Upright CJK characters in vertically-oriented labels (#7114)

CJK characters and adjacent punctuation now remain upright in vertically oriented labels that have line placement.

Fixes #1682.

1 files changed, 48 insertions, 2 deletions

diff --git a/src/mbgl/util/i18n.hpp b/src/mbgl/util/i18n.hpp
index f1d3f53f72..186212f50d 100644
--- a/src/mbgl/util/i18n.hpp
+++ b/src/mbgl/util/i18n.hpp
@@ -8,7 +8,7 @@ namespace i18n {
 
 /** Returns whether a line break can be inserted after the character indicated
     by the given Unicode codepoint due to word breaking. */
-bool allowsWordBreaking(uint16_t chr);
+bool allowsWordBreaking(char16_t chr);
 
 /** Returns whether a line break can be inserted after any character in the
     given string. If false, line breaking should occur on word boundaries
@@ -17,7 +17,53 @@ bool allowsIdeographicBreaking(const std::u16string& string);
 
 /** Returns whether a line break can be inserted after the character indicated
     by the given Unicode codepoint due to ideographic breaking. */
-bool allowsIdeographicBreaking(uint16_t chr);
+bool allowsIdeographicBreaking(char16_t chr);
+
+/** Returns whether any substring of the given string can be drawn as vertical
+    text with upright glyphs. */
+bool allowsVerticalWritingMode(const std::u16string& string);
+
+/** Returns true if the given Unicode codepoint identifies a character with
+    upright orientation.
+
+    A character has upright orientation if it is drawn upright (unrotated)
+    whether the line is oriented horizontally or vertically, even if both
+    adjacent characters can be rotated. For example, a Chinese character is
+    always drawn upright. An uprightly oriented character causes an adjacent
+    “neutral” character to be drawn upright as well. */
+bool hasUprightVerticalOrientation(char16_t chr);
+
+/** Returns true if the given Unicode codepoint identifies a character with
+    neutral orientation.
+
+    A character has neutral orientation if it may be drawn rotated or unrotated
+    when the line is oriented vertically, depending on the orientation of the
+    adjacent characters. For example, along a verticlly oriented line, the
+    vulgar fraction ½ is drawn upright among Chinese characters but rotated
+    among Latin letters. A neutrally oriented character does not influence
+    whether an adjacent character is drawn upright or rotated.
+ */
+bool hasNeutralVerticalOrientation(char16_t chr);
+
+/** Returns true if the given Unicode codepoint identifies a character with
+    rotated orientation.
+
+    A character has rotated orientation if it is drawn rotated when the line is
+    oriented vertically, even if both adjacent characters are upright. For
+    example, a Latin letter is drawn rotated along a vertical line. A rotated
+    character causes an adjacent “neutral” character to be drawn rotated as
+    well.
+ */
+bool hasRotatedVerticalOrientation(char16_t chr);
+
+/** Returns a copy of the given string with punctuation characters replaced with
+    their vertical forms wherever applicable. */
+std::u16string verticalizePunctuation(const std::u16string& input);
+
+/** Returns the form of the given character appropriate for vertical text.
+
+    @return The character’s specialized vertical form; 0 if not applicable. */
+char16_t verticalizePunctuation(char16_t chr);
 
 } // namespace i18n
 } // namespace util