Development:Theme changes in 2.0

Note: This page is a work-in-progress. Feedback and suggested improvements are welcome. Please join the discussion on moodle.org or use the page comments.

Goals

The main goals are:

1. easier theme customisations - both CSS and images
2. simplify core and themes code
3. significant performance improvements
4. solve majority of browser caching problems
5. use YUI CSS foundation
6. allow themes to be stored in separate directory without www access (such as dataroot)

It should be easy to upgrade simple older themes. I think it is better if old themes are completely disabled with reasonable fallback mechanism. Why should we display broken themes during upgrade? Imagine users or teachers can select "broken" themes in the course edit page or a profile, I think it is more professional to display only new and upgraded themes in selectors instead of pretending old themes will work 100%. We have to make sure old themes will not cause fatal white screen errors.

Design overview

All theme files are served through two files /theme/styles.php and /theme/image.php. More advanced themes may serve extra javascript files through the /theme/javascripts.php file and a new config option with list of JS files. This approach allows us to parse the resulting CSS and replace all image placeholders and theme settings with current values.

All CSS style sheets (including YUI, plugin CSS and parent themes) are merged into a single large CSS file served via the /theme/styles.php file. This script accepts following parameters:

• theme (string) - name of the theme
• rev (int) - theme revision number stored in $CFG->themerevision

All options and features are reviewed and optimised. Backwards compatibility is not a primary concern, future possibilities and easy maintenance are always favoured.

Theme directory structure

File/folder'	'Description
db/ (optional)	Installation and upgrade hooks - use of db tables is not recommended.
lang/	Folder with standard language files - name of theme, usage information, settings. Standard themes store lang files in /lang/ for now.
layout/*.php	Folder with page layout templates
pix/	Folder with theme pictures - used from CSS or layout only, not used from other plugins.
pix_core/ (optional)	Folder with overridden core images and icons from /pix/ folder
pix_plugins/ (optional)	Folder with overridden plugin icons - structure is typeofplugin/pluginname/ which maps to pix folder in plugins
style/*.css	Style sheet files referenced from the config.php.
config.php	Theme configuration - see bellow.
lib.php (optional)	Library functions - custom css post-processing, custom render factory, theme init function
renderers.php (optional)	Custom renderers used from custom renderer factories.
settings.php (optional)	Custom theme settings - colours, logos, etc. Settings are applied in custom css post-processing function.
version.php	Needed for install and upgrade hooks, states compatibility with specific Moodle versions. Used for triggering of cache purging.

Theme config.php

The theme config.php structure is simplified and a bit more flexible. The goal is to make overriding of parent themes simple and easy to understand. Please note global $THEME variable is not available any more, use theme property in current page instance instead.

$THEME->parents = array('standard', 'purple'); Lists all parents top-down, each theme contains the full list of parents, this is non-recursive and more flexible specification without any limits. Originally the number of parent levels was restricted.

$THEME->sheets = array('styles_layout', 'styles_fonts', 'styles_color'); The same as before, lists files from current theme directory.

$THEME->parents_exclude_sheets('standard'=>array('styles_moz'), 'purple'=>array('styles_fonts')); It is also posssible to use true instead of array in order to specify all sheets or all sheets in all parents, if not specified the value from the parent theme is used.

$THEME->editor_sheets = array('styles_tinymce'); We can not load the full CSS file into the HTML editor's content area, instead we load editor sheet from lib/editor/editorname/editor_sheets.css and also sheets specified in theme.

$THEME->plugins_exclude_sheets('mod_book', 'gradereport_grader'); Ideally all plugin specific CSS should be stored in styles.css file separately in each plugin. This option lists plugins that should be excluded from this theme, if not specified the value from the parent theme is used.

$THEME->layouts = array(...); The complete list of layouts is in theme/base/config.php. Page layouts are in fact high level templates that are using PHP syntax. The template files are stored in layout/ subdirectory. Each page layout has specification of block areas and link to template file. Themes may also reference layouts files from other themes.

$THEME->resource_mp3player_colors, $THEME->filter_mediaplugin_colors Obsoleted. If not specified the value from the parent theme is used. All these should be moved to real theme settings.

