Peter Lubbers - Pro HTML 5 Programming

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50 CHAPTER 2 ■ USING THE <strong>HTML</strong>5 CANVAS API context.lineWidth = 4; context.lineJoin = 'round'; context.strokeStyle = '#663300'; context.stroke(); context.fillStyle = '#339900'; context.fill(); } As you can see, the drawTree function contains all the code we previously created to draw the canopy, trunk, and trunk gradient. Now we will use one of the transformation routines— context.scale—to draw a second tree at a new location and with a larger size, as shown in Listing 2-20. Listing 2-20. Drawing the tree objects // Draw the first tree at X=130, Y=250 context.save(); context.translate(130, 250); drawTree(context); context.restore(); // Draw the second tree at X=260, Y=500 context.save(); context.translate(260, 500); // Scale this tree twice normal in both dimensions context.scale(2, 2); drawTree(context); context.restore(); The scale function takes two factors for the x and y dimensions as its arguments. Each factor tells the canvas implementation how much larger (or smaller) to make the size in that dimension; an X factor of 2 would make all subsequent draw routines twice as wide, while a Y factor of 0.5 would make all subsequent operations half as tall as before. Using these routines, we now have an easy way to create a second tree in our trails canvas, as shown in Figure 2-15.
Figure 2-15. Tree with a larger scale CHAPTER 2 ■ USING THE <strong>HTML</strong>5 CANVAS API ALWAYS PERFORM SHAPE AND PATH ROUTINES AT THE ORIGIN Brian says (and really means it, this time): “This example illustrates one of the reasons why it is a good idea to perform shape and path routines at the origin; then translate them when complete, as we do here in our code. The reason is that transforms such as scale and rotate operate from the origin. If you perform a rotate transform to a shape drawn off origin, a rotate transform will rotate the shape around the origin rather than rotating in place. Similarly, if you performed a scale operation to shapes before translating them to their proper position, all locations for path coordinates would also be multiplied by the scaling factor. Depending on the scale factor applied, this new location could even be off the canvas altogether, leaving you wondering why your scale operation just ‘deleted’ the image.” 51
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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
Page 19 and 20: Introduction HTML5 is brand new. In
Page 21 and 22: C H A P T E R 1 ■ ■ ■ Overvie
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Page 25 and 26: Interoperability Simplification CHA
Page 27 and 28: • MathML • Microdata • Server
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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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C H A P T E R 5 ■ ■ ■ Using t
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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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C H A P T E R 6 ■ ■ ■ Using t
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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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CHAPTER 6 ■ USING THE HTML5 WEBSO
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def terminate(self): self.ready_sta
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self.sessions = [] self.port = port
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Basic API Usage CHAPTER 6 ■ USING
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HTML5 WebSocket / Geolocation Track
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} } Summary incomingRow = docume
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170 CHAPTER 7 ■ USING THE HTML5 F
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244 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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