1 files changed, 42 insertions, 0 deletions
diff --git a/src/mbgl/text/local_glyph_rasterizer.hpp b/src/mbgl/text/local_glyph_rasterizer.hpp
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index 0000000000..c2bdbd2840
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+++ b/src/mbgl/text/local_glyph_rasterizer.hpp
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+#pragma once
+
+#include <mbgl/text/glyph.hpp>
+
+namespace mbgl {
+
+/*
+    Given a font stack and a glyph ID, platform-specific implementations of
+    LocalGlyphRasterizer will decide which, if any, local fonts to use and
+    then generate a matching glyph object with a greyscale rasterization of
+    the glyph and appropriate metrics. GlyphManager will then use TinySDF to
+    transform the rasterized bitmap into an SDF.
+ 
+    The JS equivalent of this functionality will only generate glyphs in the
+    'CJK Unified Ideographs' and 'Hangul Syllables' ranges, for which it can
+    get away with rendering a fixed 30px square image and GlyphMetrics of:
+
+        width: 24,
+        height: 24,
+        left: 0,
+        top: -8,
+        advance: 24
+
+    The JS equivalent also uses heuristic evaluation of the font stack name
+    to control the font-weight it uses during rasterization.
+ 
+    It is left to platform-specific implementation to decide how best to
+    map a FontStack to a particular rasterization.
+ 
+    The default implementation simply refuses to rasterize any glyphs.
+*/
+
+class LocalGlyphRasterizer {
+public:
+    virtual ~LocalGlyphRasterizer() = default;
+
+    // virtual so that test harness can override platform-specific behavior
+    virtual bool canRasterizeGlyph(const FontStack&, GlyphID);
+    virtual Glyph rasterizeGlyph(const FontStack&, GlyphID);
+};
+
+} // namespace mbgl