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

[Eli Zaretskii <eliz@gnu.org>]

> From: "Drew Adams" <drew.adams@oracle.com>
> Cc: <handa@gnu.org>, <mario.giovinazzo@virgilio.it>, <13011@debbugs.gnu.org>
> Date: Mon, 3 Dec 2012 10:41:52 -0800
> 
> Apart from that example, I imagine that this also affects any text that uses a
> face that has a box with a negative :line-width.  Is that correct?

Yes.

> If so, that will impact faces that I use.  And IIUC, it means that the text
> displayed in the boxed face will have its first and last chars partly obscured
> by the box border.  Is that right?

Right.

> I guess I would not object to making such a change for situations where the
> chars to be partly obscured are whitespace only.  But I do object to overwriting
> typical chars such as those with word or symbol syntax.

How about doing that only for 1-pixel borders?

> Attached is a screenshot from emacs -Q.  IIUC, you are saying that instead of
> the text shown in mode-line-highlight face being slightly misaligned wrt the
> other text, so that the `a' is not partly obscured by the left box border, the
> text would be aligned with the others and the boxed `a' would be partly obscured
> by the left box border.

Yes, that's it.

> Is the proposed change only a "fix" for negative values or does it
> affect also positive values?

Only negative values will be affected.

> What is the motivation for this change?

See the beginning of this bug report: when a box face is used for
hl-line mode, moving cursor vertically produces an annoying shift of
the lines as the cursor moves through them.

> Would it be possible for this to be a user choice?

It's possible.