Peter Lubbers - Pro HTML 5 Programming

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200 CHAPTER 8 ■ USING THE HTML5 WEB WORKERS API } } } document.getElementById("helloButton").onclick = function() { worker.postMessage("Here's a message for you"); document.getElementById("stopButton").onclick = stopWorker; window.addEventListener("load", loadDemo, true); Listing 8-3. Simple HTML5 Web Worker JavaScript file function messageHandler(e) { postMessage("worker says: " + e.data + " too"); } addEventListener("message", messageHandler, true); Building an Application with HTML5 Web Workers So far, we’ve focused on using the different Web Worker APIs. Let’s see how powerful the Web Workers API can really be by building an application: a web page with an image-blurring filter, parallelized to run on multiple Web Workers. Figure 8-4 shows what this application looks like in action.
Figure 8-4. HTML5 Web Worker–based web page with image-blurring filter CHAPTER 8 ■ USING THE HTML5 WEB WORKERS API This application sends image data from a canvas to several Web Workers (you can specify how many). The Web Workers then process the image with a simple box-blur filter. This may take several seconds, depending on the size of the image and the computational resources available (even machines with fast CPUs may have load from other processes, causing JavaScript execution to take more wallclock time to complete). However, because the heavy lifting takes place in Web Workers, there is no danger of slow-script warnings and, therefore, no need to manually partition the task into scheduled slices—something you would have to consider if you could not use Web Workers. Coding the blur.js Helper Script Inside the blur.js application page, we can use a straightforward implementation of a blur filter that loops until it has completely processed its input, as shown in Listing 8-4. 201
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THE EXPERT’S VOICE ® IN WEB DEVE
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■ ■ ■ Pro HTML5 Programming P
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For my beautiful wife, Vittoria, an
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Contents ■Foreword ..............
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■ CONTENTS Implementing Canvas Se
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■ CONTENTS Summary ..............
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■ CONTENTS Setting and Retrieving
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Foreword In June 2004, representati
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About the Technical Reviewer � Pa
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Introduction HTML5 is brand new. In
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C H A P T E R 1 ■ ■ ■ Overvie
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CHAPTER 1 ■ OVERVIEW OF HTML5 wit
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Interoperability Simplification CHA
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• MathML • Microdata • Server
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Figure 1-1. A page rendered in stan
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Table 1-2. New sectioning HTML5 ele
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CHAPTER 1 ■ OVERVIEW OF HTML5 Wit
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article { background-color: #eee; d
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Figure 1-2. An HTML5 page with all
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CHAPTER 1 ■ OVERVIEW OF HTML5 The
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Figure 1-3. Developer Tools view in
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CHAPTER 1 ■ OVERVIEW OF HTML5 All
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26 CHAPTER 2 ■ USING THE HTML5 CA
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C H A P T E R 3 ■ ■ ■ Working
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Audio and Video Codecs CHAPTER 3
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Table 3-1. Browser support for HTML
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MEDIA FOR EVERYONE CHAPTER 3 ■ WO
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CHAPTER 3 ■ WORKING WITH HTML5 AU
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Table 3-4 shows a few of the read-o
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find the actual frame since the vid
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LOSING VIEWERS IN THE OF AN EYE CH
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C H A P T E R 4 ■ ■ ■ Using t
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A device can use any of the followi
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Table 4-4. Pros and cons of cell ph
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Figure 4-1. HTML5 Geolocation brows
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CHAPTER 4 ■ USING THE HTML5 GEOLO
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Listing 4-6. The Haversine formula
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Listing 4-9. Adding the loadDemo()
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THE EASIEST WAY TO TRAVEL CHAPTER 4
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var deltaLatitude = toRadians(latit
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Practical Extras CHAPTER 4 ■ USIN
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Show Me on a Google Map CHAPTER 4
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CHAPTER 5 ■ USING THE COMMUNICATI
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var defaultTitle = "Portal [http://
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Send Notification CHAPTER 5 ■ U
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Figure 5-4. Difference between clie
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“SEEMINGLY ARBITRARY” TIMES CHA
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crossOriginRequest.upload.onprogres
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Figure 6-1. The complexity of real-
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Listing 6-2. The WebSocket interfac
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Listing 6-4. HTTP response header H
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Figure 6-4. Latency comparison betw
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EXISTING WEBSOCKET SERVERS CHAPTER
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250 CHAPTER 10 ■ CREATING HTML5 O
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C H A P T E R 11 ■ ■ ■ The Fu
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Figure 11-1. Quake II 3D Shaders CH
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CHAPTER 11 ■ THE FUTURE OF HTML5
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270 ■ INDEX unsupported, 68 using
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274 ■ INDEX Web SQL database supp
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276 ■ INDEX HTML5 page CSS file f
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278 ■ INDEX media elements. See a
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280 ■ INDEX building application
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284 ■ INDEX stopping Web Workers,
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Peter Lubbers - Pro HTML 5 Programming

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