From f89300d4264069e50a42c7e26b428957e750b437 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sun, 16 Jun 2019 11:54:18 +0300
Subject: [PATCH] Add simple ligature support to Font

Currently only two-character ligatures are supported.
---
 source/font.cpp | 31 ++++++++++++++++++++++++++-----
 source/font.h   |  8 ++++++--
 2 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/source/font.cpp b/source/font.cpp
index 54631926..3fd24d8e 100644
--- a/source/font.cpp
+++ b/source/font.cpp
@@ -44,7 +44,7 @@ void Font::add_glyph(const Glyph &g)
 
 void Font::set_kerning(unsigned l, unsigned r, float d)
 {
-	kerning[KerningKey(l, r)] = d;
+	kerning[CodePair(l, r)] = d;
 }
 
 float Font::get_string_width(const string &str, StringCodec::Decoder &dec) const
@@ -77,9 +77,18 @@ void Font::build_string(const string &str, StringCodec::Decoder &dec, PrimitiveB
 	MatrixStack::Push push_mtx(bld.matrix());
 
 	unsigned prev = 0;
-	for(string::const_iterator i=str.begin(); i!=str.end();)
+	unsigned next = 0;
+	for(string::const_iterator i=str.begin(); (next || i!=str.end());)
 	{
-		unsigned c = dec.decode_char(str, i);
+		unsigned c = (next ? next : dec.decode_char(str, i));
+		next = (i!=str.end() ? dec.decode_char(str, i) : 0);
+
+		if(unsigned lig = get_ligature(c, next))
+		{
+			c = lig;
+			next = 0;
+		}
+
 		GlyphMap::const_iterator j = glyphs.find(c);
 		if(j==glyphs.end())
 			continue;
@@ -116,7 +125,7 @@ float Font::get_glyph_advance(unsigned code, unsigned next) const
 
 	if(next)
 	{
-		KerningMap::const_iterator j = kerning.find(KerningKey(code, next));
+		KerningMap::const_iterator j = kerning.find(CodePair(code, next));
 		if(j!=kerning.end())
 			advance += j->second;
 	}
@@ -124,6 +133,12 @@ float Font::get_glyph_advance(unsigned code, unsigned next) const
 	return advance;
 }
 
+unsigned Font::get_ligature(unsigned code, unsigned next) const
+{
+	LigatureMap::const_iterator i = ligatures.find(CodePair(code, next));
+	return (i!=ligatures.end() ? i->second : 0);
+}
+
 
 Font::Loader::Loader(Font &f):
 	DataFile::CollectionObjectLoader<Font>(f, 0)
@@ -147,6 +162,7 @@ void Font::Loader::init()
 	add("texture",     &Loader::texture_ref);
 	add("glyph",       &Loader::glyph);
 	add("kerning",     &Loader::kerning);
+	add("ligature",    &Loader::ligature);
 	add("x_height",    &Font::x_height);
 }
 
@@ -160,7 +176,12 @@ void Font::Loader::glyph(unsigned c)
 
 void Font::Loader::kerning(unsigned l, unsigned r, float d)
 {
-	obj.kerning[KerningKey(l, r)] = d;
+	obj.kerning[CodePair(l, r)] = d;
+}
+
+void Font::Loader::ligature(unsigned l, unsigned r, unsigned g)
+{
+	obj.ligatures[CodePair(l, r)] = g;
 }
 
 void Font::Loader::texture()
diff --git a/source/font.h b/source/font.h
index 4eaed963..dab09fa4 100644
--- a/source/font.h
+++ b/source/font.h
@@ -29,6 +29,7 @@ public:
 		void init();
 		void glyph(unsigned);
 		void kerning(unsigned, unsigned, float);
+		void ligature(unsigned, unsigned, unsigned);
 		void texture();
 		void texture_ref(const std::string &);
 	};
@@ -53,8 +54,9 @@ public:
 
 private:
 	typedef std::map<unsigned, Glyph> GlyphMap;
-	typedef std::pair<unsigned, unsigned> KerningKey;
-	typedef std::map<KerningKey, float> KerningMap;
+	typedef std::pair<unsigned, unsigned> CodePair;
+	typedef std::map<CodePair, float> KerningMap;
+	typedef std::map<CodePair, unsigned> LigatureMap;
 
 	RefPtr<const Texture2D> texture;
 	float native_size;
@@ -64,6 +66,7 @@ private:
 	float x_height;
 	GlyphMap glyphs;
 	KerningMap kerning;
+	LigatureMap ligatures;
 
 public:
 	Font();
@@ -133,6 +136,7 @@ public:
 private:
 	void create_glyph_quad(const Glyph &, PrimitiveBuilder &) const;
 	float get_glyph_advance(unsigned, unsigned = 0) const;
+	unsigned get_ligature(unsigned, unsigned) const;
 };
 
 } // namespace GL
-- 
2.43.0