1.3.0 • Public • Published

Canvas Designer / API Referencee


Advance Demo: demos/dashboard/

Multiple designers demo:

YouTube video:

npm downloads Build Status: Linux

"Collaborative" Canvas Designer i.e. Canvas-Drawing tool allows you draw bezier/quadratic curves, rectangles, circles and lines. You can also set strokes, back/forth colors and much more. You can draw using pencils, erase drawing, type texts etc. You can easily add your own tools.

You can check all releases here:

The specialty of this drawing-tool is that, it generates Canvas2D code for you; so simply draw and get the code! That code can be used in any javascript Canvas2D application.

You can submit issues here:

Also, you can collaborate your drawing with up to 15 users; and everything is synced from all users. So, if you draw a line and your friend-A draws quadratic curve and friend-B draws rectangle then everything will be synced among all users!

Youtube Videos

Gif images:

Built-in tools

You can use designer.setSelected or designer.setTools for below tools.

  1. line --- to draw straight lines
  2. pencil --- to write/draw shapes
  3. dragSingle --- to drag/ove and especially resize last selected shape
  4. dragMultiple --- to drag/move all shapes
  5. eraser --- to erase/clear specific portion of shapes
  6. rectangle --- to draw rectangles
  7. arc --- to draw circles
  8. bezier --- to draw bezier curves
  9. quadratic --- to draw quadratic curves
  10. text --- to write texts on single or multiple lines, select font families/sizes and more
  11. image --- add external images
  12. arrow --- draw arrow lines
  13. marker --- draw markers
  14. lineWidth --- set line width
  15. colorsPicker --- background and foreground colors picker
  16. extraOptions --- extra options eg. lineCap, lineJoin, globalAlpha, globalCompositeOperation etc.
  17. pdf --- to import PDF
  18. code --- to enable/disable code view
  19. undo --- undo recent shapes

The correct name for dragSingle should be: drag-move-resize last-selected-shape.

The correct name for dragMultiple should be: drag-move all-shapes.

Upcoming tools

  1. Allow users to add video-streams or screen-streams or existing-webm-mp4-videos
  2. Resize all shapes at once (currently you can resize last selected shape only)


  1. Draw single or multiple shapes of any kind (according to toolbox)

  2. Drag/resize/adjust all the shapes in any possible direction

  3. Rectangles and images can be resized in 4-directions

    Red transparent small circles helps you understand how to resize.

  4. Undo drawings using ctrl+z keys (undo all shapes, undo last 10 or specific shapes, undo range of shapes or undo last shape)

  5. Drag/move single or all the shapes without affecting any single coordinate

More importantly, you can use unlimited designers on a single page. Each will have its own surface and its own tools.

Chinese, Arabic, other languages

You can install following chrome extension for multi-language input tools:

Now type your own language text in any <input> box or anywhere, and simply copy that text.

Now click T tool icon from the tool-box and press ctrl+v to paste your own language's text.

To repeat it:

  1. Type your own language texts anywhere and make sure to copy to clipboard using ctrl+v
  2. Then click T icon, and then press ctrl+v to paste your copied text

You can paste any text: English, Arabic, Chinese etc.

How to Use

  1. Download/link canvas-designer-widget.js from this github repository.

  2. Set designer.widgetHtmlURL and designer.widgetJsURL in your HTML file.

  3. Use this command to append widget in your HTML page:

    var designer = new CanvasDesigner();


<!-- 1st step -->
<script src=""></script>
<!-- 2nd step -->
var designer = new CanvasDesigner();
// both links are mandatory
// widget.html will internally use widget.js
designer.widgetHtmlURL = ''; // you can place this file anywhere
designer.widgetJsURL = '';     // you can place this file anywhere
<!-- 3rd i.e. last step -->
// <iframe> will be appended to "document.body"
designer.appendTo(document.body || document.documentElement);

You can even download TAR:

mkdir Canvas-Designer && cd Canvas-Designer
tar -zxvf canvas-designer.tar.gz
ls -a

Complete Usage

var designer = new CanvasDesigner();
websocket.onmessage = function(event) {
    designer.syncData( JSON.parse( );
designer.addSyncListener(function(data) {
    pencil: true,
    text: true

It is having designer.destroy() method as well.

Use WebRTC!

webrtc.onmessage = function(event) {
    designer.syncData( );
designer.addSyncListener(function(data) {


socket.on('message', function(data) {
    designer.syncData( data );
designer.addSyncListener(function(data) {
    socket.emit('message', data);

API Reference


You can place widget.html file anywhere on your site.

designer.widgetHtmlURL = '/html-files/widget.html';

By default widget.html is placed in the same directory of index.html.

