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, 5 insertions, 4 deletions

diff --git a/src/nvim/mouse.c b/src/nvim/mouse.c
index 6f636f643a..96d20b6a32 100644
--- a/src/nvim/mouse.c
+++ b/src/nvim/mouse.c
@@ -108,12 +108,13 @@ retnomove:
     goto retnomove;                             // ugly goto...
 
   // Remember the character under the mouse, it might be a '-' or '+' in the
-  // fold column.
+  // fold column. NB: only works for ASCII chars!
   if (row >= 0 && row < Rows && col >= 0 && col <= Columns
-      && ScreenLines != NULL)
-    mouse_char = ScreenLines[LineOffset[row] + (unsigned)col];
-  else
+      && ScreenLines != NULL) {
+    mouse_char = ScreenLines[LineOffset[row] + (unsigned)col][0];
+  } else {
     mouse_char = ' ';
+  }
 
   old_curwin = curwin;
   old_cursor = curwin->w_cursor;