RFR: 8246104: Some complex text doesn't render correctly on macOS [v10]

[Phil Race]

> This PR addresses some font problems on macOS.
> (1) Garbled Arabic with the System font
> (2) Non-ideal fallback fonts for all fonts
> (3) No bold for System font.
> 
> In particular the standard System Font was garbling Arabic text - random glyphs from another font.
> The root of this issue is that several releases ago macOS introduced UI fonts that are hidden from
> enumeration. must be loaded by a special API and cannot be loaded by name, even if you extract
> the name from the core text font loaded by that special API.
> These fonts usually have a name that begins with "." such as the postscript name ".AppleUISystemFont"
> and "name" for the main instance of this will be "System Font Regular". These live in files called "SFNS.ttf"
> and "SFArabic.ttf" and similar.
> 
> JavaFX has its own "System" font family logical name and in order to map to the macOS system font,
> several releases ago we started using the special API referenced above.
> 
> Normally we have our own list of fall back fonts for other scripts.
> But when we encounter complex scripts such as Arabic, and ask CoreText to layout the glyphs,
> it may use other system fonts for Arabic (eg ".SFArabic") and the FX code dynamically adds
> this new font to its fallback list - by name.
> But this new font can't be directly referenced by name either, but that's what used to work and the FX code tries.
> 
> So to fix this we need to grab the reference to the font that was returned by CoreText and use
> that to create the PrismFont we add as a fall back.
> The code that first recognises it needs to go this route is in CTGlyphLayout.java when
> "getSlotForFont(String name") fails.
> Instead it calls new code in CTFactory which in turn calls a new constructor and supporting code in CTFontFile.java.
> There's also supporting changes in native code - coretext.c
> 
> Additionally to support that when we ask the platform to enumerate fallbacks, we might get such "." fonts,
> we need to make some more changes
> Now on to more "fallback" enhancements.
> Prior to this fix, on macOS we had a short, hard-coded global list.
> This fix calls the macOS API to get the cascading fallback list for a font.
> This improves the fallback behaviour in respect to providing
> (1) More appropriate styles, (2) More supported code pointd, (3) Code point support coming from a preferred font.
> There was some desirable re-factoring as part of this, as the location of fallbacks was pushed from
> "if <windows> else if <linux> else <mac> in shared code, down into the appropriate platform factory
> 
> This also made it easier to do some required changes to allow fallbacks to be pre-initialised with the
> native font resource, not just a name+ file. The new class FontFallbackInfo encapsulates this and changes
> were made to follow it.
> In practice on macOS it seems that some "." cascading fallbacks for the "." system font come with a "NULL"
> file name. Without being able to identify the file we aren't able to use the font to skip them.
> More changes would be needed to provide a PrismFont subclass that can handle this case.
> Fortunately that isn't happening for any of the fallbacks we get from complex text layout.
> 
> The final thing this fixes is that "System Bold" was the same as "System Regular".
> The needed name getting lost along the way to constructing the native font.
> 
> The work done here also highlighted that we really need to add code that at least recognises OpenType variation fonts.
> And some day after that we could expose API that allows apps to request non-named variations.

Phil Race has updated the pull request incrementally with one additional commit since the last revision:

  Fix formatting and NPE

-------------

Changes:
  - all: https://git.openjdk.org/jfx/pull/1067/files
  - new: https://git.openjdk.org/jfx/pull/1067/files/0a1104ef..c11bf1cb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1067&range=09
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1067&range=08-09

  Stats: 6 lines in 2 files changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1067.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1067/head:pull/1067

PR: https://git.openjdk.org/jfx/pull/1067