$THEME->rendererfactory = 'standard_renderer_factory'; The same as before. It is the name of class that returns needed instances of core and plugin renderers. defined in core some library or theme/themename/lib.php or theme/themename/renderers.php

$THEME->csspostprocess = 'csspostprocess'; Name of custom CSS post-processing function, this function is usually defined in theme/themename/lib.php.

$THEME->javascripts = array('navigation'); $THEME->javascripts_footer = array('someJSlibrary'); List of extra javascript files that are included on each page. Themes can not include extra scripts from the theme folder because the folder may not be accessible via web.

Implementation

One huge CSS sheet

Each page includes only one huge style sheet. All theme sheets are served by a /theme/styles.php script. Page parameters specify the theme name and revision.

The CSS concatenation is done from the YUI CSS, styles.css from all plugins and theme style sheets starting with top most parent and current theme last, please note the order is very important. The algorithm is following:

1. YUI2 CSS
   1. merge all YUI2 CSS into one file, respect correct order of files
2. plugins CSS
   1. go through all plugins and search for styles.css - put the list into array, use component names as keys, locations as values
   2. filter out excluded sheets specified in current $THEME->plugins_exclude_sheets
3. theme CSS
   1. go through all sheets defined in all parents and store all $THEME->sheets in array
   2. filter out excluded sheets specified in current $THEME->parent_exclude_sheets
4. resolve real image locations
   1. regex search for [[pix:componentname|imagewithsibdirnoext]]
   2. priority is: current theme, parent themes, then plugin or YUI fodlers
   3. images in web accessible areas are linked directly, images in dataroot would have to go through /theme/image.php?theme=xxx&file=/sub/img&component=moodle&rev=-1
5. apply theme admin settings - values and image locations

Please note that the current $PAGE->requires->css() is suitable mostly for user supplied CSS for data content such as the custom CSS used in mod/data/ module.

The YUI3 reset CSS is loaded separated before this huge combined CSS stylesheet, YUI3 loader may load CSS on the fly from Javascript.

Theme caching

Potential problems are:

• server performance - the merging of all CSS, parent themes and image resolving is relatively expensive
• bandwidth - longer caching, fewer files and optional gzip compression
• stale data in browser caches - different file needs to be served when anything in CSS changes

The theme CSS content depends on:

• current theme
• theme revision

The theme revision is stored in $CFG->themerev, it is an integer counter incremented after installation/upgrade of any plugin or core. The revision value -1 is used in theme designer mode to prevent the caching completely.

All images used both from PHP and CSS have to be cached too. This is handled automatically in /theme/image.php which accepts similar parameters like the styles.php script.

The theme designer mode

Administrator, theme designers and developers often need to tweak CSS or images. In previous versions users had to purge the browser caches manually.

In theme designer mode no CSS is cached on server or in browser, each changes are immediately visible. The switching on of this mode immediately invalidates old caches, the caching is turned on again after switching it off. This mode causes higher server load.

This mode also disables all CSS cleanup and compression, all comments are kept and extra debug information can be included in CSS.

This setting is available from the Appearance settings page.

Performance improvements

There are several possibilities for more performance improvements:

• storing of final CSS files in dataroot - caches need to be deleted after each theme revision change; this could significantly reduce server load
• longer lifetimes - revision parameter eliminates the stale CSS in browser cache completely , lower bandwidth consumption
• gzip compression - faster page loading on first page
• remove comments and useless white space
• etc.

Browser hacks

Old meta.php was used mostly for conditional loading of IE specific hacks. Open University developed alternative solution which adds browser specific classes to body html element. This can be implemented in the pagelib method returning standard body tags.

<body class="ie ie7">

#mypage .whatever {
 /** normal rules */
}
.ie6#mypage .whatever {
 /** broken rules */
}

OU used these hacks not only for IE ;-)

RTL support

Originally RTL tweaks were stored in separate files. Now we use the same body class tweaks as described above.

<body class="dir-rtl">

#mypage .whatever {
 /** normal rules */
}
.dir-rtl #mypage .whatever {
 /** RTL rules */
}

YUI

Moodle started using YUI framework around 1.7, until 2.0dev we did not use any UI widgets that required CSS. The problem is that the YUI needs to be loaded before theme and plugin CSS, second problem is that standard YUI CSS requires reset CSS which greatly improves A-grade browser compatibility and helps theme designers.

