Home > Articles > Web Development > HTML/CSS

Top 10 HTML5 Canvas Features

The advent of the Canvas 2D API dramatically expands the capabilities of HTML5 Canvas. David Geary, author of Core HTML5 Canvas: Graphics, Animation, and Game Development, shares his excitement about the new options available to application designers, presenting a 'top 10' list of the best improvements and expansions in this hardworking tool of the trade.
Like this article? We recommend

The canvas element is arguably the single most exciting aspect of HTML5. Initially implemented by Apple for Dashboard widgets on Mac OS X and adopted as a standard by the Web Hypertext Application Technology Working Group (WHATWG) in 2005, canvas is a scriptable bitmap that lets you implement all sorts of interesting applications such as data visualization and video games that were never before possible with HTML, JavaScript, and CSS.

Using the canvas tag is straightforward: You put it in your HTML, like this:

<!DOCTYPE html>
         Your browser does not support HTML5 Canvas

The text inside the canvas element is known as fallback content, meaning content the browser "falls back" (reverts) to when it doesn't support HTML5 Canvas. As one of the earliest additions to the HTML 5 specification, Canvas is widely supported among browser vendors, so it's likely that the fallback content in your canvas elements will never be displayed.

You access the canvas element and its underlying 2D graphics context like this:

var canvas = document.getElementById('game-canvas'),
   context = canvas.getContext('2d'), // Note: It's '2d', not '2D'

The preceding JavaScript obtains a reference to the canvas element. That element is merely a container for a graphics context that the preceding code accesses through the canvas getContext() method. There is also a 3D context, commonly known as WebGL, which is more powerful than the 2D context, but it comes with a much steeper learning curve and an obtuse application programming interface (API). For 2D graphics, the 2D context, which is the topic of this article, is typically a better choice than WebGL.

The 2D context provides more than 30 methods that let you do everything from drawing graphics primitives (such as lines and rectangles) to manipulating the individual bits of a particular image. For example, you could draw a filled rectangle 100 pixels wide by 100 pixels high at (10, 10) like this:

context.fillStyle = 'rgba(200, 200, 200, 0.5)'; // semi-transparent light gray
context.fillRect(10, 10, 100, 100); // (x, y, w, h)

When most people think of Canvas, they typically think of 2D games, and for good reason. Canvas has always had a solid API for implementing games, and with the advent of hardware acceleration, Canvas is well suited for implementing high-octane video games.

You can use the Canvas 2D context API for a lot more than just video games, however. In the rest of this article, I'll discuss what I consider to be the top 10 features of that API:

  1. New functionality in the 2D API
  2. The clipping region
  3. Drawing images and more with drawImage()
  4. Image manipulation
  5. Transforming the coordinate system
  6. Offscreen canvases
  7. Temporary drawing
  8. canvas is an HTML element
  9. Hit detection
  10. Path-based graphics and the nonzero winding rule

Feature #10: Path-Based Graphics and the Nonzero Winding Rule

Like scalable vector graphics, Apple's Cocoa, and Adobe's Illustrator, the Canvas 2D API is path-based. To draw graphics primitives, such as lines, rectangles, and arcs, you create a path—which is just a sequence of points—and then stroke or fill that path.

A single path can contain multiple subpaths; for example, the application shown in Figure 1 draws the cutouts from a single path—the rectangle enclosing the cutouts—that contains paths for the small rectangle, triangle, and circle.

Figure 1 Drawing cutouts.

Here's an excerpt of the code that draws the cutouts for the application in Figure 1:

function drawCutouts() {
   addOuterRectanglePath(); // clockwise

   addCirclePath();      // counter-clockwise
   addRectanglePath();   // counter-clockwise
   addTrianglePath();    // counter-clockwise

   context.fill(); // Cut out shapes

function addOuterRectanglePath() {
   context.rect(110, 25, 370, 335);

function addCirclePath() {
   context.arc(300, 300, 40, 0, Math.PI*2, true);

function addRectanglePath() {
   rect(310, 55, 70, 35, true);

function addTrianglePath() {
   context.moveTo(400, 200);
   context.lineTo(250, 115);
   context.lineTo(200, 200);

function rect(x, y, w, h, direction) {
  if (direction) { // counter-clockwise
      context.moveTo(x, y);
      context.lineTo(x, y + h);
      context.lineTo(x + w, y + h);
      context.lineTo(x + w, y);
  else {
      context.moveTo(x, y);
      context.lineTo(x + w, y);
      context.lineTo(x + w, y + h);
      context.lineTo(x, y + h);

The preceding code uses the following 2D context methods to create paths: moveTo(), lineTo(), rect(), and arc(). Then it uses fill() to fill the path.

The more interesting aspect of the preceding code, however, is its use of the nonzero winding rule to create the cutout effect. When a path's subpaths intersect or overlap, as is the case in the preceding application, the context must determine which areas to fill when the fill() method is invoked. For that, the context uses the nonzero winding rule, which uses a path's direction to determine what areas to fill.

With Canvas, you can create a complex path, possibly containing subpaths, out of regular or irregular shapes, and then you can stroke or fill that path, or use the path for other purposes. For example, you specify the clipping region of the Canvas (feature #2 in our countdown), with a path.

Paths are an important Canvas feature, and are even more powerful in the latest version of the Canvas specification. (I discuss the latest changes in the section "Feature #1: New Functionality in the 2D API," at the end of this article.)

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020