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

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

>> (custom-set-variables '(global-hl-line-mode t))
>> (custom-set-faces '(hl-line ((t (:box (:line-width 1 :color "gray50"))))))
> Thanks.

Actually the interesting case is when the box is of width -1.

> I see no flickering when moving cursor horizontally within the same
> screen line.  None at all.

The problem is when moving vertically.

> If the above is what you see, then please tell what you expect Emacs
> to do instead.

When the box width is 1, indeed, there's no much Emacs could do, but
when the width is -1 (i.e. drawn "inside" the normal text box),
characters shouldn't move, whereas they do (they get shifted
horizontally by a few pixels, and if you try it in the *Help* buffer
you may see that the number of pixel shifts seems to increase at
transition points between different fonts, such as italics for function
arguments).


        Stefan