1212731 - implement font cascading for system fonts under OSX

Status: REOPENED

(Core :: Graphics: Text, defect, P3)

Description

[John Daggett (:jtd)]

To pick up non-Latin UI fonts under OSX we need to implement support for system font cascade-based fallback.

While working on supporting system fonts under OSX 10.11 in bug 1201318, I noticed that we don't really handle system fonts correctly across locales. When the user locale is set to Japanese for example, the system font API's (i.e. [NSFont systemFontOfSize:0.0]) still return a Latin font (e.g. Lucida Grande, Helvetica Neue, San Francisco). This means that UI picks up the default font from pref font lists. This is not really the system defined way of doing this.

The OSX way of doing this correctly is to use a system-provided "cascade list", basically an array of font descriptors representing fonts that should be used as fallback for a particular font. For system fonts, this will include hidden system fonts for which there's no other way to look them up.

Pseudo code for this:

  get system font
  get default cascade for system font (e.g. CTFontCopyDefaultCascadeList(systemFont))
  add to a new attributes dictionary, with key kCTFontCascadeListAttribute
  create a font descriptor, then a new font
  use CTFontCreateForString(new font, str) to determine the fallback font

In terms of the font matching process, normally we choose a font based on:

  fontlist ==> pref fonts ==> system-wide fallback

For this case, we need to use the system font cascade *before* pref fonts:

  fontlist ==> cascade ==> pref fonts ==> system-wide fallback

There's one ripple here and that is that defualt system cascade is hard-coded to prioritize Japanese fonts over Chinese fonts. This is a problem for zh-Hans and zh-Hant locales. There's a private CoreText API for this purpose:

  // prioritize zh-Hant fonts over ja fonts
  CFStringRef langs[1] = { CFSTR("zh-Hant") };
  langList = CFArrayCreate(kCFAllocatorDefault, (const void **) langs, 1, &kCFTypeArrayCallBacks);
  CFArrayRef cascade = CTFontCopyDefaultCascadeListForLanguages(systemFont, langList);

This is important to pick up .Hiragino Kaku Gothic Interface for Japanese and .Apple SD Gothic NeoI for Korean on OSX 10.11:

[.Hiragino Kaku Gothic Interface] .HiraKakuInterface-W0 -0.80 0.00 0.00 80000000
[.Hiragino Kaku Gothic Interface] .HiraKakuInterface-W1 -0.60 0.00 0.00 80000000
[.Hiragino Kaku Gothic Interface] .HiraKakuInterface-W2 -0.40 0.00 0.00 80000000
[.Hiragino Kaku Gothic Interface] .HiraKakuInterface-W3 0.00 0.00 0.00 80000000
[.Hiragino Kaku Gothic Interface] .HiraKakuInterface-W4 0.23 0.00 0.00 80000000
[.Hiragino Kaku Gothic Interface] .HiraKakuInterface-W5 0.30 0.00 0.00 80000002
[.Hiragino Kaku Gothic Interface] .HiraKakuInterface-W6 0.30 0.00 0.00 80000002
[.Hiragino Kaku Gothic Interface] .HiraKakuInterface-W7 0.56 0.00 0.00 80000002
[.Hiragino Kaku Gothic Interface] .HiraKakuInterface-W8 0.62 0.00 0.00 80000002
[.Hiragino Kaku Gothic Interface] .HiraKakuInterface-W9 0.62 0.00 0.00 80000002

[.Apple SD Gothic NeoI] .AppleSDGothicNeoI-Bold 0.00 0.00 0.00 80000000
[.Apple SD Gothic NeoI] .AppleSDGothicNeoI-ExtraBold 0.00 0.00 0.00 80000000
[.Apple SD Gothic NeoI] .AppleSDGothicNeoI-Heavy 0.00 0.00 0.00 80000000
[.Apple SD Gothic NeoI] .AppleSDGothicNeoI-Light 0.00 0.00 0.00 80000000
[.Apple SD Gothic NeoI] .AppleSDGothicNeoI-Medium 0.00 0.00 0.00 80000000
[.Apple SD Gothic NeoI] .AppleSDGothicNeoI-Regular 0.00 0.00 0.00 80000000
[.Apple SD Gothic NeoI] .AppleSDGothicNeoI-SemiBold 0.00 0.00 0.00 80000000
[.Apple SD Gothic NeoI] .AppleSDGothicNeoI-Thin 0.00 0.00 0.00 80000000
[.Apple SD Gothic NeoI] .AppleSDGothicNeoI-UltraLight 0.00 0.00 0.00 80000000

