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vt: pad double-width code points with a zero-width space

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In the Unicode screen buffer, we follow double-width code points with a
space to maintain proper column alignment. This, however, creates
semantic problems when e.g. using cut and paste.

Let's use a better code point for the column padding's purpose i.e. a
zero-width space rather than a full space. This way the combination
retains a width of 2.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20250417184849.475581-11-nico@fluxnic.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Nicolas Pitre 2025-04-17 14:45:12 -04:00 committed by Greg Kroah-Hartman
parent b5c574995d
commit 5617aeb14a
1 changed files with 8 additions and 3 deletions
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11
drivers/tty/vt/vt.c
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@ -2923,6 +2923,7 @@ static void vc_con_rewind(struct vc_data *vc)
vc->vc_need_wrap = 0;
}
#define UCS_ZWS 0x200b /* Zero Width Space */
#define UCS_VS16 0xfe0f /* Variation Selector 16 */
static int vc_process_ucs(struct vc_data *vc, int *c, int *tc)
@ -2941,8 +2942,8 @@ static int vc_process_ucs(struct vc_data *vc, int *c, int *tc)
/*
* Let's merge this zero-width code point with the preceding
* double-width code point by replacing the existing
* whitespace padding. To do so we rewind one column and
* pretend this has a width of 1.
* zero-width space padding. To do so we rewind one column
* and pretend this has a width of 1.
* We give the legacy display the same initial space padding.
*/
vc_con_rewind(vc);
@ -3065,7 +3066,11 @@ static int vc_con_write_normal(struct vc_data *vc, int tc, int c,
tc = conv_uni_to_pc(vc, ' ');
if (tc < 0)
tc = ' ';
next_c = ' ';
/*
* Store a zero-width space in the Unicode screen given that
* the previous code point is semantically double width.
*/
next_c = UCS_ZWS;
}
out: