Peter Lubbers - Pro HTML 5 Programming

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Download from Wow! eBook 42 CHAPTER 2 ■ USING THE HTML5 CANVAS API Drawing Curves The world, particularly the natural world, is not filled with straight lines and rectangles. Fortunately, the canvas provides a variety of functions for creating curves in our paths. We will demonstrate the simplest option—a quadratic curve—to form a path through our virtual forest. Listing 2-13 demonstrates the addition of two quadratic curves. Listing 2-13. Drawing a curve // Save the canvas state and draw the path context.save(); context.translate(-10, 350); context.beginPath(); // The first curve bends up and right context.moveTo(0, 0); context.quadraticCurveTo(170, -50, 260, -190); // The second curve continues down and right context.quadraticCurveTo(310, -250, 410,-250); // Draw the path in a wide brown stroke context.strokeStyle = '#663300'; context.lineWidth = 20; context.stroke(); // Restore the previous canvas state context.restore(); As before, one of the first things we will do is save our canvas context state, because we will be modifying the translation and stroke options here. For our forest path, we will start by moving back to the origin and drawing a first quadratic curve up and to the right. As shown in Figure 2-10, the quadraticCurveTo function begins at the current drawing location and takes two x, y point locations as its parameters. The second one is the final stop in our curve. The first one represents a control point. The control point sits to the side of the curve (not on it) and acts almost as a gravitational pull for the points along the curve path. By adjusting the location of the control point, you can adjust the curvature of the path you are drawing. We draw a second quadratic curve up and to the right to complete our path; then stroke it just as we did for our tree canopy before (only wider).
Figure 2-10. Quadratic curve start, end, and control points CHAPTER 2 ■ USING THE HTML5 CANVAS API Other options for curves in the HTML5 Canvas API include the bezierCurveTo, arcTo, and arc functions. These curves take additional control points, a radius, or angles to determine the characteristics of the curve. Figure 2-11 shows the two quadratic curves stroked on our canvas to create a path through the trees. Figure 2-11. Quadratic curves for a path 43
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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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Page 17 and 18: About the Technical Reviewer � Pa
Page 19 and 20: Introduction HTML5 is brand new. In
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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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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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Basic API Usage CHAPTER 6 ■ USING
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HTML5 WebSocket / Geolocation Track
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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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284 ■ INDEX stopping Web Workers,
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Peter Lubbers - Pro HTML 5 Programming

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