Output renderers

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Output renderers
Project state	Specification
Tracker issue	MDL-21235
Discussion	n/a
Assignee	Petr Škoda (škoďák) + David Mudrak + feedback and ideas from other developers

Moodle 2.0

Goals

• stable API
• easy to use
• easy to customise via themes

Renderers

Output renderer is a class with collection of methods that handle rendering of visual aspects of Moodle pages, emails, html export, etc. In 1.9 general output related functions were located in weblib.php and modules stored rendering code in lib.php, locallib.php, view.php, etc.

Output renderer instances are obtained through moodle_page::get_renderer($component, $subtype = null, $target = null) method. Current core_renderer is available through the global $OUTPUT variable, please note this global should not be used in low level APIs.

Renderer targets

I most cases we are rendering page output for web browsers, sometimes we need to generate different output for command line scripts, email messages, etc.

renderer_base

Abstract class every other renderer must extend. Renderer base implements basic methods and support for renderer dispatching. The most important method is render(), it is using class name of the widget passed in first parameter to find fine correct protected rendering method (widget rendering methods have render_ prefix.

core_renderer

Core renderer implements:

1. page header and footer related rendering
2. boxes and containers
3. general widget methods - heading, single button, select form, heading, arrows, language selection, user login info
4. error messages, notifications
5. blocks

For example user avatar rendering involves following methods and classes: class core_renderer extends renderer_base {

 // ...

 public function render(widget $widget) {
    // calls $this->render_user_image($widget) when parameter with class user_image submitted 
 }
 protected function render_user_picture(user_picture $userpicture) {
   // returns html markup for user avatar
 }
 public function user_picture($userrecord, array $options=null) {
   // helper method that constructs $user_image widget and calls $this->render
   $picture = new user_picture($userrecord, $options);
   return $this->render($picture);
 }

 // ...

}

class user_picture extends widget {

 public $userrecord;
 public $options;

 public function __construct($userrecord, array $options=null) {
     // ...
 }

}

Developer has two options, either call

echo $OUTPUT->user_picture($user);

or create new instance:

$picture = new user_picture($user);
echo $OUTPUT->render($picture);

The point is that the first is usually one line only, it is also possible to have multiple helpers with different parameters. The second options enables more options without cluttering the simple API with tens of optional method parameters.

core_renderer_cli

_cli suffix indicates this is a core renderer for CLI rendering target (CLI scripts). For example headings are using => instead if H2 html tag.

Bootstrap renderer

Bootstrap renderer is used as a temporary $OUTPUT before the full initialisation of standard core renderer.

See also

• Theme_changes