[core] Use UTF-16 instead of UTF-32 for label features to avoid extra conversions and reduce in-memory size.

Continue to use uint32 as glyph ID to maintain Glyph PBF, even though we're only using 16 bits of that uint32.
Use std::codecvt instead of boost::unicode_iterator for UTF8->UTF16 conversions.

4 files changed, 8 insertions, 8 deletions

diff --git a/src/mbgl/layout/merge_lines.cpp b/src/mbgl/layout/merge_lines.cpp
index f4fdb82617..676cbc092d 100644
--- a/src/mbgl/layout/merge_lines.cpp
+++ b/src/mbgl/layout/merge_lines.cpp
@@ -47,10 +47,10 @@ enum class Side {
 };
 
 size_t
-getKey(const std::u32string& text, const GeometryCollection& geom, Side side) {
+getKey(const std::u16string& text, const GeometryCollection& geom, Side side) {
     const GeometryCoordinate& coord = side == Side::Right ? geom[0].back() : geom[0].front();
 
-    auto hash = std::hash<std::u32string>()(text);
+    auto hash = std::hash<std::u16string>()(text);
     boost::hash_combine(hash, coord.x);
     boost::hash_combine(hash, coord.y);
     return hash;
diff --git a/src/mbgl/layout/symbol_feature.hpp b/src/mbgl/layout/symbol_feature.hpp
index 99db4f9ac5..9e0eacaac5 100644
--- a/src/mbgl/layout/symbol_feature.hpp
+++ b/src/mbgl/layout/symbol_feature.hpp
@@ -10,7 +10,7 @@ namespace mbgl {
 class SymbolFeature {
 public:
     GeometryCollection geometry;
-    optional<std::u32string> text;
+    optional<std::u16string> text;
     optional<std::string> icon;
     std::size_t index;
 };
diff --git a/src/mbgl/layout/symbol_layout.cpp b/src/mbgl/layout/symbol_layout.cpp
index d974e6a357..7f8e8d5f83 100644
--- a/src/mbgl/layout/symbol_layout.cpp
+++ b/src/mbgl/layout/symbol_layout.cpp
@@ -90,10 +90,10 @@ SymbolLayout::SymbolLayout(std::string bucketName_,
                 u8string = platform::lowercase(u8string);
             }
 
-            ft.text = util::utf8_to_utf32::convert(u8string);
+            ft.text = util::utf8_to_utf16::convert( u8string );
 
             // Loop through all characters of this text and collect unique codepoints.
-            for (char32_t chr : *ft.text) {
+            for (char16_t chr : *ft.text) {
                 ranges.insert(getGlyphRange(chr));
             }
         }
@@ -309,7 +309,7 @@ void SymbolLayout::addFeature(const GeometryCollection &lines,
     }
 }
 
-bool SymbolLayout::anchorIsTooClose(const std::u32string &text, const float repeatDistance, Anchor &anchor) {
+bool SymbolLayout::anchorIsTooClose(const std::u16string &text, const float repeatDistance, Anchor &anchor) {
     if (compareText.find(text) == compareText.end()) {
         compareText.emplace(text, Anchors());
     } else {
diff --git a/src/mbgl/layout/symbol_layout.hpp b/src/mbgl/layout/symbol_layout.hpp
index 54acf84aaf..9a580900dd 100644
--- a/src/mbgl/layout/symbol_layout.hpp
+++ b/src/mbgl/layout/symbol_layout.hpp
@@ -64,8 +64,8 @@ private:
                     const GlyphPositions& face,
                     const size_t index);
 
-    bool anchorIsTooClose(const std::u32string& text, const float repeatDistance, Anchor&);
-    std::map<std::u32string, std::vector<Anchor>> compareText;
+    bool anchorIsTooClose(const std::u16string& text, const float repeatDistance, Anchor&);
+    std::map<std::u16string, std::vector<Anchor>> compareText;
 
     void addToDebugBuffers(CollisionTile&, SymbolBucket&);