catmull_rom_spline_curve 1.0.1

A new Flutter package to help drawing Curves using Catmull-Rom Interpolation.

example/example.dart

// ignore_for_file: prefer_const_constructors

import 'dart:ui';
import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Curve',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Curve Test'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Center(
        child: SizedBox(
          width: 200,
          height: 200,
          child: CatmullCurve.drawCurve(
            [
              Offset(0, 200),
              Offset(20, 50),
              Offset(30, 200),
            ],
            Colors.red,
            2,
            PaintingStyle.stroke,
            pointcolor: Colors.blue,
            drawPoints: true,
            pointsStrokeWidth: 8,
          ),
        ),
      ),
    );
  }
}

class CatmullCurve {
  static CustomPaint drawCurve(
      List<Offset> points, Color color, double strokeWidth, PaintingStyle style,
      {bool drawPoints = false, double? pointsStrokeWidth, Color? pointcolor}) {
    return CustomPaint(
        painter: CurvePainter(
            points: points,
            color: color,
            strokeWidth: strokeWidth,
            style: style,
            drawPoints: drawPoints,
            pointcolor: pointcolor ?? Colors.red,
            pointsStrokeWidth: pointsStrokeWidth ?? strokeWidth * 2));
  }
}

class CurvePainter extends CustomPainter {
  final List<Offset> points;

  final Color color;
  final Color pointcolor;
  final double strokeWidth;
  final PaintingStyle style;
  final bool drawPoints;
  final double pointsStrokeWidth;

  CurvePainter({
    super.repaint,
    required this.points,
    required this.color,
    required this.pointcolor,
    required this.strokeWidth,
    required this.style,
    required this.drawPoints,
    required this.pointsStrokeWidth,
  });

  @override
  void paint(Canvas canvas, Size size) {
    final path = Path();

    for (int i = 0; i < points.length - 1; i++) {
      Offset p1;
      Offset p2;
      Offset p3;

      Offset p1Spline;
      Offset p2Spline;
      Offset p3Spline;
      Offset p4Spline;
      if (points.length < 3) {
        p1 = points[i];
        p2 = points[i + 1];
        p3 = points[i];
        p1Spline = p1;
        p2Spline = p1;
        p3Spline = p2;
        p4Spline = p2;
      } else if (i == 0) {
        p1 = points[i];
        p2 = points[i + 1];
        p3 = points[i + 2];
        p1Spline = p1;
        p2Spline = p1 - ((p1 - p2) / 6);
        p3Spline = p2 - ((p3 - p1) / 6);
        p4Spline = p2;
      } else if (i == points.length - 1) {
        p1 = points[i - 1];
        p2 = points[i];
        p3 = points[i + 1];
        p1Spline = p2;
        p2Spline = p2 + ((p2 - p1) / 6);
        p3Spline = p3 - ((p3 - p2) / 6);
        p4Spline = p3;
      } else {
        p1 = points[i - 1];
        p2 = points[i];
        p3 = points[i + 1];
        p1Spline = p2;
        p2Spline = p2 + ((p2 - p1) / 6);
        p3Spline = p3 - ((p3 - p1) / 6);
        p4Spline = p3;
      }

      final paint = Paint();
      paint.color = color;
      paint.strokeWidth = strokeWidth;
      paint.style = style;

      final pointsPaint = Paint();
      pointsPaint.color = pointcolor;
      pointsPaint.strokeWidth = pointsStrokeWidth;
      pointsPaint.style = style;
      pointsPaint.strokeCap = StrokeCap.round;

      path.moveTo(p1Spline.dx, p1Spline.dy);
      path.cubicTo(p2Spline.dx, p2Spline.dy, p3Spline.dx, p3Spline.dy,
          p4Spline.dx, p4Spline.dy);

      canvas.drawPath(path, paint);
      if (drawPoints == true) {
        canvas.drawPoints(PointMode.points, points, pointsPaint);
      }
    }
  }

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