bug#26905: 25.2: MacOS: tooltips show in wrong display

["Charles A. Roelli" <charles@aurox.ch>]

FWIW, I found this change to the Windows port of Emacs (not sure if it 
was ever committed):


https://lists.gnu.org/archive/html/bug-gnu-emacs/2007-07/msg00153.html


And a more recent change as a result of #22549: commit 
c77ffc8019bceb850a794c13f2e3ad991cc7e412, with changes to xfns.c.


c77ffc8..: Oscar Fuentes 2016-02-06 Use monitor's resolution for 
positioning tooltips
   commit c77ffc8019bceb850a794c13f2e3ad991cc7e412
   Author: Oscar Fuentes <ofv@wanadoo.es>
   Date:   Sat Feb 6 22:12:53 2016 +0100

   Use monitor's resolution for positioning tooltips

   * src/xfns.c (compute_tip_xy): Use the resolution of the monitor where
   the mouse pointer is to avoid placing the tooltip over the border of
   the monitor on multi-head displays. Fixes bug#22549.


Seems like the Windows and X versions nowadays have a check that looks 
like this:

   else if (*root_x + XINT (dx) <= min_x)
     *root_x = 0; /* Can happen for negative dx */

i.e. compare *root_x + XINT (dx) against the variable "min_x", rather 
than comparing against zero, as is done in the NS port. Since frames can 
be in the negative coordinate space, it makes sense to allow a tooltip 
to have a x-coordinate less than 0 -- so the NS port's code should 
probably be changed.


I'm also not sure why, in the above code from the Windows and X 
versions, *root_x is constrained to zero if *root_x + dx goes below 
min_x.  Wouldn't it make more sense to constrain to min_x, which could 
be negative?


On 13/05/2017 11:56, Eli Zaretskii wrote:
>> From: "Charles A. Roelli" <charles@aurox.ch>
>> Date: Sat, 13 May 2017 11:02:04 +0200
>>
>> If I remove the marked lines in compute_tip_xy:
>>
>>       if (INTEGERP (left) || INTEGERP (right))
>>         *root_x = pt.x;
>> =>  else if (pt.x + XINT (dx) <= 0)
>> =>    *root_x = 0; /* Can happen for negative dx */
>>       else if (pt.x + XINT (dx) + width
>> 	     <= x_display_pixel_width (FRAME_DISPLAY_INFO (f)))
>>         /* It fits to the right of the pointer.  */
>>         *root_x = pt.x + XINT (dx);
>>       else if (width + XINT (dx) <= pt.x)
>>         /* It fits to the left of the pointer.  */
>>         *root_x = pt.x - width - XINT (dx);
>>       else
>>         /* Put it left justified on the screen -- it ought to fit that way.  */
>>         *root_x = 0;
>>
>> Then the problem is gone.
> Those lines were added to fix some problems (whose particulars I
> cannot find at the moment), so we shouldn't remove them without
> understanding what is going on.