Difference between revisions of "Real-time graphing"

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Line 34: Line 34:
 
                     ydat.splice(0,1);
 
                     ydat.splice(0,1);
 
                 }
 
                 }
                 y.push(a);
+
                 ydat.push(a);
 
                 if (!g) {                  // If the curve does not exist yet, create it.
 
                 if (!g) {                  // If the curve does not exist yet, create it.
 
                     g = brd.createElement('curve', [xdat,ydat],{strokeWidth:3, strokeColor:'yellow'});  
 
                     g = brd.createElement('curve', [xdat,ydat],{strokeWidth:3, strokeColor:'yellow'});  

Revision as of 09:40, 18 December 2009

The underlying JavaScript code

  <script type="text/javascript" src="http://jsxgraph.uni-bayreuth.de/distrib/prototype.js"></script>
  <style>
    #jxgbox {
       background-color:black;
    }
  </style>
var brd, g, 
    x = [], y = [];

brd = JXG.JSXGraph.initBoard('jxgbox', {axis:true, boundingbox:[0,20,30,-2]});

fetchData = function() {
    new Ajax.Request('/ajax/fakesensor.php', {
        onComplete: function(transport) {
            var t, a;
            if (200 == transport.status) {
                t = transport.responseText;
                a = parseFloat(t);
                if (x.length<30) {
                    x.push(x.length);
                } else {
                    y.splice(0,1);
                }
                y.push(a);
                if (!g) {                   // If the curve does not exist yet, create it.
                    g = brd.createElement('curve', [x,y],{strokeWidth:3, strokeColor:'green'}); 
                } 
                brd.update();
            };
    }});
};

Start = function() {
    periodical = setInterval(fetchData,1000);  // Start the periodical update
};

Start();

The PHP code of fakesensor.php

<?php
   echo mt_rand(0,20);
?>