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HTML5 Canvas

Cover of HTML5 Canvas by Steve Fulton... Published by O'Reilly Media, Inc.
  1. HTML5 Canvas
    1. SPECIAL OFFER: Upgrade this ebook with O’Reilly
    2. A Note Regarding Supplemental Files
    3. Preface
      1. Running the Examples in the Book
      2. What You Need to Know
      3. How This Book Is Organized
      4. Conventions Used in This Book
      5. Using Code Examples
      6. We’d Like to Hear from You
      7. Safari® Books Online
      8. Acknowledgments
    4. 1. Introduction to HTML5 Canvas
      1. The Basic HTML Page
      2. Basic HTML We Will Use in This Book
      3. The Document Object Model (DOM) and Canvas
      4. JavaScript and Canvas
      5. HTML5 Canvas “Hello World!”
      6. Debugging with Console.log
      7. The 2D Context and the Current State
      8. The HTML5 Canvas Object
      9. Another Example: Guess The Letter
      10. What’s Next
    5. 2. Drawing on the Canvas
      1. The Basic File Setup for This Chapter
      2. The Basic Rectangle Shape
      3. The Canvas State
      4. Using Paths to Create Lines
      5. Advanced Path Methods
      6. Compositing on the Canvas
      7. Simple Canvas Transformations
      8. Filling Objects with Colors and Gradients
      9. Filling Shapes with Patterns
      10. Creating Shadows on Canvas Shapes
      11. What’s Next
    6. 3. The HTML5 Canvas Text API
      1. Displaying Basic Text
      2. Setting the Text Font
      3. Text and the Canvas Context
      4. Text with Gradients and Patterns
      5. Width, Height, Scale, and toDataURL() Revisited
      6. Final Version of Text Arranger
      7. What’s Next
    7. 4. Images on the Canvas
      1. The Basic File Setup for This Chapter
      2. Image Basics
      3. Simple Cell-Based Sprite Animation
      4. Advanced Cell-Based Animation
      5. Applying Rotation Transformations to an Image
      6. Creating a Grid of Tiles
      7. Zooming and Panning an Image
      8. Pixel Manipulation
      9. Copying from One Canvas to Another
      10. What’s Next
    8. 5. Math, Physics, and Animation
      1. Moving in a Straight Line
      2. Bouncing Off Walls
      3. Curve and Circular Movement
      4. Simple Gravity, Elasticity, and Friction
      5. Easing
      6. What’s Next?
    9. 6. Mixing HTML5 Video and Canvas
      1. HTML5 Video Support
      2. Converting Video Formats
      3. Basic HTML5 Video Implementation
      4. Preloading Video in JavaScript
      5. Video and the Canvas
      6. Video on the Canvas Examples
      7. Animation Revisited: Moving Videos
      8. What’s Next?
    10. 7. Working with Audio
      1. The Basic <audio> Tag
      2. Audio Formats
      3. Audio Tag Properties, Functions, and Events
      4. Playing a Sound with No Audio Tag
      5. Creating a Canvas Audio Player
      6. Case Study in Audio: Space Raiders Game
      7. What’s Next
    11. 8. Canvas Game Essentials
      1. Why Games in HTML5?
      2. Our Basic Game HTML5 File
      3. Our Game’s Design
      4. Game Graphics: Drawing with Paths
      5. Animating on the Canvas
      6. Applying Transformations to Game Graphics
      7. Game Graphic Transformations
      8. Game Object Physics and Animation
      9. A Basic Game Framework
      10. Putting It All Together
      11. The player Object
      12. Geo Blaster Game Algorithms
      13. The Geo Blaster Basic Full Source
      14. Rock Object Prototype
      15. What’s Next
    12. 9. Combining Bitmaps and Sound
      1. Geo Blaster Extended
      2. Creating a Dynamic Tile Sheet at Runtime
      3. A Simple Tile-Based Game
      4. What’s Next
    13. 10. Mobilizing Games with PhoneGap
      1. Going Mobile!
      2. Creating the iOS Application with PhoneGap
      3. Beyond the Canvas
      4. What’s Next
    14. 11. Further Explorations
      1. 3D with WebGL
      2. Multiplayer Applications with ElectroServer 5
      3. Conclusion
    15. Index
    16. About the Authors
    17. Colophon
    18. SPECIAL OFFER: Upgrade this ebook with O’Reilly
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Chapter 1. Introduction to HTML5 Canvas

HTML5 is the current iteration of HTML, the HyperText Markup Language. HTML was first standardized in 1993, and it was the fuel that ignited the World Wide Web. HTML is a way to define the contents of a web page using tags that appear within pointy brackets, < >.

