[core] Render half-width glyphs in upright orientation

This change forces glyphs whose natural orientation in vertical writing
mode is 'sideways' to be rendered in upright orientation (only for non complex
text layouts). This is different compared to W3C / browser behavior that is by
default, renders glyphs in their respective natural orientation.

In the future, there  might need to add a new layout property that would control
glyph orientation separately (e.g., text-glyph-orientation: natural | upright).

1 files changed, 12 insertions, 5 deletions

diff --git a/src/mbgl/text/shaping.cpp b/src/mbgl/text/shaping.cpp
index 3ed35fc725..7bf0e14f80 100644
--- a/src/mbgl/text/shaping.cpp
+++ b/src/mbgl/text/shaping.cpp
@@ -290,7 +290,8 @@ void shapeLines(Shaping& shaping,
                 const style::SymbolAnchorType textAnchor,
                 const style::TextJustifyType textJustify,
                 const WritingModeType writingMode,
-                const GlyphMap& glyphMap) {
+                const GlyphMap& glyphMap,
+                bool allowVerticalPlacement) {
     float x = 0;
     float y = Shaping::yOffset;
     
@@ -332,8 +333,13 @@ void shapeLines(Shaping& shaping,
             const double baselineOffset = (lineMaxScale - section.scale) * util::ONE_EM;
             
             const Glyph& glyph = **it->second;
-            
-            if (writingMode == WritingModeType::Horizontal || !util::i18n::hasUprightVerticalOrientation(codePoint)) {
+
+            if (writingMode == WritingModeType::Horizontal ||
+                // Don't verticalize glyphs that have no upright orientation if vertical placement is disabled.
+                (!allowVerticalPlacement && !util::i18n::hasUprightVerticalOrientation(codePoint)) ||
+                // If vertical placement is ebabled, don't verticalize glyphs that
+                // are from complex text layout script, or whitespaces.
+                (allowVerticalPlacement && (util::i18n::isWhitespace(codePoint) || util::i18n::isCharInComplexShapingScript(codePoint)))) {
                 shaping.positionedGlyphs.emplace_back(codePoint, x, y + baselineOffset, false, section.fontStackHash, section.scale, sectionIndex);
                 x += glyph.metrics.advance * section.scale + spacing;
             } else {
@@ -377,7 +383,8 @@ const Shaping getShaping(const TaggedString& formattedString,
                          const Point<float>& translate,
                          const WritingModeType writingMode,
                          BiDi& bidi,
-                         const GlyphMap& glyphs) {   
+                         const GlyphMap& glyphs,
+                         bool allowVerticalPlacement) {
     std::vector<TaggedString> reorderedLines;
     if (formattedString.sectionCount() == 1) {
         auto untaggedLines = bidi.processText(formattedString.rawText(),
@@ -394,7 +401,7 @@ const Shaping getShaping(const TaggedString& formattedString,
     }
     Shaping shaping(translate.x, translate.y, writingMode, reorderedLines.size());
     shapeLines(shaping, reorderedLines, spacing, lineHeight, textAnchor,
-               textJustify, writingMode, glyphs);
+               textJustify, writingMode, glyphs, allowVerticalPlacement);
     
     return shaping;
 }