react-konva

What is react-konva?

react-konva is a React wrapper for the Konva framework, which is a 2D canvas library for creating complex graphics on the web. It allows developers to use React components to draw shapes, images, and text on the canvas, making it easier to integrate with React applications.

What are react-konva's main functionalities?

Drawing Shapes

This feature allows you to draw basic shapes like rectangles and circles on the canvas. The code sample demonstrates how to create a red rectangle and a green circle using React components.

```jsx
import React from 'react';
import { Stage, Layer, Rect, Circle } from 'react-konva';

const DrawingShapes = () => (
  <Stage width={window.innerWidth} height={window.innerHeight}>
    <Layer>
      <Rect x={20} y={20} width={100} height={100} fill='red' />
      <Circle x={200} y={200} radius={50} fill='green' />
    </Layer>
  </Stage>
);

export default DrawingShapes;
```

Handling Events

This feature allows you to handle user interactions like clicks and drags. The code sample shows how to display an alert when a blue rectangle is clicked.

```jsx
import React from 'react';
import { Stage, Layer, Rect } from 'react-konva';

const HandlingEvents = () => {
  const handleClick = () => {
    alert('Rectangle clicked!');
  };

  return (
    <Stage width={window.innerWidth} height={window.innerHeight}>
      <Layer>
        <Rect x={20} y={20} width={100} height={100} fill='blue' onClick={handleClick} />
      </Layer>
    </Stage>
  );
};

export default HandlingEvents;
```

Animating Shapes

This feature allows you to animate shapes on the canvas. The code sample demonstrates how to animate a purple rectangle moving horizontally across the screen.

```jsx
import React, { useRef, useEffect } from 'react';
import { Stage, Layer, Rect } from 'react-konva';

const AnimatingShapes = () => {
  const rectRef = useRef(null);

  useEffect(() => {
    const anim = new Konva.Animation((frame) => {
      const rect = rectRef.current;
      rect.x((rect.x() + frame.timeDiff * 0.1) % window.innerWidth);
    }, rectRef.current.getLayer());
    anim.start();

    return () => anim.stop();
  }, []);

  return (
    <Stage width={window.innerWidth} height={window.innerHeight}>
      <Layer>
        <Rect ref={rectRef} x={20} y={20} width={100} height={100} fill='purple' />
      </Layer>
    </Stage>
  );
};

export default AnimatingShapes;
```

Other packages similar to react-konva

react-three-fiber

react-three-fiber is a React renderer for Three.js, a popular 3D graphics library. While react-konva focuses on 2D canvas graphics, react-three-fiber is used for creating 3D scenes and objects. It provides a similar React-based approach to managing graphics but in a 3D context.

react-canvas

react-canvas is another library for drawing graphics using React components, but it is more focused on performance and rendering large lists of items efficiently. It is less feature-rich in terms of drawing complex shapes and animations compared to react-konva.

react-svg

react-svg is a library for integrating SVG graphics into React applications. While it also deals with vector graphics, it uses SVG instead of the HTML5 canvas element. It is more suitable for static or less complex graphics compared to the dynamic and interactive capabilities of react-konva.

README

React Konva

React Konva is a JavaScript library for drawing complex canvas graphics using React.

It provides declarative and reactive bindings to the Konva Framework.

OPEN DEMO

An attempt to make React work with the HTML5 canvas library. The goal is to have similar declarative markup as normal React and to have similar data-flow model.

Currently you can use all Konva components as React components and all Konva events are supported on them in same way as normal browser events are supported.

Installation

npm install react-konva konva --save

Tutorials and Documentation

Example

import React, { Component } from 'react';
import { render } from 'react-dom';
import { Stage, Layer, Rect, Text } from 'react-konva';
import Konva from 'konva';

class ColoredRect extends React.Component {
  state = {
    color: 'green'
  };
  handleClick = () => {
    this.setState({
      color: Konva.Util.getRandomColor()
    });
  };
  render() {
    return (
      <Rect
        x={20}
        y={20}
        width={50}
        height={50}
        fill={this.state.color}
        shadowBlur={5}
        onClick={this.handleClick}
      />
    );
  }
}

class App extends Component {
  render() {
    return (
      <Stage width={window.innerWidth} height={window.innerHeight}>
        <Layer>
          <Text text="Try click on rect" />
          <ColoredRect />
        </Layer>
      </Stage>
    );
  }
}

render(<App />, document.getElementById('root'));

To get more info about Konva you can read Konva Overview.

Actually you don't need to learn react-konva. Just learn Konva framework, you will understand how to use react-konva

Comparisons

react-konva vs react-canvas

react-canvas is a completely different react plugin. It allows you to draw DOM-like objects (images, texts) on canvas element in very performant way. It is NOT about drawing graphics, but react-konva is exactly for drawing complex graphics on <canvas> element from React.

react-konva vs react-art

react-art allows you to draw graphics on a page. It also supports SVG for output. But it has no support of events of shapes.

react-konva vs vanilla canvas

Vanilla canvas is faster because when you use react-konva you have two layers of abstractions. Konva framework is on top of canvas and React is on top of Konva. Depending on the use case this approach can be slow. The purpose of react-konva is to reduce the complexity of the application and use well-known declarative way for drawing on canvas.

CHANGELOG

Note: you can find a lot of demos and examples of using Konva there: http://konvajs.github.io/. Really, just go there and take a look what Konva can do for you. You will be able to do the same with react-konva too.

Getting reference to Konva objects

To get reference of Konva instance of a node you can use ref property.

class MyShape extends React.Component {
  componentDidMount() {
    // log Konva.Circle instance
    console.log(this.circle);
  }
  render() {
    return <Circle ref={ref => (this.circle = ref)} radius={50} fill="black" />;
  }
}