heatmap write access

README.md

@@ -206,9 +206,10 @@ sudo a2enmod rewrite
 sudo systemctl restart apache2
 ```
 
-For the symbols cache to work we need to make sure the webserver has write access to our htdocs/public/symbols directory (the following permission may be a little bit too generous...)
+For the symbols and heatmap caches to work we need to make sure the webserver has write access (the following permission may be a little bit too generous...)
 ```
 chmod 777 ~/trackdirect/htdocs/public/symbols
+chmod 777 ~/trackdirect/htdocs/public/heatmaps
 ```
 
 If you have enabled a firewall, make sure port 80 is open.

htdocs/public/heatmaps/heatmap.php

@@ -77,7 +77,10 @@ $config = array(
 );
 
 $heatmap = new gd_heatmap($data, $config);
-//$heatmap->output();
 
-$heatmap->output($filename);
-readfile($filename);
+if (is_writable(dirname($filename))) {
+    $heatmap->output($filename);
+    readfile($filename);
+} else {
+    $heatmap->output();
+}