Book Image

HTML5 Canvas Cookbook

By : Eric Rowell
Book Image

HTML5 Canvas Cookbook

By: Eric Rowell

Overview of this book

The HTML5 canvas is revolutionizing graphics and visualizations on the Web. Powered by JavaScript, the HTML5 Canvas API enables web developers to create visualizations and animations right in the browser without Flash. Although the HTML5 Canvas is quickly becoming the standard for online graphics and interactivity, many developers fail to exercise all of the features that this powerful technology has to offer.The HTML5 Canvas Cookbook begins by covering the basics of the HTML5 Canvas API and then progresses by providing advanced techniques for handling features not directly supported by the API such as animation and canvas interactivity. It winds up by providing detailed templates for a few of the most common HTML5 canvas applications—data visualization, game development, and 3D modeling. It will acquaint you with interesting topics such as fractals, animation, physics, color models, and matrix mathematics. By the end of this book, you will have a solid understanding of the HTML5 Canvas API and a toolbox of techniques for creating any type of HTML5 Canvas application, limited only by the extent of your imagination.

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HTML5 Canvas Cookbook
Eric Rowell
Nov, 2011 | 348 pages
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Table of Contents (19 chapters)
HTML5 Canvas Cookbook
HTML5 Canvas Cookbook
Credits
Credits
About the Author
About the Author
About the Reviewers
About the Reviewers
www.PacktPub.com
www.PacktPub.com
Preface
Preface
Free Chapter
1
Getting Started withPaths and Text
Getting Started withPaths and Text
Introduction
Drawing a line
How it works...
There's more...
See also...
Drawing an arc
Drawing a Quadratic curve
Drawing a Bezier curve
Drawing a zigzag
Drawing a spiral
Working with text
Drawing 3D text with shadows
Unlocking the power of fractals: Drawing a haunted tree
2
Shape Drawing and Composites
Shape Drawing and Composites
Introduction
Drawing a rectangle
Drawing a circle
Working with custom shapes and fill styles
Fun with Bezier curves: drawing a cloud
Drawing transparent shapes
Working with the context state stack to save and restore styles
Working with composite operations
Creating patterns with loops: drawing a gear
Randomizing shape properties: drawing a field of flowers
Creating custom shape functions: playing card suits
Putting it all together: drawing a jet
3
Working with Images and Videos
Working with Images and Videos
Introduction
Drawing an image
Cropping an image
Copying and pasting sections of the canvas
Working with video
Getting image data
Introduction to pixel manipulation: inverting image colors
Inverting video colors
Converting image colors to grayscale
Converting a canvas drawing into a data URL
Saving a canvas drawing as an image
Loading the canvas with a data URL
Creating a pixelated image focus
4
Mastering Transformations
Mastering Transformations
Introduction
Translating the canvas context
Rotating the canvas context
Scaling the canvas context
Creating a mirror transform
Creating a custom transform
Shearing the canvas context
Handling multiple transforms with the state stack
Transforming a circle into an oval
Rotating an image
Drawing a simple logo and randomizing its position, rotation, and scale
5
Bringing the Canvas to Life with Animation
Bringing the Canvas to Life with Animation
Introduction
Creating an Animation class
Creating a linear motion
Creating acceleration
Creating oscillation
Oscillating a bubble
Swinging a pendulum
Animating mechanical gears
Animating a clock
Simulating particle physics
Creating microscopic life forms
Stressing the canvas and displaying the FPS
6
Interacting with the Canvas: Attaching Event Listeners to Shapes and Regions
Interacting with the Canvas: Attaching Event Listeners to Shapes and Regions
Introduction
Creating an Events class
Working with canvas mouse coordinates
Attaching mouse event listeners to regions
Attaching touch event listeners to regions on a mobile device
Attaching event listeners to images
Dragging-and-dropping shapes
Dragging-and-dropping images
Creating an image magnifier
Creating a drawing application
7
Creating Graphs and Charts
Creating Graphs and Charts
Introduction
Creating a pie chart
Creating a bar chart
Graphing equations
Plotting data points with a line chart
8
Saving the World with Game Development
Saving the World with Game Development
Introduction
Creating sprite sheets for the heroes and enemies
Creating level images and boundary maps
Creating an Actor class for the hero and enemies
Creating a Level class
Creating a Health Bar class
Creating a Controller class
Creating a Model class
Creating a View class
Setting up the HTML document and starting the game
9
Introducing WebGL
Introducing WebGL
Introduction
Creating a WebGL wrapper to simplify the WebGL API
Creating a triangular plane
Rotating a triangular plane in 3D space
Creating a rotating cube
Adding textures and lighting
Creating a 3D world that you can explore
Detecting Canvas Support
Detecting Canvas Support
Canvas fallback content
Canvas Security
Canvas Security
Additional Topics
Additional Topics
Canvas vs. CSS3 transitions and animations
Canvas performance on mobile devices
Index
Index

Creating a Health Bar class

In this recipe, we'll create a Health Bar class which is used to update and render the hero's health display.

How to do it...

Follow these steps to create a health bar class:

  1. Define the HealthBar constructor:

    /*
 * HealthBar class should have no knowledge
 * of the Actor or Level classes to
 * keep it decoupled
 */
function HealthBar(config){
  this.controller = config.controller;
    this.maxHealth = config.maxHealth;
    this.x = config.x;
    this.y = config.y;
    this.maxWidth = config.maxWidth;
    this.height = config.height;
    
    this.health = this.maxHealth;
}

  2. Define the setHealth() method which sets the health value:

    HealthBar.prototype.setHealth = function(health){
    this.health = health;
};

  3. Define the draw() method which draws the health bar:

    HealthBar.prototype.draw = function(){
  var context = this.controller.view.context;
    context.beginPath();
    context.rect(this.x, this.y, this.maxWidth, this.height);
    context.fillStyle = "black";
    context...
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