[core] Add minimal line breaking support for RTL text.

4 files changed, 22 insertions, 12 deletions

diff --git a/src/mbgl/text/bidi.cpp b/src/mbgl/text/bidi.cpp
index 2b6967110c..4c127e9cab 100644
--- a/src/mbgl/text/bidi.cpp
+++ b/src/mbgl/text/bidi.cpp
@@ -2,6 +2,7 @@
 
 #include <mbgl/text/bidi.hpp>
 #include <unicode/ubidi.h>
+#include <unicode/ubiditransform.h>
 #include <unicode/ushape.h>
 
 namespace mbgl {
@@ -44,10 +45,12 @@ std::u16string BiDi::bidiTransform(const std::u16string& input) {
     return std::u16string(outputText.get(), outputLength);
 }
 
-bool BiDi::baseDirectionRightToLeft(const std::u16string& input) {
+WritingDirection BiDi::baseWritingDirection(const std::u16string& input) {
     // This just looks for the first character with a strong direction property, it does not perform
     // the BiDi algorithm
-    return ubidi_getBaseDirection(input.c_str(), static_cast<int32_t>(input.size())) == UBIDI_RTL;
+    return ubidi_getBaseDirection(input.c_str(), static_cast<int32_t>(input.size())) == UBIDI_RTL
+        ? WritingDirection::RightToLeft
+        : WritingDirection::LeftToRight;
 }
 
 } // end namespace mbgl
diff --git a/src/mbgl/text/bidi.hpp b/src/mbgl/text/bidi.hpp
index 030ac88ce2..e29bf041e2 100644
--- a/src/mbgl/text/bidi.hpp
+++ b/src/mbgl/text/bidi.hpp
@@ -3,17 +3,20 @@
 #include <string>
 
 #include <mbgl/util/noncopyable.hpp>
-#include <unicode/ubiditransform.h>
 
-namespace mbgl {
+struct UBiDiTransform;
 
+namespace mbgl {
+    
+enum class WritingDirection : bool { LeftToRight, RightToLeft };    
+    
 class BiDi : private util::noncopyable {
 public:
     BiDi();
     ~BiDi();
 
     std::u16string bidiTransform(const std::u16string&);
-    bool baseDirectionRightToLeft(const std::u16string&);
+    WritingDirection baseWritingDirection(const std::u16string&);
 
 private:
     UBiDiTransform* transform;
diff --git a/src/mbgl/text/glyph_set.cpp b/src/mbgl/text/glyph_set.cpp
index f0e3991540..67c2ab93e4 100644
--- a/src/mbgl/text/glyph_set.cpp
+++ b/src/mbgl/text/glyph_set.cpp
@@ -2,6 +2,7 @@
 #include <mbgl/platform/log.hpp>
 #include <mbgl/math/minmax.hpp>
 #include <mbgl/util/i18n.hpp>
+#include <mbgl/text/bidi.hpp>
 
 #include <cassert>
 
@@ -31,7 +32,7 @@ const std::map<uint32_t, SDFGlyph> &GlyphSet::getSDFs() const {
     return sdfs;
 }
 
-const Shaping GlyphSet::getShaping(const std::u16string &string, const float maxWidth,
+const Shaping GlyphSet::getShaping(const std::u16string &string, const WritingDirection writingDirection, const float maxWidth,
                                     const float lineHeight, const float horizontalAlign,
                                     const float verticalAlign, const float justify,
                                     const float spacing, const Point<float> &translate) const {
@@ -56,7 +57,7 @@ const Shaping GlyphSet::getShaping(const std::u16string &string, const float max
         return shaping;
 
     lineWrap(shaping, lineHeight, maxWidth, horizontalAlign, verticalAlign, justify, translate,
-             util::i18n::allowsIdeographicBreaking(string));
+             util::i18n::allowsIdeographicBreaking(string), writingDirection);
 
     return shaping;
 }
@@ -90,7 +91,9 @@ void justifyLine(std::vector<PositionedGlyph> &positionedGlyphs, const std::map<
 void GlyphSet::lineWrap(Shaping &shaping, const float lineHeight, float maxWidth,
                         const float horizontalAlign, const float verticalAlign,
                         const float justify, const Point<float> &translate,
-                        bool useBalancedIdeographicBreaking) const {
+                        bool useBalancedIdeographicBreaking, const WritingDirection writingDirection) const {
+    float lineFeedOffset = writingDirection == WritingDirection::RightToLeft ? -lineHeight : lineHeight;
+    
     uint32_t lastSafeBreak = 0;
 
     uint32_t lengthBeforeCurrentLine = 0;
@@ -112,7 +115,7 @@ void GlyphSet::lineWrap(Shaping &shaping, const float lineHeight, float maxWidth
             PositionedGlyph &shape = positionedGlyphs[i];
 
             shape.x -= lengthBeforeCurrentLine;
-            shape.y += lineHeight * line;
+            shape.y += lineFeedOffset * line;
 
             if (shape.x > maxWidth && lastSafeBreak > 0) {
 
@@ -120,7 +123,7 @@ void GlyphSet::lineWrap(Shaping &shaping, const float lineHeight, float maxWidth
                 maxLineLength = util::max(lineLength, maxLineLength);
 
                 for (uint32_t k = lastSafeBreak + 1; k <= i; k++) {
-                    positionedGlyphs[k].y += lineHeight;
+                    positionedGlyphs[k].y += lineFeedOffset;
                     positionedGlyphs[k].x -= lineLength;
                 }
 
diff --git a/src/mbgl/text/glyph_set.hpp b/src/mbgl/text/glyph_set.hpp
index 004cae343d..b4fcf4c3a4 100644
--- a/src/mbgl/text/glyph_set.hpp
+++ b/src/mbgl/text/glyph_set.hpp
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <mbgl/text/bidi.hpp>
 #include <mbgl/text/glyph.hpp>
 #include <mbgl/util/geometry.hpp>
 
@@ -9,12 +10,12 @@ class GlyphSet {
 public:
     void insert(uint32_t id, SDFGlyph&&);
     const std::map<uint32_t, SDFGlyph> &getSDFs() const;
-    const Shaping getShaping(const std::u16string &string, float maxWidth, float lineHeight,
+    const Shaping getShaping(const std::u16string &string, const WritingDirection writingDirection, float maxWidth, float lineHeight,
                              float horizontalAlign, float verticalAlign, float justify,
                              float spacing, const Point<float> &translate) const;
     void lineWrap(Shaping &shaping, float lineHeight, float maxWidth, float horizontalAlign,
                   float verticalAlign, float justify, const Point<float> &translate,
-                  bool useBalancedIdeographicBreaking) const;
+                  bool useBalancedIdeographicBreaking, const WritingDirection writingDirection) const;
 
 private:
     std::map<uint32_t, SDFGlyph> sdfs;