Extension:UniversalLanguageSelector/Fonts for Chinese wikis

Introduction
Including all Chinese characters makes a webfont file too large. We may want to tailor the font file for every page based on characters used on that page. Once finished, this feature can be applied to other languages facing the same problem, such as Japanese.

As of writing, there isn't any "good" enough free font which includes all Chinese characters in Unicode. And the "wiki" concept itself encourages collaborative content creation, so it would be nice to invite user to create a glyph for it when the system sees a character without existing data.

Proposal
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Mentors
DChan,  Liangent

Repository
Font Tailor

Tofu Detection

Development_Report
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Milestones

 * May 19: Start coding.
 * Warm up with code and development tool set
 * Clarify what to do next
 * June 22: Mid-term evaluation: Finish the prototype of Font Tailor
 * July 20: Finish the Font Tailor ( ttf tailor finished and well tested. svg/woff/eot tailor finished but with no guarantee )
 * Aug 11: Pencil down: Tofu detection with font family settings
 * < - - - We are here
 * Aug 22: Final evaluation: Documents and final-term report

Dynamic WebFonts
For standard WebFonts service, a static font file is downloaded. The @font-face rule is like: @font-face { font-family: WenQuanYi; ...   src: url('fontspath/wenquanyi.ttf') format('ttf'), ...; } Now we should return different font which is well tailored to contain all / only the characters in that page. So we change the url to: @font-face { font-family: WenQuanYi; ...   src: url('FontRequest.php?font=WenQuanYi...') format('ttf'), ...; } When the page is visited, a font request will be fired towards FontTailor.php. The php will get enough information from the parameters. If a tailored font file exists and is up-to-date, return it by attachment: header( "Content-Type: application/octet-stream" ); header( "Content-Disposition: attachment; filename=\"$wanted_filename\"" ); readfile( $tailored_fontfile ); If no tailored font file is available or it is out dated, the php should generate one.

Font Tailor
The FontTailor.php gets to know three parameters: FontTailor will get the content of the source page, and get the set of characters in use. Then generate a subset of the font file. Currently we use php-font-lib to tailor TTF / WOFF / EOT. And write another SVG tailor by cutting the SVG xml dom tree. But only TTF tailor is tested up to now.
 * 1) Which page is requesting WebFonts? - We can get this in $_SERVER['HTTP_REFERER'] generally.
 * 2) Which font is requested? - Get from url parameters.

Known Issues
Currently I use php's curl to get the page content. I think there may be a way to read the DB directly. Check APIs for it later.
 * Get wiki page content from the database, while not fire a HTTP request

It's strange that the output font file cannot work in WebFonts. But if you read it by another font editor ( FontCreater or FontForge ), and save to another file, it will work. You can find that the two files have some difference. I don't know why, yet. If someone have knowledge on TTF fonts, please take a look:
 * php-font-lib bug

- Output TTF of php-font-lib

- Fixed TTF by FontForge

Current solution is to run another fix function: Open('input.ttf',1) SelectAll Copy Generate('output.ttf') Close It's ugly to call exec in PHP, and it's also ugly to have fontforge required. So I want to fix the problem in php-font-lib if possible.
 * 1) !/usr/bin/env fontforge

Tofu Detection with FontFamily
If a Chinese character is rendered as a tofu, the reason is obviously that the glyph is not available in the fonts, both from WebFonts service or from the system. According to, the most reliable way to detect a tofu is to compare it's image with the known tofu's image, such as unicode 0x0D00.

However, you cannot do that with a fixed fontFamily like sans-serif, because a WebFonts service may render it properly with the remote fonts. So the current detectTofu method may get some false-positive error. We should detect tofu with it's real fontFamily setting. And tofus are different, too. As you see below:
 * &#x0d00; [sans-serif tofu]
 * &#x0d00; [Linux Libertine tofu]
 * &#x0d00; [宋体 tofu]
 * &#x0d00; [Georgia tofu]

Detect Tofu by Comparing Image
Use HTML5's canvas element to draw each character, and compare with the tofu's image.

It's introduced in another patch from me, see and patch 122277.

Popup to Show Tofu Information
// TODO