HTML5 Canvas is an immediate mode bitmapped area of the screen that can be manipulated with JavaScript. Immediate mode refers to the way the canvas renders pixels on the screen. HTML5 Canvas completely redraws the bitmapped screen on every frame using Canvas API calls from JavaScript. As a programmer, your job is to set up the screen display before each frame is rendered so that the correct pixels will be shown.

This makes HTML5 Canvas very different from Flash, Silverlight, or SVG, which operate in retained mode. In this mode, a display list of objects is kept by the graphics renderer, and objects are displayed on the screen according to attributes set in code (i.e., the x position, y position, and alpha transparency of an object). This keeps the programmer away from low-level operations, but gives her less control over the final rendering of the bitmapped screen.

The basic HTML5 Canvas API includes a 2D context that allows a programmer to draw various shapes, render text, and display images directly onto a defined area of the browser window. You can apply colors; rotations; alpha transparencies; pixel manipulations; and various types of lines, curves, boxes, and fills to augment the shapes, text, and images you place onto the canvas.

In itself, the HTML5 Canvas 2D context is a display API used to render graphics on a bitmapped area, but there is very little in that context to create applications using the technology. By adding cross-browser-compatible JavaScript functionality for keyboard and mouse inputs, timer intervals, events, objects, classes, sound, math functions, etc., you can learn to take HTML5 Canvas and create stunning animations, applications, and games.

Here’s where this book comes in. We are going to break down the Canvas API into digestible parts and then put it back together, demonstrating how to use it to create applications. Many of the techniques you will learn in this book have been tried and used successfully on other platforms, and now we are applying them to this exciting new technology.

The Basic HTML Page

Before we get to Canvas, we need to talk a bit about the HTML5 standards we will be using to create our web pages.

HTML is the standard language used to construct pages on the World Wide Web. We will not spend much time on HTML, but it does form the basis of <canvas>, so we cannot skip it entirely.

A basic HTML page is divided into sections, commonly <head> and <body>. The new HTML5 specification adds a few new sections, such as <nav>, <article>, <header>, and <footer>.

The <head> tag usually contains information that will be used by the HTML <body> tags to create the HTML page. It is a standard convention to put JavaScript functions in the <head>, as you will see later when we discuss the <canvas> tag. There may be reasons to put some JavaScript in the <body>, but we will make every attempt to keep things simple by having all JavaScript in the <head>.

Basic HTML for a page might look like Example 1-1.

Example 1-1. A basic HTML page

<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>CH1EX1: Basic Hello World HTML Page</title>
</head>
<body>
Hello World!
</body>
</html>

<!doctype html>

This tag informs the web browser to render the page in standards mode. According to the HTML5 spec from W3C, this is required for HTML5 documents. This tag simplifies a long history of oddities when it came to rendering HTML in different browsers. This should always be the first line of HTML in a document.

<html lang="en">

This is the <html> tag with the language referenced: for example, “en” = English. Some of the more common language values are:

Chinese – lang = “zh”
French – lang = “fr”
German – lang = “de”
Italian – lang = “it”
Japanese – lang = “ja”
Korean – lang = “ko”
Polish – lang = “pl”
Russian – lang = “ru”
Spanish (Castilian) – lang = “es”

<meta charset="UTF-8">

This tag tells the web browser which character-encoding method to use for the page. Unless you know what you’re doing, there is no need to change it. This is a required element for HTML5 pages.

<title>…</title>

This is the title that will be displayed in the browser window for the HTML page. This is a very important tag, as it is one of the main pieces of information a search engine uses to catalog the content on the HTML page.

A Simple HTML5 Page

Now let’s look at this page in a web browser (this would be a great time to get your tools together to start developing code). Open your chosen text editor, and get ready to use your preferred web browser: Safari, Firefox, Opera, Chrome, or IE.

  1. In your text editor, type in the code from Example 1-1.

  2. Save the code as CH1EX1.html in a directory of your choosing.

  3. Under the File menu in Chrome, Safari, or Firefox, you should find the option Open File. Click that selection. You should then see a box to open a file. (On Windows using Chrome, you might need to press Ctrl+O to open a file.)

  4. Locate the CH1EX1.html that you just created.

  5. Click Open.

You should see something similar to Figure 1-1.

HTML Hello World!

Figure 1-1. HTML Hello World!

Warning

This is one of only two examples in this entire book that will work with Internet Explorer 8 or earlier.

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