13: THUNDERING YOUR SITE WITH CANVAS in .NET framework

Making QR Code 2d barcode in .NET framework 13: THUNDERING YOUR SITE WITH CANVAS
CHAPTER 13: THUNDERING YOUR SITE WITH CANVAS
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contextNow.drawImage(pic,0,0); contextNow.fillStyle = rgba(242, 208, 145, .6) ; contextNow.fillRect(0,0,472,306); contextNow.fill();
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If the drawing is added first, the image simply sits on top of it as though no filter at all is used. Now, with the added filter, the image better fits in with the page, as Figure 13-9 shows.
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Figure 13-9: A ltered image blending in with the background.
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Using Adobe Photoshop or some similar image-editing software, you could ve added the filter to the image and loaded the filtered image with a standard <img> tag. However, using canvas and HTML5, you can make the changes without any additional software.
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CREATING COMPLEX DRAWINGS WITH CANVAS
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The simpler shapes are rectangles, and they re terrific for squares and rectangles, but you can only do so much with boxes before you need some lines and curves. This section looks at the following complex drawing elements that are part of canvas. (The context term refers to the name of the rendering context object.)
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context.beginPath() context.moveTo(x, y) context.closePath() context.lineTo(x, y) context.quadraticCurveTo(cpx, cpy, x, y) context.bezierCurveTo(cp1x, cp1y, cp2x, cp2y, x, y) context.arcTo(x1, y1, x2, y2, radius) context.arc(x, y, radius, startAngle, endAngle, anticlockwise) context.rect(x, y, w, h) context.fill() context.stroke() context.clip() context.isPointInPath(x, y)
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Knowing how to use these methods with a <canvas> tag doesn t ensure that they ll look good. The remainder of this chapter examines most of these methods. You should be well on your way to creating many different shapes by the chapter s end.
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LINES AND MOVEMENT
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270 The best way to start thinking about using the canvas tools for drawing is to visualize all drawings on a grid, just as you did with rectangles. However, given the relative complexity of freeform drawing, even with straight lines, the beginning point is with images on a grid. Figure 13-10 shows two drawings that can be created with straight lines.
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0,0 Each grid box is 20 x 20 pixels.
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Figure 13-10: Images on a grid.
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The grid boxes are 20 pixels wide and 20 pixels high. If you take a pencil and a piece of grid paper (or turn on the grid on a drawing program), you can replicate the images in Figure 13-10. Starting with the left image in Figure 13-10, a typical drawing would consist of the following steps:
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CHAPTER 13: THUNDERING YOUR SITE WITH CANVAS
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1. Place the pencil at position 40,20 on the grid. To do this with the canvas DOM, use context.beginPath() and context. moveTo(40,20). This is the starting point. 2. Draw a line from the starting point to about 72, 20 for the top of the briefcase handle. Use context.lineTo(72,20) for the canvas equivalent. 3. Move the pencil down to about 72, 38. Use context.lineTo(72,38) for a canvas drawing. 4. Continue in this manner until the outline of the briefcase is complete. 5. When you want to draw the inside of the handle, pick up your pencil, move to where you want to start drawing the inside of the handle. With canvas you use context.moveTo(x,y) to begin in a new position and then use context.lineTo(x,y) to finish up. However, you do not have to reuse context.beginPath(). 6. In a pencil and pen drawing, as soon as your drawing is complete, you have the outline of the briefcase. With canvas, you have to include context.stroke() to add the lines. When you come to the next-to-last point in your drawing, you can use the context. closePath() method to go the point you started, and that is used in the program. The following script (SimpleLineDrawing.html in this chapter s folder at www.wiley. com/go/smashinghtml5) provides all the steps.
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<!DOCTYPE html> <html> <head> <script language= javascript > //colors: 8C6E37,BFA380 CanvasMaster=new Object(); CanvasMaster.showCanvas=function() { canvasNow = document.getElementById( simpleDraw ); contextNow = canvasNow.getContext( 2d ); contextNow.beginPath(); contextNow.moveTo(40,20); contextNow.lineTo(72,20); contextNow.lineTo(72,38); contextNow.lineTo(88,38); contextNow.lineTo(88,78); contextNow.lineTo(28,78); contextNow.lineTo(28,38); contextNow.lineTo(40,38); contextNow.lineTo(40,20); contextNow.closePath(); contextNow.moveTo(46,26); contextNow.lineTo(66,26); contextNow.lineTo(66,38);
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contextNow.lineTo(46,38); contextNow.closePath(); contextNow.stroke(); } </script> <style type= text/css > body { font-family:Verdana; color:#000000; } </style> <title>Filtering Images</title> </head> <body onLoad= CanvasMaster.showCanvas() > <article> <figure> <canvas id= simpleDraw width= 90 height= 80 > If you can identify the drawing, you win a jillion dollars! Oh, I m sorry . . . looks like you don t have an HTML5 browser.</canvas> <figcaption> <br/> Picasso Was Here</figcaption> </figure> </article> </body> </html>
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Figure 13-11 shows what you can expect to see. (If you worked out the coordinates on your own, yours probably looks better!)