bug#22549: 25.0.50; Tooltips placed outside of screen limits

[martin rudalics <rudalics@gmx.at>]

 > emacs -Q
 > M-x toggle-frame-fullscreen
 >
 > Place the mouse pointer on some element of the mode line and wait for
 > the tooltip. The tooltip frame is partially invisible because its top
 > left coordinates are determined from the mouse pointer position and, as
 > it is positioned near the bottom of the screen, there is no room left
 > for the tooltip.
 >
 > A tooltip may also be partially hidden because it has no enough
 > horizontal space when the mouse pointer is near the right edge of the
 > screen.

I cannot reproduce this.  In any case the calculations for the x- and
y-position of the tooltip take into account the size of the tooltip and
the width and height of the display as can be easily seen from the code
of compute_tip_xy.  If you see any truncation of a tooltip at a certain
position, please step with GDB through the respective part of the code
to find out what happened.

 > The MS Windows port places the tooltips taking into account the screen
 > edges.

So does the Lucid port.  Something else must be at work here.

martin