bug#6609: 23.2; Cursor becomes invisible when put over some faces

[Eli Zaretskii <eliz@gnu.org>]

> From: Deniz Dogan <deniz.a.m.dogan@gmail.com>
> Date: Sun, 11 Jul 2010 19:24:48 +0200
> Cc: 6609@debbugs.gnu.org
> 
> 2010/7/11 Eli Zaretskii <eliz@gnu.org>:
> >> From: Deniz Dogan <deniz.a.m.dogan@gmail.com>
> >> Date: Sun, 11 Jul 2010 19:02:21 +0200
> >> Cc: 6609@debbugs.gnu.org
> >>
> >> >> What happens if you evaluate this:
> >> >>
> >> >>  (set-face-background 'cursor "black")
> >> >>
> >> >
> >> > It returns nil and doesn't seem to have any effect on the problem I'm having.
> >> >
> >>
> >> Actually, it seems to make the cursor black, "covering" text with the
> >> default face. So now I can sort of guess where the cursor is by
> >> looking for gaps in the text, but it's of course still not
> >> satisfactory.
> >
> > And if you use a color other than black? does the above has the
> > expected effect?
> >
> > IOW, is the problem only with the black color, or with any color, as
> > far as the `cursor' face is concerned?
> >
> 
> Setting it to white or red or yellow gives me the desired effect. Thanks.
> 
> But this still should not be needed, so I'd like it if you don't close this bug.

Who said anything about closing?  I'm just warming up.

So let's back up a bit and see if we have the whole picture:

 . What happens in "emacs -Q" without evaluating

     (set-foreground-color "black")
     (set-background-color "white")

   ?  Is the cursor visible?  Is it black?

 . Which one of the above expressions triggers the problem when
   evaluated?  Is the order of evaluating them important?

 . When you set the background color of the `cursor' face, does the
   problem happen only with the black color?  What about colors close
   to black, like "gray1", "gray2", etc.? how about "gray40" or
   "gray80"?