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A jQuery inspired canvas utility library
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gury - A jQuery inspired canvas utility library

by Ryan Sandor Richards

Gury (pronounced "jury") is a simple to use utility library for drawing, animating, and managing HTML5 canvas tags. The goal is to support the HTML5 Canvas API with a framework that allows for faster/easier application development.

It was built with simplicity in mind and its usage was modeled in the image of jQuery. For instance you can initialize, style, and animate an entire scene in a single expression using chaining.

Using gury

Getting started with Gury is a piece of cake! Here's a step-by-step guide:

  1. Create an HTML page and add a canvas with an id attribute to the body
  2. Include gury.js in a script tag
  3. Write some JavaScript to make a simple animation

To see it in action view the demo.html file in a canvas enabled browser.

Browser Compatibility

Below is the working status of Gury in various Canvas enabled browsers. If you primarily use a browser check out the demos folder and see if any of them fail. If so please raise an issue!

  • Chrome - Tested and Working (v 6.0)
  • Safari - Not tested
  • FireFox - Not tested
  • Opera - Not tested


Here is an example of some gury code to make a simple spinning square animation.

$g('screen').size(100, 100).add({
    theta: 0, 
    draw: function(ctx) {;
        ctx.translate(50, 50);
        ctx.fillStyle = "#ada";
        ctx.fillRect(-32, -32, 64, 64);
        this.theta += Math.PI / 120;

Neat, eh?

Basic Usage, Placement, and Appearance Methods

Gury(), $g()

Creates a new canvas node and returns the gury object representing that canvas.

Gury(id), $g(id)

Finds a canvas on the page with the given id and returns a gury object representing that canvas.


The canvas node represented by the gury object. Example:

$g() = "5px solid red";


The graphics context for the canvas represented by the gury object. Example:

$g().ctx.fillStyle = "#a0a";


This method is used to place canvas objects created using gury. If the node parameter is a DOM element then the canvas will be added as a child to that DOM element. If the node parameter is a string and jQuery is available the parameter is treated as a selector and the canvas is appended to the nodes returned by applying the jQuery selector.

Here's an example that places the canvas inside a node:

var container = document.getElementById('my_div');

And another that uses jQuery to place the canvas (given jQuery is loaded, of course):


*** Important *** The second example requires that you have loaded jQuery before executing the script. If jQuery is not loaded then the method will throw an exception. For more information on jQuery see

.size(width, height)

Changes the size of the canvas represented by the gury object. The parameters are expected to be in pixels. Example:

$g().size(200, 200);

which creates a new canvas and sizes it to 200px by 200px.


Changes the background style of the canvas represented by the gury object. The color parameter is expected to be a string containing the CSS for the background of the canvas. Here's an example that set's an existing canvas' background to light gray:


And another that resizes, sets the background, and finally places a canvas (this is a pretty common string of operation):

$g().size(400, 250).background('black').place('#my_div');

Object Methods


Adds an object to be rendered on the canvas. The object parameter can be either a function that accepts a single graphics context argument (for quick rendering):

$g('my_canvas').add(function(ctx) {
   ctx.fillStyle = "#f00";
   ctx.drawRect(0, 0, 20, 20);
   // ... 

or a full object that contains a draw method which accepts both the context upon which to draw and optionally a reference to the canvas node:

    x: 0, dx: 1,
    draw: function(ctx, canvas) {
        if (this.x >= canvas.width)
            this.dx *= -1;

.add(tag, object)

As with .add(object) this method adds an object to be rendered on the canvas. Additionally it associates a tag name with that object for use with the various object/tag methods described below.

A quick example:

  .add('players.mario', new Mario())
  .add('players.luigi', new Luigi())
  .toggle('players.mario'); // Luigi finally has his day!

Tags are hierarchical, meaning that if you were to then execute:


It would show the Mario object and hide the Luigi object (and Luigi would no longer rule the day, alas). For more information read the section on object tags above and see the tag methods (.each(), .hide(), etc.) below.


Removes an object from the canvas. If the object is not in the canvas then this method has no effect. Here's an example:

// Add a circle
var circle = new Circle();

// Remove that same circle

Again, remember that if you are not animating the canvas you will need to call .draw in order for the changes to appear.


Removes all objects with the given tag from the canvas. Here's an example:

// Add a box and a circle
$g('my_canvas').add('circle', new Circle()).add('box', new Box()).draw();

// Remove the box


Executes a closure on each of the objects associated with the canvas. An example explains this a bit better:

  .add(new Ball())
  .add(new Ball())
  .each(function(object, index) {
    object.x -= 10;
    object.y += 10; 

Executing the script above would move each of the objects 10 pixels down and 10 pixels to the left (note that the Ball class is not part of Gury but is used as an example).

