source: src/olheatmap/js/Heatmap.php

/*  OpenLayersHeatmap
 *  Copyright (C) 2010 Felipe Barriga Richards
 *
 *  This Program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2, or (at your option)
 *  any later version.
 *
 *  This Program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with RTMPDump; see the file COPYING.  If not, write to
 *  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 *  Boston, MA  02110-1301, USA.
 *  http://www.gnu.org/copyleft/gpl.html
 *
 */
 
/*
 * Edited by Dennis Wagenaar
 */


<?php
function connectdb()
{
 mysql_connect("location", "username", "password")
  or die("Error connecting to mysql: " . mysql_error());
 mysql_select_db('database')
  or die("Error connecting to database: " . mysql_error());
}
connectdb();
$table = 'table';
?>


var layerMapnik = null;
var lastZoom = null;
var vectorStyleCache = null;

function addToVectorStyleCache(vectorStyle, hash) {
        if (vectorStyleCache == null)
                vectorStyleCache = new Array();
        vectorStyleCache[hash] = vectorStyle;
}


function getVectorStyle(size, color) {
        var vectorStyle = null;
        var hash = size + '_' + color;
        if ( (vectorStyleCache != null) && (vectorStyleCache[hash] != null) ) {
                vectorStyle = vectorStyleCache[hash];
        } else {
                vectorStyle = OpenLayers.Util.extend({}, OpenLayers.Feature.Vector.style['default']);
                vectorStyle.graphicWidth  = size;
                vectorStyle.graphicHeight = size;
                vectorStyle.graphicXOffset = -size/2;
                vectorStyle.graphicYOffset = -size/2;
                vectorStyle.externalGraphic = 'images/marker_' + color + '.png';

                addToVectorStyleCache(vectorStyle, hash);
        }
        return vectorStyle;
}


function scaleRadius(radius) {
  var zoom = map.getZoom();
  var scaleFactor = 1 / (1.1 * Math.pow(2, 16 - zoom));
  radius *= scaleFactor;

  return radius;
}


function drawMarkers() {

        var points = new Array();
        var lonLat, vectorStyle, point, pointVector, color, size;
        
        layerVectors.destroyFeatures();

                <?php
                $result=mysql_query("SELECT longitude, latitude FROM ".$table." ");
                while($row=mysql_fetch_array($result))
                { 
                echo "lonLat = new OpenLayers.LonLat(".$row['longitude'].", ".$row['latitude'].").transform(map.displayProjection,map.getProjectionObject());";
                echo "color = 'green';
                size = '25';
                size = scaleRadius(size);
                vectorStyle = getVectorStyle(size, color);
                point = new OpenLayers.Geometry.Point(lonLat.lon, lonLat.lat);
                pointVector= new OpenLayers.Feature.Vector(point, null, vectorStyle);
                points.push(pointVector);";
                }
                ?>
        

        layerVectors.addFeatures(points);
}


function generateHeatmap() {
        var width               = layerVectors.renderer.canvas.canvas.width;
        var height              = layerVectors.renderer.canvas.canvas.height;

        var context             = layerVectors.renderer.canvas.canvas.getContext('2d');
        var myImageData = context.getImageData(0, 0, width, height);
        var pix                 = myImageData.data;

        for (var i = 0, n = pix.length; i < n; i += 4) {
                // i+3 is alpha (the fourth element)
                if (pix[i+3] <= 64) {
                        pix[i+2] = 255;                 // blue
                        pix[i+1] = (255/64)*pix[i+3];   // green
                        pix[i  ] = 0;                   // red
                } else if (pix[i+3] <= 128) {
                        pix[i+1] = 255;
                        pix[i+2] = (255/64)*(128-pix[i+3]);
                        pix[i  ] = 0;
                } else if (pix[i+3] <= 192) {
                        pix[i+1] = 255;
                        pix[i+2] = 0;
                        pix[i  ] = (255/64)*(pix[i+3]-128);
                } else if (pix[i+3] <= 255) {
                        pix[i+1] = (255/64)*(255-pix[i+3]);
                        pix[i+2] = 0;
                        pix[i  ] = 255;
                }
        }
        context.putImageData(myImageData, 0, 0);
}


function mapMoveEndEvent(event) {
        if (event.type == 'moveend') {
                if (lastZoom != map.getZoom()) {
                        lastZoom = map.getZoom();
                        onChangeParams(true);
                }
                Concurrent.Thread.create(function() {
                        Concurrent.Thread.sleep(50);
                        layerVectors.renderer.redraw();
                })
        }
}


function onChangeParams(_drawMarkers) {
        vectorStyleCache = null;
        if (_drawMarkers)
                drawMarkers();
}

function clearMarkers() {
        markers = new Array();
        vectorialMarkers = new Array();
        layerVectors.destroyFeatures();
}



function init() {  
        map = new OpenLayers.Map("heatmap", {
                eventListeners: {
                        "moveend": mapMoveEndEvent
                },
                controls: [
                        new OpenLayers.Control.Navigation(),
                        new OpenLayers.Control.PanZoomBar(),
                        new OpenLayers.Control.ScaleLine()
                ],
                maxExtent: new OpenLayers.Bounds(-20037508.34,-20037508.34,20037508.34,20037508.34),
                maxResolution: 156543.0399,
                numZoomLevels: 19,
                units: 'm',
                projection: new OpenLayers.Projection("EPSG:900913"),
                displayProjection: new OpenLayers.Projection("EPSG:4326")
        });

        layerMapnik = new OpenLayers.Layer.OSM.Mapnik("Mapnik");
        map.addLayer(layerMapnik);
        
        layerVectors = new OpenLayers.Layer.Vector("Features", {renderers: ["Canvas"]});
        map.addLayer(layerVectors);

        var lon   = 4.4585017;
        var lat   = 52.1406583;
        var zoom  = 16;

        var lonLat = new OpenLayers.LonLat(lon, lat).transform(new OpenLayers.Projection("EPSG:4326"), map.getProjectionObject());
        map.setCenter (lonLat, zoom);

        lastZoom = zoom;

}