Make an HBFont from a CTFontRef.

By including ```rive/text/font_hb.hpp``` in iOS you'll get access to ```HBFont::FromSystem``` along with the ```HBFont::Decode``` (which we've been using so far to generate Font objects to put into the fallback list).

You can get a UIFont with [this API](https://developer.apple.com/documentation/uikit/uifont/1619027-systemfontofsize?language=objc).

You should be able to cast that to a CTFontRef:
```
CTFontRef ctFont = (__bridge CTFontRef)uiFont;
auto fallbackFont = HBFont::FromSystem((void*)ctFont);
```

You can then use that in a fallback font procedure (like the example from the editor below) to load on demand/cache/provide from a list etc:
https://github.com/rive-app/rive/blob/b5b930f88f18280afa44683c5756066abaa9b1dc/packages/rive_common/macos/rive_text/rive_text.cpp#L153-L175

Diffs=
da1bb7745 Make an HBFont from a CTFontRef. (#7661)

Co-authored-by: Luigi Rosso <luigi-rosso@users.noreply.github.com>

.rive_head

@@ -1 +1 @@
-1a5f273bb6534a395d1c3cdcc11a1ba3cd80a96c
+da1bb77455deeafd48012a8eea5ea946a718fb77

build/premake5.lua

@@ -128,6 +128,11 @@ do
         objdir('%{cfg.system}_sim/obj/%{cfg.buildcfg}')
     end
 
+    filter('system:macosx or system:ios')
+    do
+        files({ '../src/text/font_hb_apple.mm' })
+    end
+
     filter({ 'system:android', 'configurations:release' })
     do
         buildoptions({ '-flto=full' })

dependencies/premake5_harfbuzz.lua

@@ -349,4 +349,10 @@ do
         targetdir('%{cfg.system}/cache/arm64/bin/%{cfg.buildcfg}')
         objdir('%{cfg.system}/cache/arm64/obj/%{cfg.buildcfg}')
     end
+
+    filter('system:macosx or system:ios')
+    do
+        defines({'HAVE_CORETEXT'})
+        files({harfbuzz .. '/src/hb-coretext.cc'})
+    end
 end

dependencies/premake5_harfbuzz_v2.lua

@@ -274,4 +274,10 @@ do
         includedirs({ './' })
         forceincludes({ 'rive_harfbuzz_renames.h' })
     end
+
+    filter('system:macosx or system:ios')
+    do
+        defines({'HAVE_CORETEXT'})
+        files({harfbuzz .. '/src/hb-coretext.cc'})
+    end
 end

dev/test/premake5.lua

@@ -62,4 +62,13 @@ do
         })
         forceincludes({ 'rive_yoga_renames.h' })
     end
+
+    filter({ 'system:macosx'} )
+    do
+        links({
+            'Foundation.framework',
+            'CoreGraphics.framework',
+            'CoreText.framework'
+        })
+    end
 end

include/rive/text/font_hb.hpp

@@ -32,6 +32,7 @@ class HBFont : public rive::Font
     bool hasGlyph(rive::Span<const rive::Unichar>) const override;
 
     static rive::rcp<rive::Font> Decode(rive::Span<const uint8_t>);
+    static rive::rcp<rive::Font> FromSystem(void* systemFont);
     hb_font_t* font() const { return m_font; }
 
 private:

premake5_v2.lua

@@ -140,6 +140,11 @@ do
         architecture('x64')
         defines({ '_USE_MATH_DEFINES' })
     end
+
+    filter('system:macosx or system:ios')
+    do
+        files({ 'src/text/font_hb_apple.mm' })
+    end
 end
 
 newoption({
@@ -177,4 +182,4 @@ newoption({
 newoption({
     trigger = 'with_rive_layout',
     description = 'Compiles in layout features.',
-})
+})

src/text/font_hb.cpp

@@ -48,6 +48,10 @@ rive::rcp<rive::Font> HBFont::Decode(rive::Span<const uint8_t> span)
     return nullptr;
 }
 
+#ifndef __APPLE__
+rive::rcp<rive::Font> HBFont::FromSystem(void* systemFont) { return nullptr; }
+#endif
+
 //////////////
 
 constexpr int kStdScale = 2048;

src/text/font_hb_apple.mm

@@ -0,0 +1,18 @@
+#include "rive/text_engine.hpp"
+
+#ifdef WITH_RIVE_TEXT
+#include "rive/text/font_hb.hpp"
+#import <CoreText/CoreText.h>
+
+#include "hb-coretext.h"
+
+rive::rcp<rive::Font> HBFont::FromSystem(void* systemFont)
+{
+    auto font = hb_coretext_font_create((CTFontRef)systemFont);
+    if (font)
+    {
+        return rive::rcp<rive::Font>(new HBFont(font));
+    }
+    return nullptr;
+}
+#endif