[core] Line-break ideographic text by character (#6828)

* [core] Line-break ideographic text by character

Allow a line break to be inserted after any supported Chinese, Japanese, or Yi character in a point-placed label. Balance the lines unless non-ideographic text such as Latin letters are present.

Fixes #1223.

* [core] Moved more character classing into util::i18n

* [core] Detect character properties by Unicode block

* [test] Reenabled ideographic breaking tests

1 files changed, 27 insertions, 0 deletions

diff --git a/src/mbgl/util/i18n.hpp b/src/mbgl/util/i18n.hpp
new file mode 100644
index 0000000000..fe324f5362
--- /dev/null
+++ b/src/mbgl/util/i18n.hpp
@@ -0,0 +1,27 @@
+#pragma once
+
+#include <string>
+
+namespace mbgl {
+namespace util {
+namespace i18n {
+
+/** Returns whether a character is a visible character. */
+bool isVisible(uint32_t chr);
+
+/** Returns whether a line break can be inserted after the character indicated
+    by the given Unicode codepoint due to word breaking. */
+bool allowsWordBreaking(uint32_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
+    instead. */
+bool allowsIdeographicBreaking(const std::u32string& string);
+
+/** Returns whether a line break can be inserted after the character indicated
+    by the given Unicode codepoint due to ideographic breaking. */
+bool allowsIdeographicBreaking(uint32_t chr);
+
+} // namespace i18n
+} // namespace util
+} // namespace mbgl