190 lines
8.6 KiB
HTML
190 lines
8.6 KiB
HTML
<!DOCTYPE html>
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<html>
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<head>
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<meta http-equiv="X-UA-Compatible" content="chrome=1">
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<!--
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/**
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* o------------------------------------------------------------------------------o
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* | This file is part of the OfficeExcel package - you can learn more at: |
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* | |
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* | http://www.OfficeExcel.net |
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* | |
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* | This package is licensed under the OfficeExcel license. For all kinds of business |
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* | purposes there is a small one-time licensing fee to pay and for non |
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* | commercial purposes it is free to use. You can read the full license here: |
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* | |
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* | http://www.OfficeExcel.net/LICENSE.txt |
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* o------------------------------------------------------------------------------o
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*/
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-->
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<title>A short description of what HTML5 canvas is</title>
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<meta name="keywords" content="OfficeExcel html5 canvas charts what " />
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<meta name="description" content="A short description of the HTML5 canvas tag" />
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<meta name="googlebot" content="NOODP">
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<meta property="og:title" content="OfficeExcel: What is HTML5 canvas?" />
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<meta property="og:description" content="A brief description and a few examples of HTML5 canvas " />
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<meta property="og:image" content="http://www.OfficeExcel.net/images/logo.png"/>
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<link rel="stylesheet" href="../css/website.css" type="text/css" media="screen" />
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<link rel="icon" type="image/png" href="../images/favicon.png">
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<!-- Place this tag in your head or just before your close body tag -->
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<script type="text/javascript" src="https://apis.google.com/js/plusone.js"></script>
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<script src="../libraries/OfficeExcel.common.core.js" ></script>
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<script src="../libraries/OfficeExcel.common.tooltips.js" ></script>
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<script src="../libraries/OfficeExcel.bar.js" ></script>
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<!--[if lt IE 9]><script src="../excanvas/excanvas.original.js"></script><![endif]-->
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<?php PrintAnalyticsCode() ?>
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</head>
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<body>
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<!-- Social networking buttons -->
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<?php
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$prefix = substr($_SERVER['SERVER_NAME'], 0, 3);
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require("/OfficeExcel.{$prefix}/social.html");
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?>
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<!-- Social networking buttons -->
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<div id="breadcrumb">
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<a href="../index.html">OfficeExcel: HTML5 Javascript charts library</a>
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>
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<a href="./index.html">Documentation</a>
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>
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What is HTML5 canvas?
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</div>
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<h1>What <span>is HTML5 canvas?</span></h1>
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<script>
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if (OfficeExcel.isOld()) {
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document.write('<div style="background-color: #fee; border: 2px dashed red; padding: 5px"><b>Important</b><br /><br /> Internet Explorer does not natively support the HTML5 canvas tag, so if you want to see the charts, you can either:<ul><li>Install <a href="http://code.google.com/chrome/chromeframe/">Google Chrome Frame</a></li><li>Use ExCanvas. This is provided in the OfficeExcel Archive.</li><li>Use another browser entirely. Your choices are Firefox 3.5+, Chrome 2+, Safari 4+ or Opera 10.5+. </li></ul> <b>Note:</b> Internet Explorer 9 fully supports the canvas tag.</div>');
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}
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</script>
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<ul>
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<li><a href="#introduction">Introduction</a></li>
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<li><a href="#history">History</a></li>
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<li><a href="#example">Example</a></li>
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<li><a href="#compare">Canvas compared to SVG</a></li>
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<li><a href="#support">Browser support for HTML5 canvas</a></li>
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</ul>
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<a name="introduction"></a>
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<h2>Introduction</h2>
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<p>
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HTML5 canvas is a new HTML tag (<i><canvas></i>) which is part of the forthcoming HTML5 standard. It allows bitmap
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drawing which is controlled using Javascript, and is what the OfficeExcel libraries use to draw the charts. You could
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liken it to a piece of paper which is part of your HTML page, on to which you can draw. Because you use Javascript to
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draw on the canvas it becomes part of your page and allows interaction very easily.
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</p>
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<p>
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Canvas uses a "fire and forget" drawing methodology - there is no DOM that is maintained, so if you want to alter something
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you will probably have to redraw the entire canvas. The lack of a DOM means that canvas is fast to draw on and very
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responsive - important when you're providing iteractive charts to your users.
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</p>
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<a name="history"></a>
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<h2>History</h2>
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<p>
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HTML5 canvas was originally introduced by Apple for use in WebKit (which is used in their Safari browser and Google Chrome).
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It is now part of the HTML5 specification and supported by all modern web browsers.
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</p>
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<a name="example"></a>
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<h2>Example</h2>
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<canvas id="cvs" width="350" height="250" style="border: 1px dashed gray; float: right">[No canvas support]</canvas>
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<script>
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window.onload = function ()
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{
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canvas = document.getElementById("cvs");
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context = canvas.getContext('2d');
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// Draw the red triangle
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context.beginPath();
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context.strokeStyle = 'black';
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context.fillStyle = 'red';
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context.moveTo(100, 25);
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context.lineTo(150, 100);
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context.lineTo(50, 100);
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context.lineTo(100, 25);
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context.stroke();
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context.fill();
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// Draw the blue square
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context.beginPath();
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context.fillStyle = 'rgba(0,0,255,0.5)';
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context.strokeRect(100, 75, 100,100);
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context.fillRect(100, 75, 100,100);
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context.stroke();
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context.fill();
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// Draw the yellow circle
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context.beginPath();
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context.globalAlpha = 0.5;
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context.fillStyle = 'yellow';
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context.arc(200,175,50,0,2 * Math.PI, 0);
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context.stroke();
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context.fill();
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}
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</script>
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<p>
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The example to the right is a very simple case of drawing a few primitives on the canvas. The dotted border is
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provided by CSS to illustrate the drawing area.
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</p>
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<p>
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The <canvas> tag itself is defined with just a width/height/id attribute. The one here also has a style attribute
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to make it more evident in the page. The HTML used is shown below:
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</p>
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<br clear="all" />
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<pre class="code">
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<canvas id="cvs" width="375" height="250">[No canvas support]<canvas>
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</pre>
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The content in between the tags is not shown if the browser supports canvas, and is if the browser doesn't. This provides
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for fallback content if the users browser doesn't support canvas.
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<a name="compare"></a>
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<h2>HTML5 Canvas compared to SVG</h2>
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<p>
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HTML5 canvas can be compared (a bit) to SVG - which is a vector based alternative for drawing in HTML pages. SVG is
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at a more abstract level than canvas and maintains a record of everything drawn, using a DOM. This is then converted
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to a bitmap when shown. In the above example, if the blue squares coordinates are changed (eg in an animation),
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then the whole canvas needs to be cleared and redrawn for each frame of that animation.
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</p>
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<p>
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As a result of not having to maintain a DOM though, <canvas> is fast to draw on and display to the browser.
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</p>
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<a name="support"></a>
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<h2>Browser support for HTML5 canvas</h2>
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<p>
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Modern browsers supporting HTML5 support canvas, including IE9+. Earlier versions of MSIE have some support through
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compatibility layers provided by Google and Mozilla. One such library - ExCanvas - is provided in the OfficeExcel archive
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allowing IE7 and 8 to display the graphs, albeit without many of the dynamic features. You can read more on this
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<a href="msie.html">here</a>.
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</p>
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<p align="right">
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<b>
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<a href="index.html">Full documentation »</a>
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</b>
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</p>
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</body>
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</html> |