YUI3 implements new loaders both for CSS and JS, there is a complementing PHP dependency loader for YUI.

YUI CSS foundation

Moodle styles are based on YUI foundation? Why not? The benefits are:

• eliminates some different HTML defaults (margins, paddings, font sizes, etc.) (YUI CSS Reset)
• consistent font sizing and better font-family degradation (YUI CSS Fonts)
• the standard YUI CSS is already built on top of this foundation
• incredibly simple table-less page layouts that include nesting (YUI CSS Grids) (optional, themes do not have to use it for layout)

YUI widgets customisation

The standard YUI CSS has to be loaded after YUI CSS Base (Reset+Fonts+Grids), but before our own CSS. Overriding of YUI stylesheets should not depend on the order of loading, we only guarantee that the YUI CSS foundation sheets are loaded before any other CSS, customisations of YUI skins has to use moodle class selectors.

YUI versioning

In 1.9 we store all YUI files in /lib/yui/ folder, this was a problem when upgrading to YUI version from upstream because the old files could be still cached in browsers.

In 2.0 we are finally replicating the YAHOO directory structures, each new version is stored in separate directory.

Combination of YUI 2 and 3

YUI 3 uses JS autoloading which is a great step forward and simplification. Unfortunately we still need the YUI2 libraries around for some time, luckily YUI2 libraries may coexist with YUI3 code.

The image resolver

Images are used in html code and in CSS style sheets. The problem is easy to solve in PHP code, partial solution was already present in Moodle 1.9 - see $CFG->pixpath

In 2.0dev there was implemented a new icon_finder class, it can be replaced by much simpler rules, we could also add pix support into all plugins.

Image locations:

• /mod/modulename/pix/, blocks/blockname/pix/ - in all plugins
• /theme/themename/pix/ - theme images
• /theme/themename/pix_core/ - overridden images from core /pix/ folder
• /theme/themename/pix_plugins/plugin/plugintype/ - overriding of plugin images in themes

The standard API is $OUTPUT->pix_url($componentname, $imagename, encoded) when used from PHP and [[pix:componentname|imagename]] if used in CSS.

Image resolved allows us to serve images from dataroot via /theme/image.php script and also solves all browser caching issues.

Themes in extra directory

Themes in dataroot is a frequently requested feature. Some admins might not like this, it should be optional. Some really advanced themes with lots of custom files might not be compatible at first. In fact it does not have to be dataroot, this location is configurable via $CFG->themedir.

In the stable branch we have a strange mix of standard themes. Moodle 2.0 is expected to include following themes:

• base - bare bones minimal theming that most other themes build on
• standard - basic theme that can be used as base for really simple themes (the exact look of new standard theme is not decided yet)
• customcolor - standard with admin specified colour palette and custom logos (not confirmed)
• and many other fancy modern themes like anomaly ( optionally with multiple configuration settings)

Other contrib themes could be available via web interface from Moodle configuration in some future Moodle version.

Admin theme settings

Very often users need to make small tweaks to standard themes such as different colour or logos. There should be a way to keep this settings in config_plugin and files separately in dataroot. Settings are placed in /theme/themename/settings.php. This new feature could significantly reduce known theme upgrade problems in the future.

This feature replaces the original CSS constants and will probably use the same syntax. The original CSS constants required modifications in dirroot which was in some cases unacceptable. CSS constants would not be compatible with automatic updates vie web interface anyway.

This feature requires advanced caching of CSS. These settings and files should be available in layouts and renderers too.

The actual replacing of setting placeholders by setting values is performed in custom css post-processing function specified in config.php. Logos and other custom images would be specified as external URLs, later we could also add basic support for storage of these custom theme files in standard Moodle filesystem.

Page layout

Each page may specify one of standard page layouts that are defined in theme/base/config.php. It is not possible to add custom layouts.

Layout definition consists of:

• template file specification - template name + file name without extension
• definition of regions
• default region

New layouts will not be added in the STABLE CVS branches.

Renderers

Renderers are small methods that render visual elements using functional programming - our old style PHP style.

Module may define own renderer class and use own renderer methods. Themes may override both core and plugin renderers however you need to have some more advanced understanding of PHP and Moodle design in general.

Templates (maybe in future)

Similar to page layouts but much smaller parts of UI that are embedded into pages. This is a new feature that is not used in Moodle core yet.

