[ios,macos] Darwin implementation of a CoreText-based LocalGlyphRasterizer.

- Changing font weight does not currently appear to be working.
 - Glyph metric extraction code not working; currently unused.

src/mbgl/renderer/renderer.cpp

@@ -10,9 +10,10 @@ Renderer::Renderer(RendererBackend& backend,
                    FileSource& fileSource_,
                    Scheduler& scheduler_,
                    GLContextMode contextMode_,
-                   const optional<std::string> programCacheDir_)
+                   const optional<std::string> programCacheDir_,
+                   const optional<std::string> localFontFamily_)
         : impl(std::make_unique<Impl>(backend, pixelRatio_, fileSource_, scheduler_,
-                                      contextMode_, std::move(programCacheDir_))) {
+                                      contextMode_, std::move(programCacheDir_), std::move(localFontFamily_))) {
 }
 
 Renderer::~Renderer() {

src/mbgl/renderer/renderer_impl.cpp

@@ -42,7 +42,8 @@ Renderer::Impl::Impl(RendererBackend& backend_,
                      FileSource& fileSource_,
                      Scheduler& scheduler_,
                      GLContextMode contextMode_,
-                     const optional<std::string> programCacheDir_)
+                     const optional<std::string> programCacheDir_,
+                     const optional<std::string> localFontFamily_)
     : backend(backend_)
     , scheduler(scheduler_)
     , fileSource(fileSource_)
@@ -50,7 +51,7 @@ Renderer::Impl::Impl(RendererBackend& backend_,
     , contextMode(contextMode_)
     , pixelRatio(pixelRatio_)
     , programCacheDir(programCacheDir_)
-    , glyphManager(std::make_unique<GlyphManager>(fileSource))
+    , glyphManager(std::make_unique<GlyphManager>(fileSource, std::make_unique<LocalGlyphRasterizer>(localFontFamily_)))
     , imageManager(std::make_unique<ImageManager>())
     , lineAtlas(std::make_unique<LineAtlas>(Size{ 256, 512 }))
     , imageImpls(makeMutable<std::vector<Immutable<style::Image::Impl>>>())

src/mbgl/renderer/renderer_impl.hpp

@@ -38,7 +38,7 @@ class Renderer::Impl : public GlyphManagerObserver,
                        public RenderSourceObserver{
 public:
     Impl(RendererBackend&, float pixelRatio_, FileSource&, Scheduler&, GLContextMode,
-         const optional<std::string> programCacheDir);
+         const optional<std::string> programCacheDir, const optional<std::string> localFontFamily);
     ~Impl() final;
 
     void markContextLost() {

src/mbgl/text/glyph_manager.hpp

@@ -25,7 +25,7 @@ public:
 
 class GlyphManager : public util::noncopyable {
 public:
-    GlyphManager(FileSource&, std::unique_ptr<LocalGlyphRasterizer> = std::make_unique<LocalGlyphRasterizer>());
+    GlyphManager(FileSource&, std::unique_ptr<LocalGlyphRasterizer> = std::make_unique<LocalGlyphRasterizer>(optional<std::string>()));
     ~GlyphManager();
 
     // Workers send a `getGlyphs` message to the main thread once they have determined

src/mbgl/text/local_glyph_rasterizer.hpp

@@ -32,11 +32,15 @@ namespace mbgl {
 
 class LocalGlyphRasterizer {
 public:
-    virtual ~LocalGlyphRasterizer() = default;
+    virtual ~LocalGlyphRasterizer();
+    LocalGlyphRasterizer(const optional<std::string> fontFamily = optional<std::string>());
 
     // virtual so that test harness can override platform-specific behavior
     virtual bool canRasterizeGlyph(const FontStack&, GlyphID);
     virtual Glyph rasterizeGlyph(const FontStack&, GlyphID);
+private:
+    class Impl;
+    std::unique_ptr<Impl> impl;
 };
 
 } // namespace mbgl

src/mbgl/util/i18n.cpp

@@ -392,6 +392,11 @@ bool allowsIdeographicBreaking(char16_t chr) {
     //        || isInCJKCompatibilityIdeographsSupplement(chr));
 }
 
+bool allowsFixedWidthGlyphGeneration(char16_t chr) {
+    // Mirrors conservative set of characters used in glyph_manager.js/_tinySDF
+    return isInCJKUnifiedIdeographs(chr) || isInHangulSyllables(chr);
+}
+
 bool allowsVerticalWritingMode(const std::u16string& string) {
     for (char32_t chr : string) {
         if (hasUprightVerticalOrientation(chr)) {

src/mbgl/util/i18n.hpp

@@ -23,6 +23,10 @@ bool allowsIdeographicBreaking(const std::u16string& string);
     by the given Unicode codepoint due to ideographic breaking. */
 bool allowsIdeographicBreaking(char16_t chr);
 
+/** Conservative set of characters expected to have relatively fixed sizes and
+    advances */
+bool allowsFixedWidthGlyphGeneration(char16_t chr);
+
 /** Returns whether any substring of the given string can be drawn as vertical
     text with upright glyphs. */
 bool allowsVerticalWritingMode(const std::u16string& string);