bug#16856: 24.3.50; Cursor leaves garbage in fringe

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 17 Jul 2016 09:42:32 +0100
> From: Alan Third <alan@idiocy.org>
> Cc: 16856@debbugs.gnu.org
> 
> On Sun, Jul 17, 2016 at 03:33:03PM +0900, David Reitter wrote:
> > I don’t think that bea0f95 (May 21, nsterm.m) fully fixed this
> > problem. I’ve had several “appearances” of the ominous garbage in
> > the right fringe yesterday.
> > 
> > This was after applying your patch (and removing my workaround).
> 
> Hi David, I'm not entirely sure what's going on in your screenshot. Is
> the garbage definitely appearing in the fringe rather than in the main
> text area? If so, is it on the left or the right (or the middle, I
> guess) of the fringe?

I actually am puzzled by more than that: it looks like the "garbage"
is some text drawn on the fringe, which seems to point to incorrect
coordinates of some screen write.  If that screen write is the one
that draws or erases the cursor, then I don't understand this comment:

  "Because the cursor is drawn without limiting focus to the window
   box, but it is removed by writing glyph and nothing into the right
   margin, while focus is applied to the window box, parts of the
   cursor may remain visible."

It seems to imply that drawing cursor and erasing it are implemented
in Aquamacs by two very different code fragments?  (That's not what
happens on other platforms, AFAIR.)  And if that's true, I understand
the workaround even less: it limits the _width_ of the cursor, whereas
the problem is clearly with its coordinates.

What am I missing?