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Friday, January 27, 2023

Flutter: Drawing an N-Pointed Star with CustomClipper

This article shows you how to draw an n-pointed star (5-pointed star, 6-pointed star, 10-pointed-star, 20-pointed star, etc) by using the CustomClipper class in Flutter. There is no need to install any third-party packages. We will make things from scratch.

What Is The Point?

1. Implement a reusable custom clipper by extending the CustomClipper class:Advertisements

``````// This custom clipper help us achieve n-pointed star shape
class StarClipper extends CustomClipper<Path> {
/// The number of points of the star
final int points;
StarClipper(this.points);

// Degrees to radians conversion
double _degreeToRadian(double deg) => deg * (math.pi / 180.0);

@override
Path getClip(Size size) {
Path path = Path();
double max = 2 * math.pi;

double width = size.width;
double halfWidth = width / 2;

double wingRadius = halfWidth;
double radius = halfWidth / 2;

double degreesPerStep = _degreeToRadian(360 / points);
double halfDegreesPerStep = degreesPerStep / 2;

path.moveTo(width, halfWidth);

for (double step = 0; step < max; step += degreesPerStep) {
path.lineTo(halfWidth + wingRadius * math.cos(step),
halfWidth + wingRadius * math.sin(step));
path.lineTo(halfWidth + radius * math.cos(step + halfDegreesPerStep),
halfWidth + radius * math.sin(step + halfDegreesPerStep));
}

path.close();
return path;
}

// If the new instance represents different information than the old instance, this method will return true, otherwise it should return false.
@override
bool shouldReclip(CustomClipper<Path> oldClipper) {
StarClipper starClipper = oldClipper as StarClipper;
return points != starClipper.points;
}
}``````

2. Now you can draw a star with ease, like this:

`````` SizedBox(
height: 360,
width: 360,
child: ClipPath(
clipper: StarClipper(6),
child: Container(
height: 300,
color: Colors.amber,
),
),
),``````

The Complete Example

Preview

This example produces 4 different star shapes: a 5-pointed star, a 6-point star, a 10-pointed star, and a 20-pointed star.

The Code

The full source code in main.dart with explanations:

``````// main.dart
import 'package:flutter/material.dart';
import 'dart:math' as math;

// This custom clipper help us achieve n-pointed star shape
class StarClipper extends CustomClipper<Path> {
/// The number of points of the star
final int points;
StarClipper(this.points);

// Degrees to radians conversion
double _degreeToRadian(double deg) => deg * (math.pi / 180.0);

@override
Path getClip(Size size) {
Path path = Path();
double max = 2 * math.pi;

double width = size.width;
double halfWidth = width / 2;

double wingRadius = halfWidth;
double radius = halfWidth / 2;

double degreesPerStep = _degreeToRadian(360 / points);
double halfDegreesPerStep = degreesPerStep / 2;

path.moveTo(width, halfWidth);

for (double step = 0; step < max; step += degreesPerStep) {
path.lineTo(halfWidth + wingRadius * math.cos(step),
halfWidth + wingRadius * math.sin(step));
path.lineTo(halfWidth + radius * math.cos(step + halfDegreesPerStep),
halfWidth + radius * math.sin(step + halfDegreesPerStep));
}

path.close();
return path;
}

// If the new instance represents different information than the old instance, this method will return true, otherwise it should return false.
@override
bool shouldReclip(CustomClipper<Path> oldClipper) {
StarClipper starClipper = oldClipper as StarClipper;
return points != starClipper.points;
}
}

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

class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);

@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
title: 'KindaCode.com',
theme: ThemeData(
primarySwatch: Colors.indigo,
),
home: const MyHomePage(),
);
}
}

class MyHomePage extends StatefulWidget {
const MyHomePage({Key? key}) : super(key: key);

@override
_MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Kindacode.com'),
),
child: Center(
child: Column(
children: [
// 5-pointed star
SizedBox(
height: 180,
width: 180,
child: ClipPath(
clipper: StarClipper(5),
child: Container(
height: 150,
color: Colors.green,
),
),
),

// 6-pointed star
SizedBox(
height: 180,
width: 180,
child: ClipPath(
clipper: StarClipper(6),
child: Container(
height: 150,
color: Colors.amber,
),
),
),

// 10-pointed star
SizedBox(
height: 180,
width: 180,
child: ClipPath(
clipper: StarClipper(10),
child: Container(
height: 150,
color: Colors.indigo,
),
),
),

// 20-pointed star
SizedBox(
height: 180,
width: 180,
child: ClipPath(
clipper: StarClipper(20),
child: Container(
height: 150,
color: Colors.cyan,
),
),
),
],
),
),
),
);
}
}
``````

Conclusion

AdvertisementsWeÂ’ve drawn custom star shapes from scratch without using any 3rd plugins. If youÂ’d like to explore more new and exciting things in modern Flutter, take a look at the following articles:

You can also take a tour around our Flutter topic page and Dart topic page to see the latest tutorials and examples.Advertisements