Add gradient for PieChart

lib/src/chart/pie_chart/pie_chart_data.dart

@@ -150,6 +150,7 @@ class PieChartSectionData {
   PieChartSectionData({
     double? value,
     Color? color,
+    this.gradient,
     double? radius,
     bool? showTitle,
     this.titleStyle,
@@ -178,6 +179,9 @@ class PieChartSectionData {
   /// Defines the color of section.
   final Color color;
 
+  /// Defines the gradient of section. If specified, overrides the color setting.
+  final Gradient? gradient;
+
   /// Defines the radius of section.
   final double radius;
 
@@ -218,6 +222,7 @@ class PieChartSectionData {
   PieChartSectionData copyWith({
     double? value,
     Color? color,
+    Gradient? gradient,
     double? radius,
     bool? showTitle,
     TextStyle? titleStyle,
@@ -230,6 +235,7 @@ class PieChartSectionData {
     return PieChartSectionData(
       value: value ?? this.value,
       color: color ?? this.color,
+      gradient: gradient ?? this.gradient,
       radius: radius ?? this.radius,
       showTitle: showTitle ?? this.showTitle,
       titleStyle: titleStyle ?? this.titleStyle,
@@ -252,6 +258,7 @@ class PieChartSectionData {
     return PieChartSectionData(
       value: lerpDouble(a.value, b.value, t),
       color: Color.lerp(a.color, b.color, t),
+      gradient: Gradient.lerp(a.gradient, b.gradient, t),
       radius: lerpDouble(a.radius, b.radius, t),
       showTitle: b.showTitle,
       titleStyle: TextStyle.lerp(a.titleStyle, b.titleStyle, t),

lib/src/chart/pie_chart/pie_chart_painter.dart

@@ -4,6 +4,7 @@ import 'package:fl_chart/fl_chart.dart';
 import 'package:fl_chart/src/chart/base/base_chart/base_chart_painter.dart';
 import 'package:fl_chart/src/chart/base/line.dart';
 import 'package:fl_chart/src/chart/pie_chart/pie_chart_data.dart';
+import 'package:fl_chart/src/extensions/paint_extension.dart';
 import 'package:fl_chart/src/utils/canvas_wrapper.dart';
 import 'package:fl_chart/src/utils/utils.dart';
 import 'package:flutter/material.dart';
@@ -102,9 +103,17 @@ class PieChartPainter extends BaseChartPainter<PieChartData> {
       final sectionDegree = sectionsAngle[i];
 
       if (sectionDegree == 360) {
+        final radius = centerRadius + section.radius / 2;
+        final rect = Rect.fromCircle(center: center, radius: radius);
         _sectionPaint
-          ..color = section.color
+          ..setColorOrGradient(
+            section.color,
+            section.gradient,
+            rect,
+          )
+          ..strokeWidth = section.radius
           ..style = PaintingStyle.fill;
+
         final bounds = Rect.fromCircle(
           center: center,
           radius: centerRadius + section.radius,
@@ -293,7 +302,11 @@ class PieChartPainter extends BaseChartPainter<PieChartData> {
     CanvasWrapper canvasWrapper,
   ) {
     _sectionPaint
-      ..color = section.color
+      ..setColorOrGradient(
+        section.color,
+        section.gradient,
+        sectionPath.getBounds(),
+      )
       ..style = PaintingStyle.fill;
     canvasWrapper.drawPath(sectionPath, _sectionPaint);
   }

repo_files/documentations/pie_chart.md

@@ -36,6 +36,7 @@ When you change the chart's state, it animates to the new state internally (usin
 |:---------------|:---------------|:-------|
 |value| value is the weight of each section, for example if all values is 25, and we have 4 section, then the sum is 100 and each section takes 1/4 of the whole circle (360/4) degree|10|
 |color| colors the section| Colors.red
+|gradient| You can use any [Gradient](https://api.flutter.dev/flutter/dart-ui/Gradient-class.html) here. such as [LinearGradient](https://api.flutter.dev/flutter/painting/LinearGradient-class.html) or [RadialGradient](https://api.flutter.dev/flutter/painting/RadialGradient-class.html)|null|
 |radius| the width radius of each section|40|
 |showTitle| determines to show or hide the titles on each section|true|
 |titleStyle| TextStyle of the titles| TextStyle(color: Colors.white, fontSize: 16, fontWeight: FontWeight.bold)|

test/chart/pie_chart/pie_chart_painter_test.dart

@@ -172,26 +172,14 @@ void main() {
       final result2 = verify(
         mockCanvasWrapper.drawCircle(
           const Offset(100, 100),
-          10 + 30 - (3 / 2),
+          10 + (3 / 2),
           captureAny,
         ),
       );
       expect(result2.callCount, 1);
       expect((result2.captured.single as Paint).color, MockData.color3);
       expect((result2.captured.single as Paint).strokeWidth, 3);
       expect((result2.captured.single as Paint).style, PaintingStyle.stroke);
-
-      final result3 = verify(
-        mockCanvasWrapper.drawCircle(
-          const Offset(100, 100),
-          10 + (3 / 2),
-          captureAny,
-        ),
-      );
-      expect(result3.callCount, 1);
-      expect((result3.captured.single as Paint).color, MockData.color3);
-      expect((result3.captured.single as Paint).strokeWidth, 3);
-      expect((result3.captured.single as Paint).style, PaintingStyle.stroke);
     });
 
     test('test 2', () {