// here is default value
designer.widgetHtmlURL = 'widget.html';

Remember, widget.html is loaded using <iframe>.


Note: This file is internally used by widget.html.

You can place widget.html file anywhere on your site.

designer.widgetJsURL = '/js-files/widget.min.js';

By default widget.min.js is placed in the same directory of index.html.

// here is default value
designer.widgetJsURL = 'widget.min.js';

Remember, widget.js is loaded using <iframe>.


Pass array-of-points that are shared by remote users using or websockets or XMPP or WebRTC.



Remove and clear all drawings from the canvas:



Call this method internally to fix video rendering issues.



This callback is invoked as soon as something new is drawn. An array-of-points is passed over this function. That array MUST be shared with remote users for collaboration.

designer.addSyncListener(function(data) {


This method allows you select specific tools.



This method allows you choose between tools that should be displayed in the tools-panel.

    line: true,
    arrow: true,
    pencil: true,
    marker: true,
    dragSingle: true,
    dragMultiple: true,
    eraser: true,
    rectangle: true,
    arc: true,
    bezier: true,
    quadratic: true,
    text: true,
    image: true,
    pdf: true,
    zoom: true,
    lineWidth: true,
    colorsPicker: true,
    extraOptions: true,
    code: true,
    undo: true


You can force/set your own tool-icons:

designer.icons = {
    line: '/icons/line.png',
    arrow: '/icons/arrow.png',
    pencil: '/icons/pencil.png',
    dragSingle: '/icons/dragSingle.png',
    dragMultiple: '/icons/dragMultiple.png',
    eraser: '/icons/eraser.png',
    rectangle: '/icons/rectangle.png',
    arc: '/icons/arc.png',
    bezier: '/icons/bezier.png',
    quadratic: '/icons/quadratic.png',
    text: '/icons/text.png',
    image: '/icons/image.png',
    pdf: '/icons/pdf.png',
    pdf_next: '/icons/pdf-next.png',
    pdf_prev: '/icons/pdf-prev.png',
    marker: '/icons/marker.png',
    zoom: '/icons/zoom.png',
    lineWidth: '/icons/lineWidth.png',
    colorsPicker: '/icons/colorsPicker.png',
    extraOptions: '/icons/extraOptions.png',
    code: '/icons/code.png'

You can set like this as well:

designer.icons.line = '/icons/line.png';

Default values are NULL to force icons from /dev/data-dris.js.


CanvasDesigner is a widget; that widget should be appended to a DOM object. This method allows you pass <body> or any other HTMLDOMElement.

designer.appendTo(document.body || document.documentElement);
// or
designer.appendTo(document.body || document.documentElement, function() {
    alert('iframe load callback');

The correct name for appendTo is: append-iframe to target HTML-DOM-element


If you want to remove the widget from your HTMLDOMElement.



You can access designer iframe as following: = '5px solid red';;

designer.iframe will be null/undefined until you call appendTo. So always use this code-block:

if(!designer.iframe) {
} = '5px solid red';


Get data-URL of your drawings!

designer.toDataURL('image/png', function(dataURL) {;


You can manually sync drawings by invoking designer.sync method:


Here is a real usecase:

webrtcDataChannel.onopen = function() {
    if(designer.pointsLength > 0) {
        // you seems having data to be synced with new user!


Get MediaStream object and share in realtime using RTCPeerConnection.addStream API.

<script src="dev/webrtc-handler.js"></script>
designer.captureStream(function(stream) {
    var url = URL.createObjectURL(stream);
    videoPreview.src = url;
    rtcPeerConnection.createOffer(success, failure, params);


Each shape is considered as a point. This value allows you check number of shapes that are already drawn on the canvas-designer.

(function looper() {
    document.getElementById('number-of-shapes').inenrHTML = designer.pointsLength;
    setTimeout(looper, 1000);

Or a real usage:

websocket.onopen = function() {
    if(designer.pointsLength > 0) {
        // you seems having data to be synced with existing users!


You can either undo drawings by pressing ctrl+z on windows and command+z on Mac; however you can undo using designer.undo method as well:

designer.undo();   // undo last shape
designer.undo(-1); // undo last shape
// undo shape from specific index
// undo all shapes
// undo last 10 shapes
    numberOfLastShapes: 10

designer.pointsLength shows number of shapes; and designer.undo accepts shape-index as well.

Add New Tools

First Step

Open widget.html and add your new tool-icon HTML.

