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Fix grapheme cluster width #126

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Merged
adsr merged 1 commit into from
Jan 2, 2026
Merged

Fix grapheme cluster width #126

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54 changes: 31 additions & 23 deletions termbox2.h
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Original file line number Diff line number Diff line change
Expand Up @@ -406,18 +406,18 @@ typedef uint16_t uintattr_t;
* `nech`, and `cech` via `tb_set_cell_ex`. `ech` is only valid when `nech>0`,
* otherwise `ch` is used.
*
* For non-single-width codepoints, given `N=wcwidth(ch)/wcswidth(ech)`:
* For non-single-width codepoints, given `W=wcwidth(ch || ech)`:
*
* when `N==0`: termbox forces a single-width cell. Callers should avoid this
* when `W<=0`: termbox forces a single-width cell. Callers should avoid this
* if aiming to render text accurately. Callers may use
* `tb_set_cell_ex` or `tb_print*` to render `N==0` combining
* `tb_set_cell_ex` or `tb_print*` to render `W==0` combining
* characters.
*
* when `N>1`: termbox zeroes out the following `N-1` cells and skips sending
* them to the tty. So, e.g., if the caller sets `x=0,y=0` to an
* `N==2` codepoint, the caller's next set should be at `x=2,y=0`.
* when `W>=2`: termbox zeroes out the following `W-1` cells and skips sending
* them to the tty. So, e.g., if the caller sets `x=0,y=0` to a
* `W==2` codepoint, the caller's next set should be at `x=2,y=0`.
* Anything set at `x=1,y=0` will be ignored. If there are not
* enough columns remaining on the line to render `N` width, spaces
* enough columns remaining on the line to render `W` cells, spaces
* are sent instead.
*
* See `tb_present` for implementation.
Expand Down Expand Up @@ -2329,7 +2329,7 @@ static int bytebuf_flush(struct bytebuf *b, int fd);
static int bytebuf_reserve(struct bytebuf *b, size_t sz);
static int bytebuf_free(struct bytebuf *b);
static int tb_iswprint_ex(uint32_t ch, int *width);
static int tb_wcswidth(uint32_t *ch, size_t nch);
static int tb_cluster_width(uint32_t *ch, size_t nch);

int tb_init(void) {
return tb_init_file("/dev/tty");
Expand Down Expand Up @@ -2424,12 +2424,12 @@ int tb_present(void) {
{
#ifdef TB_OPT_EGC
if (back->nech > 0)
w = tb_wcswidth(back->ech, back->nech);
w = tb_cluster_width(back->ech, back->nech);
else
#endif
w = tb_wcwidth((wchar_t)back->ch);
}
if (w < 1) w = 1; // wcwidth qreturns -1 for invalid codepoints
if (w < 1) w = 1; // wcwidth returns -1 for invalid codepoints

if (cell_cmp(back, front) != 0) {
cell_copy(front, back);
Expand Down Expand Up @@ -4237,27 +4237,35 @@ int tb_iswprint(uint32_t ch) {
}

int tb_wcwidth(uint32_t ch) {
int w;
#ifdef TB_OPT_LIBC_WCHAR
return wcwidth((wchar_t)ch);
w = wcwidth((wchar_t)ch);
#else
return tb_wcswidth(&ch, 1);
tb_iswprint_ex(ch, &w);
#endif
return w;
}

static int tb_wcswidth(uint32_t *ch, size_t nch) {
#ifdef TB_OPT_LIBC_WCHAR
return wcswidth((wchar_t *)ch, nch);
#else
int sw = 0;
static int tb_cluster_width(uint32_t *ch, size_t nch) {
int wmax = -1;
int vs15 = 0, vs16 = 0, ri = 0, zwj = 0;
size_t i = 0;
for (i = 0; i < nch; i++) {
int w;
tb_iswprint_ex(ch[i], &w);
if (w < 0) return -1;
sw += w;
uint32_t c = ch[i];
switch (c) {
case 0xfe0e: ++vs15; break;
case 0xfe0f: ++vs16; break;
case 0x200d: ++zwj; break;
default: if (c >= 0x1f1e6 && c <= 0x1f1ff) ++ri;
}
int w = tb_wcwidth(c);
if (w > wmax) wmax = w;
}
return sw;
#endif
if (wmax >= 1) {
if (vs15) return 1;
else if (vs16 || zwj || ri >= 2) return 2;
}
return wmax;
}

static int tb_iswprint_ex(uint32_t ch, int *w) {
Expand Down