[v1] vt: implement proper Unicode handling

[PATCH 11/11] vt: pad double-width code points with a zero-white-space

Posted by Nicolas Pitre 8 months, 1 week ago

From: Nicolas Pitre <npitre@baylibre.com>

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 or selection.

Let's use a better code point for the column padding's purpose i.e. a
zero-white-space rather than a full space.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
---
 drivers/tty/vt/vt.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index e3d35c4f92..dc84f9c6b7 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -2937,12 +2937,13 @@ static int vc_con_write_normal(struct vc_data *vc, int tc, int c,
 			width = 2;
 		} else if (ucs_is_zero_width(c)) {
 			prev_c = vc_uniscr_getc(vc, -1);
-			if (prev_c == ' ' &&
+			if (prev_c == 0x200B &&
 			    ucs_is_double_width(vc_uniscr_getc(vc, -2))) {
 				/*
 				 * Let's merge this zero-width code point with
 				 * the preceding double-width code point by
-				 * replacing the existing whitespace padding.
+				 * replacing the existing zero-white-space
+				 * padding.
 				 */
 				vc_con_rewind(vc);
 			} else if (c == 0xfe0f && prev_c != 0) {
@@ -3040,7 +3041,11 @@ 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-white-space in the Unicode screen given that
+		 * the previous code point is semantically double-width.
+		 */
+		next_c = 0x200B;
 	}
 
 out:
-- 
2.49.0

Re: [PATCH 11/11] vt: pad double-width code points with a zero-white-space

Posted by Jiri Slaby 8 months, 1 week ago

On 10. 04. 25, 3:14, Nicolas Pitre wrote:
> From: Nicolas Pitre <npitre@baylibre.com>
> 
> 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 or selection.
> 
> Let's use a better code point for the column padding's purpose i.e. a
> zero-white-space rather than a full space.
> 
> Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
> ---
>   drivers/tty/vt/vt.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index e3d35c4f92..dc84f9c6b7 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -2937,12 +2937,13 @@ static int vc_con_write_normal(struct vc_data *vc, int tc, int c,
>   			width = 2;
>   		} else if (ucs_is_zero_width(c)) {
>   			prev_c = vc_uniscr_getc(vc, -1);
> -			if (prev_c == ' ' &&
> +			if (prev_c == 0x200B &&

Then introduce a NAME (macro) for this.

thanks,
-- 
js
suse labs