commit 9f51eb99fd04cf87cbb83fe5ef594abd3153b892
parent 51d36756c20692a7fddb8acfa37cf965d8e22921
Author: Claudio Alessi <smoppy@gmail.com>
Date: Sun, 11 Jan 2026 22:27:02 +0100
Use ZWNJ for RIS to ensure consistent drawing.
Modern terminals don't rely on wcwidth(). Rather they uses an internal
render logic through engine like HarfBuzz or the like. This means that
individual parts of a RIS emoji (e.g. I and T of italian flag) are
1-column wide on st but 2-columns wide on kitty. Furthermore we see
individual I and T on st but an actual flag in kitty.
To ensure we always sees the same thing regardless on the terminal a
Zero-Width Non-Joiner gets inserted between individual components of
Regional Indicator Symbols. This way we have predictable drawings in
compatibility mode which is currently the default.
Diffstat:
| M | tui.c | | | 21 | +++++++++++++++------ |
1 file changed, 15 insertions(+), 6 deletions(-)
diff --git a/tui.c b/tui.c
@@ -21,6 +21,7 @@
#define CURHIDE "\33[?25l"
#define CURSHOW "\33[?25h"
#define ERASECHAR "\33[1X"
+#define ZWNJ "\xe2\x80\x8c"
/* UTF-8 Regional Indicator Symbol */
#define IS_RIS(c) ((c) >= 0x1F1E6 && (c) <= 0x1F1FF)
@@ -191,7 +192,7 @@ tui_move_cursor(int c, int r) {
void
tui_draw_line_compat(UI *ui, int x, int y, Cell *cells, int count) {
char *txt;
- int neederase, i;
+ int i;
tui_move_cursor(x, y);
for(i = 0; i < count; i++) {
@@ -200,13 +201,10 @@ tui_draw_line_compat(UI *ui, int x, int y, Cell *cells, int count) {
unsigned int cp;
int o = 0;
- neederase = 0;
while(o < cells[i].len) {
int step = utf8_decode(txt + o, cells[i].len - o, &cp);
int cw = cells[i].width;
-
- if(cells[i].len > 1 && (cells[i].width == 1 || IS_RIS(cp)))
- neederase = 1;
+ int neederase = cells[i].len > 1 && (cells[i].width == 1 || IS_RIS(cp));
switch(cp) {
case 0x200D:
@@ -220,13 +218,24 @@ tui_draw_line_compat(UI *ui, int x, int y, Cell *cells, int count) {
default:
/* don't expect negative values here */
cw = wcwidth(cp);
- assert(cw >= 0);
+ if(cw < 0) cw = 0;
if(neederase) {
const char t[] = "\x1b[48;5;232m"ERASECHAR;
ab_write(&frame, t, sizeof t - 1);
}
+
ab_write(&frame, txt + o, step);
+
+ /* to preserve coherence between terminals always split RIS
+ * so that we can see individual components. This is needed
+ * to ensure cursor synchronization between terminals that
+ * renders the same glyph with 2 different widths. */
+ if(IS_RIS(cp)) {
+ const char t[] = ZWNJ;
+ ab_write(&frame, t, sizeof t - 1);
+ }
+
if(neederase) {
const char t[] = "\x1b[0m";
ab_write(&frame, t, sizeof t - 1);
