bug#13011: 24.2; Text flickering moving cursor with box around text enabled

[Stefan Monnier <monnier@iro.umontreal.ca>]

>      area.  The vertical (left and right) borders of the box are drawn
>      in the same way as when this value is positive.  */
>   int box_line_width;
[...]
> I made a provisional change that behaves with left and right borders
> like it does with horizontal ones, and it seems to work, at least with
> character display (didn't text with images, image slices, composite
> characters, etc.).  But I'd like to ask Handa-san (CC'ed), who wrote
> the code for this feature (almost 12 years ago!), whether he might
> remember why the code deliberately makes the left and right borders
> behave differently from top and bottom ones.

I'm curious as well.  The only think that comes to mind is that in most
fonts, there's usually some empty pixel-line(s) at the top and the
bottom, whereas there often't isn't any empty pixel-lines at all on the
left (and/or on the right) side.  So there's more risk of overwriting
useful pixels on the left&right than at top&bottom.


        Stefan