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, Chat

Quick Look

<script src="https://cdn.rawgit.com/konvajs/konva/1.7.3/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);

    layer.draw();

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

Loading and installing Konva

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

1 Load Konva via classical <script> tag:

<script src="https://cdn.rawgit.com/konvajs/konva/1.7.3/konva.min.js"></script>

You can use CDN: https://cdn.rawgit.com/konvajs/konva/1.7.3/konva.min.js

2 Load via AMD (requirejs):

define(['./konva'], function(Konva) {
  // your code
});

3 CommonJS style with npm:

npm install konva --save

// old way
var Konva = require('konva');

// modern way
import Konva from 'konva';

// typescript
import * as Konva from 'konva';

4 Minimal bundle

If you are using webpack or browserfy you can use this approach to load only required Konva's parts:

import Konva from 'konva/src/Core';
// now you have Konva object with Stage, Layer, FastLayer, Group, Shape and some additional utils function
// so there are no shapes (rect, circle, etc), no filters, no d&d support.

// but you can simply add anything you need:
import 'konva/src/shapes/rect';
//now Konva.Rect is available to use

5 NodeJS

We are using node-canvas to create canvas element. Please check installation instructions for it. Then just run

npm install konva-node

Then in you javascript file you will need to use

const Konva = require('konva-node');

See file resources/nodejs-demo.js for example.

Change log

See CHANGELOG.md.

Dev environment

Before doing all dev stuff make sure you have node installed. After that, run npm install in the main directory to install the node module dependencies.

Run gulp -T to see all build options.

Building the Konva Framework

To build a development version of the framework, run gulp dev-build. To run a full build, which also produces the minified version run gulp build.

If you add a file in the src directory, be sure to add the filename to the sourceFiles array variable in gulpfile.js.

Testing

Konva uses Mocha for testing.

• If you need run test only one time run gulp test.
• While developing it is easy to use gulp default task with watch. Just run it and go to http://localhost:8080/test/runner.html. After src file change konva-dev.js will be automatically created, so you just need refresh test the page.

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 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 (gulp lint test).

Changelog

2.0.0 - 2018-03-15

Added

• new Konva.Transformer. It is a special group that allow simple resizing and rotation of a shape.
• Add ability to remove event by callback node.off('event', callback).
• new Konva.Filters.Contrast.
• new Konva.Util.haveIntersection() to detect simple collusion
• add Konva.Text.ellipsis to add '…' to text string if width is fixed and wrap is set to 'none'
• add gradients for strokes

Changed

• stage events are slightly changed. mousedown, click, mouseup, dblclick, touchstart, touchend, tap, dbltap will be triggered when clicked on empty areas too

Fixed

• Some typescript fixes
• Pixelate filter fixes
• Fixes for path data parsing
• Fixed shadow size calculation

Removed

• Some deprecated methods are removed. If previous version was working without deprecation warnings for you, this one will work fine too.