Code developers may choose to use templates instead of renderers for some larger parts of UI, they may also use renderers from templates. The major difference is that templates accept just one $DATA object with all parameters, templates might be also much easier to use&understand for typical theme designers.

The original emulated templates approach was replaced because it was designed for code developers, not designers. I think it is much easier to just copy templates from core or plugins into themes and tweak them, instead of the reverse engineering of the renderers.

Please note this does not mean that Moodle is switching to templates now, but technically we could, plugin developers would decide to do so independently. This topic should be revisited in Moodle 2.1dev.

Other API changes

• added course layout
• $PAGE->set_generaltype() replaced by $PAGE->set_pagelayout() because it really switches to one of the layouts from the standard theme; also the complete list of layouts is given in theme/standard/config.php - there is no way to add plugin layouts, the $PAGE->set_pagelayout() is used from core and plugin code, not from themes, so it is not possible to add new layouts at all (and never was)
• name things moodle_* only if potential conflicts exist, everything plugin related should be named componentname_ (mod_ is usually an exception)- this was discussed several times before; renamed moodle_core_renderer' class to core_renderer, etc.
• themes are now real plugins with capabilities, lang packs, upgrade code, settings, upgrade code, etc. - it is not recommended to create new db table though

Backwards compatibility and upgrades

BC is very limited, all themes and modules need to be manually updated. Keeping old themes during the upgrade must not cause fatal PHP errors. Old themes can be detected by searching for /theme/oldtheme/styles.php, this file will not be present in the new themes any more. Moodle core would simply use the specified parent theme or the standard theme.

Theme upgrade steps

1. delete styles.php
2. redefine all config.php options - in majority of cases change parent value to parents array
3. rename styles_ie6.css and styles_ie7.css to styles_layout_ie6.css and styles_layout_ie7.css - each normal sheet may have an extra sheet with _ieX suffix now, these are loaded automatically, excluding is applied based on $THEME->parents_exclude_sheets() info from the current theme
4. rename rtl.css to styles_layout_rtl.css - again each normal style sheet may have extra sheet with _rtl suffix similar to IE hacks sheets
5. delete header.html, footer.html and meta.php - obsoleted by $THEME->layouts option and new layout files
6. add custom layouts and rendereds

In order to minimize confusion during the upgrade, the old themes will be ignored and will be listed os "Incompatible" on the theme selection page - this page is probably the first place admins go in order to diagnose theme problems.

Module upgrade steps

• rename mod/modname/styles.php to styles.css
• put all images into mod/modname/pix/
• replace $CFG->pixpath with $OUTPUT->pix_url('imagename', 'mod_modname')

Removed features

1. sometheme/meta.php - used mostly for IE6/7 hacks, custom layouts may be used instead
2. smartpix - completely obsoleted by the new image location resolution algorithm
3. styles.php replaced by styles.css, supported in all plugin types - the PHP syntax is not needed anymore because images are specified using [[pix:component|dir/image]] syntax and we can also use custom css post-processors
4. $CFG->pixpath replaced by $OUTPUT->pix_url()
5. CSS constants replaced by the admin theme settings
6. separate IE6 and IE7 sheets - replaced by body class attributes
7. separate RTL sheets - replaced by body class attribute

Expected reactions

User type	Negative	Positive
Core developer	none	No backwards compatibility headaches. Powerful new features. More flexible API.
Contrib developer	Has to learn new API and upgrade current code.	New useful pix folder and standard styles.css in all plugins. $OUTPUT->pix_url() more flexible then old pixpath.
Theme designer	Has to learn new theme API. Old advanced themes has to be completely redesigned. Has to understand YUI CSS foundation.	They can finally override core and plugin images. Easier distribution of custom themes. New income opportunity. Basic theme structure is simplified. No browser caching issues when designing themes.
Administrator	All themes need to be updated. Old themes are ignored.	Much easier installation (optionally in dataroot) and easy customisation without code modification (images and colours for example). Much safer upgrades. Possibility to upgrade theme via web interface. No browser caching issues when upgrading themes. Better performance and lower server load.

See also

Using Moodle forum discussions:

• Yet more theme changes proposal
• HEADS UP: Major theme changes landing
• Development:Output_renderers