Bug 212688 – [Win] Some Tibetan characters aren't shown

• Status: NEW
• Component: Platform

[Fujii Hironori]

[Win] Some Tibetan characters aren't shown

Both AppleWin and WinCairo have the issue.

https://unicode.org/charts/nameslist/c_0F00.html
https://ja.wikipedia.org/wiki/%E3%83%81%E3%83%99%E3%83%83%E3%83%88%E8%AA%9E

[Fujii Hironori]

Created attachment 400906 [details]
[Screenshot] WinCairo port

[Fujii Hironori]

Created attachment 400907 [details]
DOTTED CIRCLE + TIBETAN ASTROLOGICAL SIGN SDONG TSHUGS

[Fujii Hironori]

FontCache::systemFallbackForCharacters of FontCacheWin.cpp is
using three steps to choose a fallback font.

1. Try IMLangFontLink::MapFont method
2. If no font found, try meta file method
3. If no font found, try FontLink registry method

For the missing Tibetan characters, IMLangFontLink::MapFont
method returns "Arial Unicode MS" font, but Uniscribe returns
USP_E_SCRIPT_NOT_IN_FONT for the font.

For other Tibetan characters, IMLangFontLink::MapFont method
returns "Microsoft Himalaya" font

[Fujii Hironori]

Following StackOverflow suggests reffering Chromium's render_text_win.cc.

How to automatically choose most suitable font for different language? - Stack Overflow
https://stackoverflow.com/q/16828868

Check if Unicode character is displayed or tofu - Stack Overflow
https://stackoverflow.com/q/47840800

Chromium UI was using Uniscribe, but it was replaced by HarfBuzz.

https://codereview.chromium.org/891013003

https://chromium.googlesource.com/chromium/src.git/+/2e9885788692f69203a98fb42347428ef553d640/ui/gfx/render_text_win.cc
https://chromium.googlesource.com/chromium/src.git/+/2e9885788692f69203a98fb42347428ef553d640/ui/gfx/font_fallback_win.cc

[Fujii Hironori]

Created attachment 401504 [details]
[Screenshot] WinCairo (after r262804)

r262804 (Bug 212947) changed the situation. After the change,
some Tibetan characters start to show while combining marks still
doesn't render correctly.

[Fujii Hironori]

Created attachment 401505 [details]
[Screenshot] Tibetan Wikipedia in WinCairo (after r262804)

Tibetan pages look broken.
https://bo.wikipedia.org/

[Fujii Hironori]

I'm going to try stop using MLang font linking in the following ticket.
Bug 213008 – [Win] Stop using MLang font linking for system font fallback