Re: tooltip can be displayed outside the screen

[Juri Linkov <juri@jurta.org>]

> It must be a bug that the tooltip can be covered by the pointer so
> I've changed it as you suggested (for W32 and Mac also this time).
> You must have quite a big font to see this with the default y offset.
> I also changed the default y offset to 20 from 40.

Thanks.  Now due to your changes I discovered an old bug (I can reproduce
it in Emacs 21.4) in X coordinate calculations (and now this bug also
affects Y coordinate calculations).  After setting the X offset
(or the Y offset) to a negative value, tooltips can appear partly
outside the left (or top) edge of the screen.  I'm sorry, I didn't
report this bug earlier, because I found it only now, after your
changes while trying to use negative offsets.

One idea that came to me is that negative offsets could be interpreted
as absolute distances between the X (Y) position of the mouse and the
right (bottom) border of the tooltip frame (and to leave positive offsets
relative to the left (top) border as they work now).  This way no matter
what values offsets will have, the tooltip frame will never cover the mouse
pointer.  And this will work exactly the same way as currently calculations
behave to avoid the tooltip displayed outside the screen (i.e. negating the
interpretation of offsets to opposite sides of the tooltip frame).

-- 
Juri Linkov
http://www.jurta.org/emacs/