[PATCH] lib/fonts: Fix bit position when rotating by 180 degrees

[PATCH] lib/fonts: Fix bit position when rotating by 180 degrees

[Thomas Zimmermann]

Fix the horizontal bit position when rotating a glyph by 180°. The
original code in rotate_ud() rounded the value in width up to a
multiple of 8, aka the bit pitch, and calculated the rotated pixel
from that value. The new code stores the glyph's pitch in bit_pitch,
but fails to update the rotated pixel's output accordingly. Simply
replacing the variable does this.

The bug can be reproduced by setting a font with an unaligned width,
such as sun12x22, like this:

 setfont sun12x22
 echo 2 > /sys/class/graphics/fbcon/rotate

Without the fix, the font looks distorted.

Fixes: a30e9e6b018f ("lib/fonts: Refactor glyph-rotation helpers")
Closes: https://lore.gitlab.freedesktop.org/drm-ai-reviews/review-patch7-20260407092555.58816-8-tzimmermann@suse.de/
Cc: dri-devel@lists.freedesktop.org
Cc: linux-fbdev@vger.kernel.org
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 lib/fonts/font_rotate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/fonts/font_rotate.c b/lib/fonts/font_rotate.c
index 065e0fc0667b..275406008823 100644
--- a/lib/fonts/font_rotate.c
+++ b/lib/fonts/font_rotate.c
@@ -106,7 +106,7 @@ static void __font_glyph_rotate_180(const unsigned char *glyph,
 	for (y = 0; y < height; y++) {
 		for (x = 0; x < width; x++) {
 			if (font_glyph_test_bit(glyph, x, y, bit_pitch)) {
-				font_glyph_set_bit(out, width - (1 + x + shift), height - (1 + y),
+				font_glyph_set_bit(out, bit_pitch - 1 - x - shift, height - 1 - y,
 						   bit_pitch);
 			}
 		}
-- 
2.54.0

Re: [PATCH] lib/fonts: Fix bit position when rotating by 180 degrees

[Helge Deller]

On 4/28/26 10:28, Thomas Zimmermann wrote:
> Fix the horizontal bit position when rotating a glyph by 180°. The
> original code in rotate_ud() rounded the value in width up to a
> multiple of 8, aka the bit pitch, and calculated the rotated pixel
> from that value. The new code stores the glyph's pitch in bit_pitch,
> but fails to update the rotated pixel's output accordingly. Simply
> replacing the variable does this.
> 
> The bug can be reproduced by setting a font with an unaligned width,
> such as sun12x22, like this:
> 
>   setfont sun12x22
>   echo 2 > /sys/class/graphics/fbcon/rotate
> 
> Without the fix, the font looks distorted.
> 
> Fixes: a30e9e6b018f ("lib/fonts: Refactor glyph-rotation helpers")
> Closes: https://lore.gitlab.freedesktop.org/drm-ai-reviews/review-patch7-20260407092555.58816-8-tzimmermann@suse.de/
> Cc: dri-devel@lists.freedesktop.org
> Cc: linux-fbdev@vger.kernel.org
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>   lib/fonts/font_rotate.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

applied.
Thanks!
Helge