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21 <title>RGraph: HTML5 canvas graph library - Asynchronous processing</title>
23 <meta name="keywords" content="rgraph html5 canvas graph docs async asynchronous" />
24 <meta name="description" content="RGraph: HTML5 canvas graph software - Documentation about asynchronous processing" />
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30 <script src="../libraries/RGraph.line.js"></script>
31 <!--[if IE 8]><script src="../excanvas/excanvas.compressed.js"></script><![endif]-->
34 window.onload = function ()
36 var duration = (new Date().getTime() - timer.getTime()) / 1000;
37 document.getElementById("waiting").innerHTML = '<span style="color: green">Done! Extra time taken: ' + duration.toFixed(1) + ' seconds</span>';
38 alert('The window.onload event fired, extra time taken: ' + duration.toFixed(1) + ' seconds');
41 // Create a timer to show the difference
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51 function HideTwitterDIV ()
53 document.getElementById("twitter_div").style.opacity = 0;
54 document.getElementById("twitter_div").style.display = 'none';
58 function ShowTwitterDIV (e)
60 var e = RGraph.FixEventObject(document.all ? event : e);
61 var div = document.getElementById("twitter_div");
62 var img = document.getElementById("twitter_icon");
64 div.style.display = 'block';
65 div.style.left = (RGraph.getCanvasXY(img)[0] + img.offsetWidth - div.offsetWidth + 110) + 'px';
66 div.style.top = (RGraph.getCanvasXY(img)[1] - 1) + 'px';
71 setTimeout('document.getElementById("twitter_div").style.opacity = 0.2;', 25);
72 setTimeout('document.getElementById("twitter_div").style.opacity = 0.4;', 50);
73 setTimeout('document.getElementById("twitter_div").style.opacity = 0.6;', 100);
74 setTimeout('document.getElementById("twitter_div").style.opacity = 0.8;', 125);
75 setTimeout('document.getElementById("twitter_div").style.opacity = 1.0;', 150);
83 * This code installs the event handler that hides the Twitter DIV
86 window.attachEvent('onload', function () {document.body.attachEvent('onclick', HideTwitterDIV);});
88 window.addEventListener('click', HideTwitterDIV, false);
92 <!-- The twitter DIV -->
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143 <div id="breadcrumb">
144 <a href="../index.html">RGraph: HTML5 canvas graph library</a>
146 <a href="index.html">Documentation</a>
148 Asynchronous processing
151 <h1>RGraph: HTML5 canvas graph library - Asynchronous processing</h1>
154 if (RGraph.isIE8()) {
155 document.write('<div style="background-color: #fee; border: 2px dashed red; padding: 5px"><b>Important</b><br /><br /> Internet Explorer 8 does not natively support the HTML5 canvas tag, so if you want to see the graphs, 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 RGraph 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. Click <a href="http://groups.google.com/group/rgraph/browse_thread/thread/c5651ff8c56b8f3c#" target="_blank">here</a> to see some screenshots.</div>');
159 <p id="waiting" style="; font-weight: bold; font-size: 16pt"><span style="color: #aa0">Waiting for onload event...</span></p>
161 <p style="background-color: #eee; border: 1px dashed gray; padding: 5px; height: 50px;">
162 <span style="display: inline-block; margin-left: 10px; float: right">
164 document.write('<img src="http://ie.microsoft.com/testdrive/HTML5/DOMContentLoaded/whidbey.jpg?' + Math.random() + '" width="50" height="50" /> ');
165 document.write('<img src="http://ie.microsoft.com/testdrive/HTML5/DOMContentLoaded/window.jpg?' + Math.random() + '" width="50" height="50" /> ');
166 document.write('<img src="http://ie.microsoft.com/testdrive/HTML5/DOMContentLoaded/whidbey2.jpg?' + Math.random() + '" width="50" height="50" />');
170 These images are here to pad the page and slow down loading so that the window.onload event is slowed. This makes the
171 difference far more visible.
174 <canvas id="myCanvas" width="600" height="250" style="float: right">[No canvas support]</canvas>
178 * Create the line graph
180 function CreateLineGraph ()
182 var line = new RGraph.Line('myCanvas', [1,2,4,2,1,3,5,6,6,5,3,5]);
183 line.Set('chart.title', 'Sales for Acme Inc.');
184 line.Set('chart.labels', ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']);
185 line.Set('chart.hmargin', 10);
186 line.Set('chart.linewidth', 5);
187 line.Set('chart.shadow', true);
188 line.Set('chart.shadow.offsetx', 0);
189 line.Set('chart.shadow.offsety', 0);
190 line.Set('chart.shadow.blur', 15);
194 RGraph.Async(CreateLineGraph);
198 Asynchronous processing can speed up the display of your graphs, because the browser gets to your code, sets it
199 going and then continues on rendering the page. Particularly if you have a weighty page,
200 it can make quite a difference. The <i>RGraph.Async()</i> function itself is very simple, but because it can make
201 a significant difference to the speed of your page, it is documented here. There's an example of it to the right.
202 One thing to remember is to ensure your canvas tag is defined first before you set the function that creates
207 Although asynchronous processing can speed up your pages, it can also give the appearance of slower pages due to partial
208 rendering, (ie your pages render a bit at a time). You therefore will need to experiment to get the best result for you.
214 <script src="RGraph.common.js"></script>
215 <script src="RGraph.line.js"></script>
217 <canvas id="myCanvas" width="300" height="100">[No canvas support]</canvas>
221 * Create the line graph
223 function CreateLineGraph ()
225 var line = new RGraph.Line('myCanvas', [1,2,4,2,1,3,5,6,6,5,3,5]);
226 line.Set('chart.title', 'Sales for Acme Inc.');
227 line.Set('chart.labels', ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']);
228 line.Set('chart.hmargin', 10);
229 line.Set('chart.linewidth', 5);
230 line.Set('chart.shadow', true);
231 line.Set('chart.shadow.offsetx', 0);
232 line.Set('chart.shadow.offsety', 0);
233 line.Set('chart.shadow.blur', 15);
237 RGraph.Async(CreateLineGraph);
241 <p><b>Things to remember</b></p>
244 <li>All your libraries must be loaded first. In the pages <head> for example. If not, you won't be able to create your graphs.</li>
245 <li>Your <canvas> tag must be defined before setting the asynchronous code going. If not, then the canvas may be referenced before it exists, and thus your graphs will not be created.</li>
247 The users connection speed may be a factor. Slower connections may mean, for example, that the onload event doesn't fire very
248 quickly. If you're using the onload event to create your graphs then asynchronous creation instead may give you more
249 apparent speed ups. Alternatively, careful placement of the <canvas> tag and the code that creates the graph may suffice
252 <li>Since the MSIE/ExCanvas combo requires you to use the window.onload event, aynchronous graph creation in this case will probably not be any help.</li>
254 Since a dev release of version 4, Google Chrome has had an issue when aynchronous processing is used, meaning that
255 text isn't always displayed. The solution here is simply to not use asynchronous processing. As of 27th March 2010,
256 Chrome 5 appears to be fine.
262 You might also be interested in the alternative, <a href="domcontentloaded.html">DOMContentLoaded</a> event.