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

[Charles A. Roelli]

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.

I notice now, though, that the tooltip can end up partially offscreen, 
both with and without the above change (e.g. when you create a tooltip 
with the mouse pointer at the right edge of the primary monitor).  IIRC 
on GNU/Linux the tooltip is adjusted to fit on screen.  Maybe this 
adjustment works on newer versions of OS X?