feat: Add the gauge marker painter (#2096)

Author: imaNNeo

example/lib/presentation/samples/gauge/gauge_chart_sample1.dart

@@ -1,6 +1,3 @@
-import 'dart:math';
-import 'dart:ui';
-
 import 'package:fl_chart/fl_chart.dart';
 import 'package:fl_chart_app/presentation/resources/app_resources.dart';
 import 'package:flutter/material.dart';
@@ -15,6 +12,12 @@ class GaugeChartSample1 extends StatefulWidget {
 class GaugeChartSample1State extends State<GaugeChartSample1> {
   double _value = 0.5;
 
+  // Continuous min/max thresholds — deliberately off the 11-tick grid
+  // (0.0, 0.1, ..., 1.0) to show GaugeMarker carries an arbitrary
+  // value, not a discrete tick index.
+  static const _minValue = 0.23;
+  static const _maxValue = 0.77;
+
   @override
   Widget build(BuildContext context) {
     return Padding(
@@ -40,16 +43,46 @@ class GaugeChartSample1State extends State<GaugeChartSample1> {
                       position: GaugeTickPosition.center,
                       count: 11,
                       offset: 0,
-                      painter: _MyCustomGaugeMinMaxTickPainter(
+                      painter: GaugeTickCirclePainter(
                         color: AppColors.contentColorWhite,
                         radius: 5,
-                        minIndex: 2,
-                        maxIndex: 8,
-                        minMaxLineLength: 40,
-                        minMaxLineStrokeWidth: 4,
                       ),
                       checkToShowTick: GaugeTicks.hideEndpoints,
                     ),
+                    markers: const [
+                      GaugeMarker(
+                        value: _minValue,
+                        position: GaugeTickPosition.center,
+                        painter: GaugeMarkerLinePainter(
+                          length: 40,
+                          thickness: 4,
+                          color: Colors.green,
+                          label: 'Min',
+                          labelStyle: TextStyle(
+                            color: Colors.green,
+                            fontSize: 12,
+                            fontWeight: FontWeight.bold,
+                          ),
+                          labelSide: GaugeMarkerLabelSide.inward,
+                        ),
+                      ),
+                      GaugeMarker(
+                        value: _maxValue,
+                        position: GaugeTickPosition.center,
+                        painter: GaugeMarkerLinePainter(
+                          length: 40,
+                          thickness: 4,
+                          color: Colors.red,
+                          label: 'Max',
+                          labelStyle: TextStyle(
+                            color: Colors.red,
+                            fontSize: 12,
+                            fontWeight: FontWeight.bold,
+                          ),
+                          labelSide: GaugeMarkerLabelSide.inward,
+                        ),
+                      ),
+                    ],
                     pointers: [
                       // Needle extending from center toward the current value.
                       GaugePointer(
@@ -95,97 +128,3 @@ class GaugeChartSample1State extends State<GaugeChartSample1> {
     );
   }
 }
-
-class _MyCustomGaugeMinMaxTickPainter extends GaugeTickCirclePainter {
-  _MyCustomGaugeMinMaxTickPainter({
-    super.color,
-    super.radius,
-    required this.minIndex,
-    required this.maxIndex,
-    required this.minMaxLineLength,
-    required this.minMaxLineStrokeWidth,
-    this.textOffset = 6,
-    this.minTextStyle = const TextStyle(
-      color: Colors.green,
-      fontSize: 12,
-      fontWeight: FontWeight.bold,
-    ),
-    this.maxTextStyle = const TextStyle(
-      color: Colors.red,
-      fontSize: 12,
-      fontWeight: FontWeight.bold,
-    ),
-  }) : super();
-
-  final int minIndex;
-  final int maxIndex;
-  final double minMaxLineLength;
-  final double minMaxLineStrokeWidth;
-  final double textOffset;
-  final TextStyle minTextStyle;
-  final TextStyle maxTextStyle;
-
-  final _paint = Paint();
-
-  @override
-  void draw(Canvas canvas, GaugeTickInfo tickInfo) {
-    super.draw(canvas, tickInfo);
-
-    if (tickInfo.index != minIndex && tickInfo.index != maxIndex) {
-      return;
-    }
-    final isMin = tickInfo.index == minIndex;
-    final text = isMin ? "Min" : "Max";
-    final textStyle = isMin ? minTextStyle : maxTextStyle;
-    final rotation = isMin ? pi : 0.0;
-    final textPainter = TextPainter(
-      text: TextSpan(text: text, style: textStyle),
-      textDirection: TextDirection.ltr,
-    )..layout();
-    // 180 degrees
-    canvas.rotate(rotation);
-    final offsetX = isMin
-        ? 0 + textPainter.width + textOffset
-        : 0 - textPainter.width - minMaxLineLength / 2 - textOffset;
-    textPainter.paint(canvas, Offset(offsetX, 0 - textPainter.height / 2));
-    _paint.color = textStyle.color!;
-    _paint.strokeWidth = minMaxLineStrokeWidth;
-    canvas.drawLine(
-      Offset(0 - minMaxLineLength / 2, 0),
-      Offset(0 + minMaxLineLength / 2, 0),
-      _paint,
-    );
-  }
-
-  @override
-  GaugeTickPainter lerp(GaugeTickPainter b, double t) {
-    if (b is! _MyCustomGaugeMinMaxTickPainter) {
-      return b;
-    }
-    return _MyCustomGaugeMinMaxTickPainter(
-      color: Color.lerp(color, b.color, t)!,
-      radius: lerpDouble(radius, b.radius, t)!,
-      minIndex: minIndex,
-      maxIndex: maxIndex,
-      minMaxLineLength: lerpDouble(minMaxLineLength, b.minMaxLineLength, t)!,
-      minMaxLineStrokeWidth:
-      lerpDouble(minMaxLineStrokeWidth, b.minMaxLineStrokeWidth, t)!,
-      textOffset: lerpDouble(textOffset, b.textOffset, t)!,
-      minTextStyle: TextStyle.lerp(minTextStyle, b.minTextStyle, t)!,
-      maxTextStyle: TextStyle.lerp(maxTextStyle, b.maxTextStyle, t)!,
-    );
-  }
-
-  @override
-  List<Object?> get props =>
-      [
-        super.props,
-        minIndex,
-        maxIndex,
-        minMaxLineLength,
-        minMaxLineStrokeWidth,
-        textOffset,
-        minTextStyle,
-        maxTextStyle,
-      ];
-}