Add ncegc_len function to API

include/notcurses/notcurses.h

@@ -593,6 +593,17 @@ ncchannels_set_bg_default(uint64_t* channels){
 // 0x0--0x10ffff can be UTF-8-encoded with only 4 bytes
 #define WCHAR_MAX_UTF8BYTES 4
 
+// Calculate the length and width of the next EGC in the UTF-8 string input.
+// We use libunistring's uc_is_grapheme_break() to segment EGCs. Writes the
+// number of columns to '*colcount'. Returns the number of bytes consumed,
+// not including any NUL terminator. Neither the number of bytes nor columns
+// is necessarily equal to the number of decoded code points. Such are the
+// ways of Unicode. uc_is_grapheme_break() wants UTF-32, which is fine, because
+// we need wchar_t to use wcwidth() anyway FIXME except this doesn't work with
+// 16-bit wchar_t!
+API int ncegc_len(const char* gcluster, int* colcount)
+  __attribute__ ((nonnull (1)));
+
 // Returns the number of columns occupied by the longest valid prefix of a
 // multibyte (UTF-8) string. If an invalid character is encountered, -1 will be
 // returned, and the number of valid bytes and columns will be written into

src/lib/notcurses.c

@@ -3269,6 +3269,10 @@ int ncplane_putwstr_stained(ncplane* n, const wchar_t* gclustarr){
   return r;
 }
 
+int ncegc_len(const char* gcluster, int* colcount){
+  return utf8_egc_len(gcluster, colcount);
+}
+
 int notcurses_ucs32_to_utf8(const uint32_t* ucs32, unsigned ucs32count,
                             unsigned char* resultbuf, size_t buflen){
   if(u32_to_u8(ucs32, ucs32count, resultbuf, &buflen) == NULL){