Non Programming Manager


    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.


    npm i canvas-designer

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