChartBarData.lineChartStepData].
   final bool isStepLineChart;
 
+  /// if sets true, it draws the chart in Step Line Chart style with curved edges.
+  final bool isStepLineEdgesCurved;
+
+  /// If [isStepLineEdgesCurved] is true, it determines the curve smoothness of the step line edges.
+  final double stepLineEdgesSmoothness;
+
   /// Holds data for representing a Step Line Chart, and works only if [isStepChart] is true.
   final LineChartStepData lineChartStepData;
 
@@ -392,6 +400,8 @@ class LineChartBarData with EquatableMixin {
       showingIndicators: b.showingIndicators,
       shadow: Shadow.lerp(a.shadow, b.shadow, t)!,
       isStepLineChart: b.isStepLineChart,
+      isStepLineEdgesCurved: b.isStepLineEdgesCurved,
+      stepLineEdgesSmoothness: b.stepLineEdgesSmoothness,
       lineChartStepData:
           LineChartStepData.lerp(a.lineChartStepData, b.lineChartStepData, t),
     );
@@ -418,6 +428,8 @@ class LineChartBarData with EquatableMixin {
     List<int>? showingIndicators,
     Shadow? shadow,
     bool? isStepLineChart,
+    bool? isStepLineEdgesCurved,
+    double? stepLineEdgesSmoothness,
     LineChartStepData? lineChartStepData,
   }) {
     return LineChartBarData(
@@ -441,6 +453,8 @@ class LineChartBarData with EquatableMixin {
       showingIndicators: showingIndicators ?? this.showingIndicators,
       shadow: shadow ?? this.shadow,
       isStepLineChart: isStepLineChart ?? this.isStepLineChart,
+      isStepLineEdgesCurved: isStepLineEdgesCurved ?? this.isStepLineEdgesCurved,
+      stepLineEdgesSmoothness: stepLineEdgesSmoothness ?? this.stepLineEdgesSmoothness,
       lineChartStepData: lineChartStepData ?? this.lineChartStepData,
     );
   }
@@ -466,6 +480,8 @@ class LineChartBarData with EquatableMixin {
         dashArray,
         shadow,
         isStepLineChart,
+        isStepLineEdgesCurved,
+        stepLineEdgesSmoothness,
         lineChartStepData,
       ];
 }
diff --git a/lib/src/chart/line_chart/line_chart_painter.dart b/lib/src/chart/line_chart/line_chart_painter.dart
index b0f7c6cbd..d61da2355 100644
--- a/lib/src/chart/line_chart/line_chart_painter.dart
+++ b/lib/src/chart/line_chart/line_chart_painter.dart
@@ -590,10 +590,16 @@ class LineChartPainter extends AxisChartPainter<LineChartData> {
         path.lineTo(next.dx, next.dy);
       } else {
         final deltaX = next.dx - current.dx;
+        final isYIncreasing = current.dy < next.dy;
+
+        // ignore 2 last points
+        final smoothness = i + 2 < size ? (barData.isStepLineEdgesCurved ? barData.stepLineEdgesSmoothness : 0) : 0;
 
         path
-          ..lineTo(current.dx + deltaX - (deltaX * stepDirection), current.dy)
-          ..lineTo(current.dx + deltaX - (deltaX * stepDirection), next.dy)
+          ..lineTo(current.dx + deltaX - (deltaX * stepDirection) - smoothness, current.dy)
+          ..quadraticBezierTo(current.dx + deltaX - (deltaX * stepDirection), current.dy, current.dx + deltaX - (deltaX * stepDirection), current.dy + (isYIncreasing ? smoothness : -smoothness))
+          ..lineTo(current.dx + deltaX - (deltaX * stepDirection), next.dy + (isYIncreasing ? -smoothness : smoothness))
+          ..quadraticBezierTo(current.dx + deltaX - (deltaX * stepDirection), next.dy, current.dx + deltaX - (deltaX * stepDirection) + smoothness, next.dy)
           ..lineTo(next.dx, next.dy);
       }
     }