<div id="tool-box" class="tool-box"> <!-- search for this div; and include your HTML inside this div -->
    <canvas id="yourNewToolIcon" width="40" height="40"></canvas> <!-- here is your icon-HTML -->

Second Step

Open decorator.js and decorate your new HTML icon.

var tools = {
    yourNewToolIcon: true // add this line to make sure index.html can use it

Search for decorateLine method, and append following snippet quickly after that method:

function decorateYourNewToolIcon() {
    var context = getContext('yourNewToolIcon');
    context.fillStyle = 'Gray';
    context.font = '9px Verdana';
    context.fillText('New', 16, 12);
    bindEvent(context, 'YourNewToolIconSelected');
if (tools.yourNewToolIcon === true) {
} else document.getElementById('yourNewToolIcon').style.display = 'none';

Third Step

Open common.js and add selection-states for your new tool-icon (i.e. whether your new tool icon is selected or not):

var is = {
    isYourNewToolIconSelected: false, // add this line
    set: function (shape) {
        var cache = this;
        cache.isYourNewToolIconSelected = false; // add this line as well.
        // ..... don't modify anything else
        cache['is' + shape] = true;

You merely need to set isYourNewToolIconSelected:true also cache.isYourNewToolIconSelected=false.

Fourth Step

Create new file in the dev directory. Name this file as yourNewToolIcon-handler.js.

This file MUST look like this:

var yourNewToolIconHandler = {
    ismousedown: false,
    mousedown: function(e) {
        this.ismousedown = true;
    mouseup: function(e) {
        this.ismousedown = false;
    mousemove: function(e) {
        if(this.ismousedown) { ... }

You can check other *-handler.js from dev directory to get the idea how exactly it works.

Now open Gruntfile.js#L43 and add link to your new file: dev/events-handler.js.

Now compile all your changes using grunt.

Fifth Step

Open events-handler.js and make sure that your above yourNewToolIconHandler object is called for mouse up/down/move events.

addEvent(canvas, isTouch ? 'touchstart' : 'mousedown', function (e) {
    // you merely need to add this line at the end of this method
    else if (is.isYourNewToolIconSelected) yourNewToolIconHandler.mousedown(e);
addEvent(document, isTouch ? 'touchend' : 'mouseup', function (e) {
    // you merely need to add this line at the end of this method
    else if (is.isYourNewToolIconSelected) yourNewToolIconHandler.mouseup(e);
addEvent(canvas, isTouch ? 'touchmove' : 'mousemove', function (e) {
    // you merely need to add this line at the end of this method
    else if (is.isYourNewToolIconSelected) yourNewToolIconHandler.mousemove(e);

First of all, we are checking whether your tool-icon is selected or not: is.isYourNewToolIconSelected

Then we are calling yourNewToolIconHandler dot mousedown/mouseup/mousemove events respectively.

Sixth Step

Open draw-helper.js. Make sure that your new tool-icon can be drawn on the <canvas> surface.

yourNewToolIcon: function(context, point, options) {
    context.moveTo(point[0], point[1]);
    context.whateverYouWantToDoHere(point[2], point[3]);
    this.handleOptions(context, options);

Usually point[0] is x coordinates; point[1] is y coordinates; point[2] is width and point[3] is height.

Different shapes can handle these points differently.

There is NO-limit for point[index]. You can add as many points as you want.

Complex shapes can add 10 or 20 points.

Seventh Step

Open drag-helper.js and make sure that your new shape can be dragged/resized/move.

Search for p[0] === 'line' and add similar code-blocks for your shape (new-tool-icon) as well.

Eighth Step

Open common.js and make sure that your new shape (tool-icon) is printed on the <textarea> as well.

This allows end-users to copy your shape's code and use anywhere on their own web-pages.

Open common.js file; there is a function updateTextArea inside the "common" object – which is aimed to output into textarea element.

You don't have to change updateTextArea. For simplicity purpose, code is separated in different functions/properties that you've to edit:

  1. forLoop
  2. absoluteNOTShortened
  3. relativeShortened
  4. relativeNOTShortened

Search for p[0] === 'line' and add similar code-blocks for your shape (new-tool-icon) as well.

For more information

Shortcut Keys

ctrl+t (to display text-fonts box)
ctrl+z (to undo last-single shape)
ctrl+a (to select all shapes)
ctrl+c (copy last-selected shape)
ctrl+v (paste last-copied shape)

ctrl+mousedown allows you quickly copy/paste all shapes. (i.e. ctrl button + mouse down)

Signaling Server

You need only these two files:

  1. server.js
  2. Signaling-Server.js

You also need to manually install

npm install --save-dev
node server --port=9002 --ssl --ssl_key=/home/ssl/ssl.key --ssl_cert=/home/ssl/ssl.crt

For more info:


  1. Muaz Khan
  2. Oleg Aliullov

Please make pull-request to update this list.


Canvas Designer is released under MIT licence . Copyright (c) Muaz Khan.


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