Manual:Coding conventions/SVG

This page describes the coding conventions used within files of the MediaWiki codebase written in SVG. See also the general conventions that apply to all programming & markup languages, including SVG.

On per-project base we make use of [ https://github.com/svg/svgo SVGO] as optimisation tool, see automated optimisation below. Another helpful tool for further optimisation are:


 * 1) SvgWorkAroundBot
 * 2) SVGOMG
 * 3) scour
 * 4) svgcleaner
 * 5) check Help:SVG guidelines#How to optimize for more options.

Code structure
Minimal code as possible with readability in mind is the premise.

Example for simple optimised file – subtract.svg from OOUI:

For minimalists, exactly the same can be drawn with

Example for slightly more complex, optimised file – BetaFeatures screenshot template:

We will explain the different coding conventions in the following section.

Automated optimisation (SVGO)
A standard set of conventions can be enforced by help of SVGO. If your original SVGs are well-formed, you should be able to automatically optimise them. As some SVGO default plugins (options) might result in unexpected appearance with more complex SVGs, we differentiate between safe, considerably less-safe and unsafe plugins. When using unsafe plugins it's recommended to verify before and after diffing per file to ensure visual quality.

Safe plugins:

Mentioning only plugins, that are changed from default setting or that might be counter-intuitive:

See SVGO Readme for other enabled, safe plugins.
 * Sorting attributes 'sortAttrs' Enable by setting to  ; disabled by default
 * Remove or cleanup  attribute when possible 'cleanupEnableBackground' Deprecated attribute, only supported by IE/Edge; enabled by default

Plugins to consider carefully:


 * Remove unused and minify used IDs 'cleanupIDs' Might negatively affect readability ; enabled by default
 * Remove raster images 'removeRasterImages' As general rule dangerous, could cause data loss, some raster-images are difficult to spot ; disabled by default
 * convertShapeToPath can reduce readability
 * inlineStyles some users prefer to use CSS than inlineStyles, can reduce editability
 * removeDoctype for SVG 1.1 there is not reason to remove it, however for the upcommong SVG2-draft it will be deapreciated

Unsafe rules to disable (don't use!):


 * Round/rewrite number lists 'convertPathData' Might cause (i) imprecise rendering, (ii) wrong rendering by librsvg, (iii) breaking files ; enabled by default
 * Remove XML processing instructions 'removeXMLProcInst', aka XML declaration  Issues when viewed as standalone file in some editors, also possible issues with MIME type interpretation Example: If the SVG doesn't start with an XML declaration, then it's MIME type will be detected as   rather than   by libmagic and consequently, MediaWiki's CSSMin CSS minifier. libmagic's default database currently requires that SVGs contain an XML declaration; disable by setting to  ; enabled by default
 * Remove 'removeTitle' Problematic for accessibility reasons ; set to  ; enabled by default
 * Remove 'removeDesc' Problematic for accessibility reasons; set to  ; enabled by default
 * Remove  attribute 'removeViewBox' Results in troublesome appearance in some browsers, therefore both,  /  and   should be featured; set to  ; enabled by default
 * Remove dimensions /  when   is available 'removeDimensions' As above; set to  ; disabled by default
 * removeMetadata Possible Copyright-Information
 * removeHiddenElems Possible reference lines, editor data, real text before convertion, Copyright-informations
 * removeUnknownsAndDefaults removes Flow-Text
 * cleanupNumericValues breaks some files
 * minifyStyles breaks some files
 * removeComments reduces readability and possible removes reference lines, editor data, real text before convertion, Copyright-informations
 * removeEditorsNSData reduces editability with GUI-SVG-Editors
 * collapseGroups reduced readabilty and editability
 * removeStyleElement breaks some files

Exemplified safe configuration
Note that this is for svgo v1.x; v2.x takes different CLI arguments:

Use  output for human readable code and in the process indent code by tabs.

Exemplified safe configuration ( .svgo.config.js )
Update Jan 2022: NPM run scripts enabled SVGO configuration (T246321).

Exemplified safe configuration ( Gruntfile.js )
svgmin: { options: { js2svg: { indent: '\t', pretty: true },		plugins: [ { cleanupIDs: false }, {			removeDesc: false }, {			removeRasterImages: true }, {			removeTitle: false }, {			removeViewBox: false }, {			removeXMLProcInst: false }, {			sortAttrs: true } ]	} }

Manual optimisation
Beyond automated optimising SVGs there are further steps to consider:


 * retain the following code,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  , see c:Help:SVG guideline
 * Remove  from XML processing instruction, as it's default
 * Lowercase (for better gzipping) and shorten hex color values, if possible, e.g.  instead of.
 * Attributes that are the same for a group of elements can be applied to a common parent instead,
 * or sometimes even specified by the  statement (see an example: CHE Bettens COA.svg).


 * Rely on defaults like  and.
 * The  syntax is almost always shorter than the syntax of basic shapes like  or even . The only possible exceptions are, , and rounded  , as converting them to paths typically results in sequences of long floating point numbers.
 * Merge  elements where applicable.
 * Remove redundant  attribute when identical to   as renderer must consider both values identical when one's missing.
 * Remove not needed  and  . These rules only have an effect on certain paths, e.g. when a path intersects itself.
 * Look for IEEE rounding errors like  or  . Such numbers take up space without providing any additional information. They can almost always be cut off without visually changing anything.
 * Work with a non-fractional pixel grid while drawing, and align as much points as possible on this grid. These points have a much higher chance of being represented as short integer numbers in the resulting code.
 * Pick a non-fractional grid so that it matches the features of an existing image, and scale or redraw shapes so that as many points as possible fall on the grid. The result might be misaligned and can be cropped using.

If you want to dig even deeper, there are more optimisations to compress delivery, such as:


 * auto-closing paths (aka removing  for certain shapes),
 * use relative commands when creating paths (instead of absolute commands, e.g. "m" for "move by", instead of "M" for "move to"),
 * optimising for compression backreferences