screen: use UTF-8 representation

Store text in ScreenLines as UTF-8, so it can be sent as-is to the UI
layer. `utfc_char2bytes(off,buf)` is removed, as `ScreenLines[off]` now
already contains this representation.

To recover the codepoints that the screen arrays previously contained, use
utfc_ptr2char (or utf_ptr2char to ignore composing chars).

NB: This commit does NOT change how screen.c processes incoming UTF-8 data
from buffers, cmdline, messages etc. Any algorithm that operates on UCS-4
(like arabic shaping, treatment of non-printable chars)
is left unchanged for now.

1 files changed, 2 insertions, 23 deletions

diff --git a/src/nvim/mbyte.c b/src/nvim/mbyte.c
index 05e326104b..472c1ee9f6 100644
--- a/src/nvim/mbyte.c
+++ b/src/nvim/mbyte.c
@@ -560,7 +560,7 @@ size_t mb_string2cells(const char_u *str)
 /// We make sure that the offset used is less than "max_off".
 int utf_off2cells(unsigned off, unsigned max_off)
 {
-  return (off + 1 < max_off && ScreenLines[off + 1] == 0) ? 2 : 1;
+  return (off + 1 < max_off && ScreenLines[off + 1][0] == 0) ? 2 : 1;
 }
 
 /// Convert a UTF-8 byte sequence to a wide character
@@ -790,27 +790,6 @@ int utfc_ptr2char_len(const char_u *p, int *pcc, int maxlen)
 #undef ISCOMPOSING
 }
 
-/*
- * Convert the character at screen position "off" to a sequence of bytes.
- * Includes the composing characters.
- * "buf" must at least have the length MB_MAXBYTES + 1.
- * Only to be used when ScreenLinesUC[off] != 0.
- * Returns the produced number of bytes.
- */
-int utfc_char2bytes(int off, char_u *buf)
-{
-  int len;
-  int i;
-
-  len = utf_char2bytes(ScreenLinesUC[off], buf);
-  for (i = 0; i < Screen_mco; ++i) {
-    if (ScreenLinesC[i][off] == 0)
-      break;
-    len += utf_char2bytes(ScreenLinesC[i][off], buf + len);
-  }
-  return len;
-}
-
 /// Get the length of a UTF-8 byte sequence representing a single codepoint
 ///
 /// @param[in]  p  UTF-8 string.
@@ -1853,7 +1832,7 @@ int mb_fix_col(int col, int row)
   col = check_col(col);
   row = check_row(row);
   if (ScreenLines != NULL && col > 0
-      && ScreenLines[LineOffset[row] + col] == 0) {
+      && ScreenLines[LineOffset[row] + col][0] == 0) {
     return col - 1;
   }
   return col;