.each(tag, closure)

Does the same thing as .each(closure) but only iterates over objects that were added with the provided tag parameter. Let's take a look with an example:

  .add('red', new Ball('red'))
  .add('red', new Ball('red'))
  .add('green', new Ball('green'))
  .each('red', function(object) {
    object.x -= 10;
    object.y += 10;

In this example only balls that were tagged with red will be moved down and to the left. All other balls (i.e. the green tagged ball) will remain unaffected.

Important: Just changing the properties of objects will not cause the canvas to redraw and display those changes. For static scenes we must explicitly redraw using the .draw() method. Animated scenes tend not to have this problem as they are technically calling .draw() on each animation interval.

Keep this in mind for .each(), .hide(), .show(), or .toggle() methods. This may change in the future, but for now it's the law of the land.

.hide() / .hide(tag)

Prevents objects from drawing and animating. Example:

  .add('circle', new Circle())
  .add('box', new Box())

The preceding example would hide all objects regardless of their tag. Here's another example:

  .add('circle', new Circle())
  .add('box', new Box())

which hides only the circle, leaving the box rendering alone (poor lonely box). Again, as with many of these examples, the Box and Circle classes aren't part of Gury but are used as examples.

.show() / .show(tag)

Ensures that objects render and animate. Example:

  .add('box', new Box())

// ... Maybe do some other stuff ...


In the preceding example we created a box, immediately hid it, and then turned around and decided to show everything anyway. While not practical (or particularly sane) it is illustrative of using .show(). The next example uses tags:

  .add('box', new Box())
  .add('circle', new Circle)

In this example we add a box, then a circle, then hide everything, and finally show only the circle by using tags.

.toggle() / .toggle(tag)

What visibility library would be complete without a toggle method? This method basically just toggles objects on and off as it is called. Let's get going with an example:

var gury = $g('my_canvas')
  .add('box', new Box())
  .add('circle', new Circle()).play(16);

// Add a little jQuery action...
$('#my_button').click(function() {

The example above simply adds a box and a circle and then uses some jQuery magic to bind an event that toggles all of the objects on and off when some element with the id my_button is clicked. A final example should cement the concept:

  .add('box', new Box())
  .add('circle', new Circle())

Simple enough: we just add a box, a circle, then toggle the box off and draw the scene.

Drawing and Animation Methods


Renders the scene by drawing all of the added objects in order on the canvas.


Updates objects that have a .update() method. This method is called before .draw() for animations via the .play() method. This allows for you to separate out your update and rendering code and ensure updates have been performed before they are rendered to the screen. Here is a quick example:

$g('my_canvas').size(64, 64).add({
    theta: 0,
    update: function() {
        this.theta += Math.PI / 60;
    draw: function() {;
            ctx.translate(64, 64);
            ctx.fillStyle = 'red';
            ctx.fillRect(-16, -16, 32, 32);

The demos/tags.html uses this functionality extensively.


Clears the canvas (does not remove any objects bound to the Gury instance).


Renders the scene repeatedly at fixed intervals creating an animation. This is most useful when used in conjunction with objects that change state on render. See demos/demo1.html and demos/demo3.html for examples of objects that change position or rotation on the screen as the animation plays.


Toggles updates and rendering for the canvas itself. Individually paused objects will not be toggled back into motion by calling .pause() with no arguments. For more on pausing objects see .pause(object) and .pause(tag) below.


Toggles updates for a single object in the canvas. See demos/pausing.html for an example of how to use this.


Toggles updates for all objects with the given tag. Again, see demos/pausing.html for an example of how to use this.


Fully stops the gury animation. You must call play() in order to start the animation again after calling stop().

Module Methods


Returns true if Gury fails with an exception, and returns false if Gury actions fail silently. By default it will return true (which is recommended for development, but maybe not for production).


Allows you to set whether or not Gury will fail silently or with an exception. Just set the b parameter to false if you do not want to see failure exceptions and to true if you do.

A Note on Objects and Canvas Tags

Each object you add to the display list using Gury will be annotated with a special property named ._gury. Essentially it holds information about the object with respect to the canvas it is to be displayed on (a good example is the object's visibility status, used by .toggle() et. al.). This is true of both objects and functions that are added using the .add() method.

WARNING If you alter or replace the ._gury property of an object it may break some basic internal functionality (such as hiding/showing, etc.).

Additionally canvas tags that are associated with or created by Gury will also be annotated with a special property named ._gury_id. This allows Gury to ensure a persistent state between multiple calls to the $g() method.

WARNING If you alter or replace the ._gury_id property of your canvas tags you could break the internal functionality for pretty much all methods, lose objects, or even cause unsightly memory leaks (no amount of coding cosmetics can save you from a memory leak blemish, just ask any C programmer).

License (MIT)

Copyright (c) 2010 Ryan Sandor Richards

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.


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