konva

What is konva?

Konva is a 2D canvas library for JavaScript that enables developers to create complex and interactive graphics on the web. It is built on top of the HTML5 Canvas API and provides a high-level API for drawing shapes, images, text, and more. Konva is particularly useful for creating animations, interactive applications, and data visualizations.

What are konva's main functionalities?

Drawing Shapes

This feature allows you to draw various shapes such as circles, rectangles, and polygons. The code sample demonstrates how to create a stage, add a layer, and draw a red circle with a black border.

const stage = new Konva.Stage({ container: 'container', width: 500, height: 500 }); const layer = new Konva.Layer(); const circle = new Konva.Circle({ x: stage.width() / 2, y: stage.height() / 2, radius: 70, fill: 'red', stroke: 'black', strokeWidth: 4 }); layer.add(circle); stage.add(layer);

Handling Events

Konva provides an easy way to handle user interactions like clicks, mouse movements, and touch events. The code sample shows how to add a click event listener to a circle shape.

circle.on('click', function () { alert('Circle clicked!'); });

Animations

Konva supports animations, allowing you to create dynamic and interactive graphics. The code sample demonstrates how to animate a circle's position over time.

const anim = new Konva.Animation(function (frame) { circle.x(Math.sin(frame.time * 2 * Math.PI / 1000) * 100 + stage.width() / 2); }, layer); anim.start();

Transformations

You can apply transformations like scaling, rotation, and dragging to shapes. The code sample shows how to make a circle draggable and log a message during the drag event.

circle.draggable(true); circle.on('dragmove', function () { console.log('Circle is being dragged'); });

Text and Images

Konva allows you to add text and images to your canvas. The code sample demonstrates how to add a text element and an image to a layer.

const text = new Konva.Text({ x: 10, y: 10, text: 'Hello, Konva!', fontSize: 30, fontFamily: 'Calibri', fill: 'green' }); layer.add(text); const imageObj = new Image(); imageObj.onload = function () { const konvaImage = new Konva.Image({ x: 50, y: 50, image: imageObj, width: 100, height: 100 }); layer.add(konvaImage); layer.draw(); }; imageObj.src = 'path/to/image.jpg';

Other packages similar to konva

fabric

Fabric.js is a powerful and simple JavaScript HTML5 canvas library. It provides an interactive object model on top of the canvas element, making it easy to create and manipulate shapes, images, and text. Compared to Konva, Fabric.js offers more advanced features for object manipulation and is often used for applications like image editors and drawing tools.

paper

Paper.js is an open-source vector graphics scripting framework that runs on top of the HTML5 Canvas. It is designed to make it easy to work with vector graphics and bezier curves. Paper.js is more focused on vector graphics and offers a different set of tools compared to Konva, which is more general-purpose.

pixi.js

PixiJS is a fast 2D rendering engine that uses WebGL with a canvas fallback. It is designed for creating high-performance graphics and games. While Konva is more focused on ease of use and interactivity, PixiJS is optimized for performance and is often used in game development.

README

Konva

Konva is an HTML5 Canvas JavaScript framework that enables high performance animations, transitions, node nesting, layering, filtering, caching, event handling for desktop and mobile applications, and much more.

You can draw things onto the stage, add event listeners to them, move them, scale them, and rotate them independently from other shapes to support high performance animations, even if your application uses thousands of shapes. Served hot with a side of awesomeness.

This repository began as a GitHub fork of ericdrowell/KineticJS.

• Visit: The Home Page and follow on Twitter
• Discover: Tutorials, API Documentation
• Help: StackOverflow, Discord Chat

Quick Look

<script src="https://unpkg.com/konva@9/konva.min.js"></script>
<div id="container"></div>
<script>
  var stage = new Konva.Stage({
    container: 'container',
    width: window.innerWidth,
    height: window.innerHeight,
  });

  // add canvas element
  var layer = new Konva.Layer();
  stage.add(layer);

  // create shape
  var box = new Konva.Rect({
    x: 50,
    y: 50,
    width: 100,
    height: 50,
    fill: '#00D2FF',
    stroke: 'black',
    strokeWidth: 4,
    draggable: true,
  });
  layer.add(box);

  // add cursor styling
  box.on('mouseover', function () {
    document.body.style.cursor = 'pointer';
  });
  box.on('mouseout', function () {
    document.body.style.cursor = 'default';
  });
</script>

Browsers support

Konva works in all modern mobile and desktop browsers. A browser need to be capable to run javascript code from ES2015 spec. For older browsers you may need polyfills for missing functions.

At the current moment Konva doesn't work in IE11 directly. To make it work you just need to provide some polyfills such as Array.prototype.find, String.prototype.trimLeft, String.prototype.trimRight, Array.from.

Debugging

The Chrome inspector simply shows the canvas element. To see the Konva objects and their details, install the konva-dev extension at https://github.com/konvajs/konva-devtool.

Loading and installing Konva

Konva supports UMD loading. So you can use all possible variants to load the framework into your project:

Load Konva via classical <script> tag from CDN:

<script src="https://unpkg.com/konva@9/konva.min.js"></script>

Install with npm:

npm install konva --save

// The modern way (e.g. an ES6-style import for webpack, parcel)
import Konva from 'konva';

Typescript usage

Add DOM definitions into your tsconfig.json:

{
  "compilerOptions": {
    "lib": [
        "es6",
        "dom"
    ]
  }
}

3 Minimal bundle

import Konva from 'konva/lib/Core';
// Now you have a Konva object with Stage, Layer, FastLayer, Group, Shape and some additional utils function.
// Also core currently already have support for drag&drop and animations.
// BUT there are no shapes (rect, circle, etc), no filters.

// but you can simply add anything you need:
import { Rect } from 'konva/lib/shapes/Rect';
// importing a shape will automatically inject it into Konva object

var rect1 = new Rect();
// or:
var shape = new Konva.Rect();

// for filters you can use this:
import { Blur } from 'konva/lib/filters/Blur';

4 NodeJS env

In order to run konva in nodejs environment you also need to install canvas package manually. Konva will use it for 2d canvas API.

npm install konva canvas

Then you can use the same Konva API and all Konva demos will work just fine. You just don't need to use container attribute in your stage.

import Konva from 'konva';

const stage = new Konva.Stage({
  width: 500,
  height: 500,
});
// then all regular Konva code will work

Backers

• myposter GmbH
• queue.gg

Change log

See CHANGELOG.md.

Building the Konva Framework

To make a full build run npm run build. The command will compile all typescript files, combine then into one bundle and run minifier.

Testing

Konva uses Mocha for testing.

• If you need run test only one time run npm run test.
• While developing it is easy to use npm start. Just run it and go to http://localhost:1234/unit-tests.html. The watcher will rebuild the bundle on any change.

Konva is covered with hundreds of tests and well over a thousand assertions. Konva uses TDD (test driven development) which means that every new feature or bug fix is accompanied with at least one new test.

Generate documentation

Run npx gulp api which will build the documentation files and place them in the api folder.

Pull Requests

I'd be happy to review any pull requests that may better the Konva project, in particular if you have a bug fix, enhancement, or a new shape (see src/shapes for examples). Before doing so, please first make sure that all of the tests pass (npm run test).

Contributors

Financial Contributors

Become a financial contributor and help us sustain our community. [Contribute]

Individuals

Organizations

Support this project with your organization. Your logo will show up here with a link to your website. [Contribute]

Changelog

9.3.14 (2024-07-16)

• Fix shadow + corner radius for images
• Support fillRule for Konva.Shape on hit graph