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Output Filters

Output Filters allow you to modify the output, after all variables have been added and the template has been parsed. You could use it, to remove unecessesary whitespace, compress the output or obfuscate all email addresses.

Creating you own output filter

An output filter has to be a class that extends from patTemplate_OutputFilter. You have to place the file that conatains your filter in the folder patTemplate/OutputFilter. In this class you only need to implement one method called apply(). This method will be called by patTemplate when patTemplate::displayParsedTemplate() is called by the script. Before the resulting HTML code is sent to the browser, your filter will have the oportunity to modify or filter the resulting HTML. The apply method has to accept one string parameter, in which it will receive the HTML code. After modifying it, you just have to return to modified HTML.

A simple example

The following example shows how to implement an output filter, that removes all linebreaks and extra spaces, indentations, etc. from the HTML code before sending it to the browser. The class has to be placed in the file patTemplate/OutputFilter/StripWhitespace.php (actually it already is there as this example is included in the distribution).

<?PHP
/**
 * patTemplate StripWhitespace output filter
 *
 * Will remove all whitespace and replace it with a single space.
 *
 * @package       patTemplate
 * @subpackage    Filters
 * @author        Stephan Schmidt <schst@php.net>
 */
class patTemplate_OutputFilter_StripWhitespace extends patTemplate_OutputFilter
{
   /**
    * filter name
    *
    * @access    protected
    * @abstract
    * @var    string
    */
    var    $_name    =    'StripWhitespace';

   /**
    * remove all whitespace from the output
    *
    * @access    public
    * @param    string        data
    * @return    string        data without whitespace
    */
    function apply( $data )
    {
        $data = str_replace( "\n", ' ', $data );
        $data = preg_replace( '/\s\s+/', ' ', $data );
    
        return $data;
    }
}
?>

Applying output filters

Applying an output filter is an easy task. You just have to call one method on your patTemplate object and pass the desired output filter. You may create a filter chain by applying as many output filters as you like. If you applied more than one filter, the will be called in the same order as you applied them.

<?PHP
require_once 'pat/patErrorManager.php';
require_once 'pat/patTemplate.php';

$tmpl = &new patTemplate();
$tmpl->setRoot( 'templates' );
$tmpl->applyOutputFilter( 'StripWhitespace' );

$tmpl->readTemplatesFromInput( 'page.tmpl', 'File' );

/**
 * output filter will be applied here
 */
$tmpl->displayParsedTemplate();
?>

Passing parameters to the filter

You may also create an output filter that can be parameterised by the script that applies the filter. If the filter class needs to access the parameters set by the script, you may use the method patTemplate_OutputFilter::getParam(). When applying a filter, all parameters have to be passed as an array in the second parameter of patTemplate::applyOutputFilter().