Comment 1

[John Daggett (:jtd)]

Attachment: sample code for doing cascade-based font fallback

Sample code based on Jiang Jiang's fallback.m and Webkit private CoreText API usage.

https://gist.github.com/jjgod/4296416b06b39ef49206

Comment 2

[John Daggett (:jtd)]

Attachment: patch p1 - move GetSampleLangForGroup into base class

Comment 3

[John Daggett (:jtd)]

Attachment: patch p2 - add system font cascade to fontlist for -apple-system generic

Comment 4

[John Daggett (:jtd)]

Attachment: patch p3 - reftests for system font cascade

Comment 5

[Makoto Kato [:m_kato]]

Comment on attachment 8708198 [details] [diff] [review]
patch p2 - add system font cascade to fontlist for -apple-system generic

Review of attachment 8708198 [details] [diff] [review]:
-----------------------------------------------------------------

::: gfx/thebes/gfxFontEntry.h
@@ +796,5 @@
>      void SetSkipSpaceFeatureCheck(bool aSkipCheck) {
>          mSkipDefaultFeatureSpaceCheck = aSkipCheck;
>      }
>  
> +    bool LinkedSystemFamily() { return mLinkedSystemFamily; }

bool LinkedSystemFamily() const { ... }

::: gfx/thebes/gfxMacPlatformFontList.h
@@ +107,5 @@
>                            float aDevPixPerCSSPixel);
>  
> +    void
> +    AppendLinkedSystemFamilies(nsIAtom* aLanguage,
> +                               nsTArray<gfxFontFamily*>& aFamilyList) override;

virtual void ...

::: gfx/thebes/gfxMacPlatformFontList.mm
@@ +804,5 @@
> +    CTFontRef systemFont =
> +        CTFontCreateUIFontForLanguage(kCTFontSystemFontType, 12.0,
> +                                      CFSTR("en-US"));
> +
> +    nsAutoCString lang(aLang);

Remove "nsAutoCString lang(aLang);" because lang uses one time only.

@@ +809,5 @@
> +
> +    // fetch cascade list
> +    CFStringRef langStr =
> +        CFStringCreateWithCString(kCFAllocatorDefault, lang.get(),
> +                                  kCFStringEncodingUTF8);

Change to CFStringCreateWithCString(kCFAllocatorDefault, PromiseFlatCString(aLang).get(), ...

Comment 6

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/f6c4b1a37957
https://hg.mozilla.org/integration/mozilla-inbound/rev/e3d9e10c19f9
https://hg.mozilla.org/integration/mozilla-inbound/rev/309e36d57832

Comment 7

[Ryan VanderMeulen (PTO, back 6-April)]

https://hg.mozilla.org/mozilla-central/rev/f6c4b1a37957
https://hg.mozilla.org/mozilla-central/rev/e3d9e10c19f9
https://hg.mozilla.org/mozilla-central/rev/309e36d57832

Comment 8

[John Daggett (:jtd)]

Because of the regression in bug 1244017, I backed out the support for the system font cascade. Any re-implementation will need to figure out the details of when and how to apply the system font cascade, as it appears that Safari is not using this in precisely the same way. For example, full-width digits are pulled from Apple Symbols when using the system font cascade fallback order but from Hiragino Kaku Gothic Pro when using our existing fallback.

The startup regression can probably be resolved by initializing the system font cascade on a separate thread. This will give slightly different UI rendering for the first few seconds after startup but I doubt this will make much of a difference for CJK locales.