bug#18195: 24.3.92; window-screen-lines is not accurate

[martin rudalics <rudalics@gmx.at>]

 > It shouldn't.  But AFAIU, this is not what is wanted here, because the
 > problem is where in the buffer to put the overlay.  In the above
 > example, you put it at point-min, but that position needs to be
 > _computed_ based on the pixel-size of the text to be put in the
 > overlay.

I'd put the overlay at the desired position right away and check whether
it fits (usually it should).  If it doesn't, I'd have to remove it and
put it somewhere else.  I can't imagine a solution where multiple
attempts could be avoided.  After all, one prior aim seems to be that a
certain line of the original text must not be covered by the overlay.
Hence, neither aligning the overlay at the bottom or top line of a
window seem to work always.

 > IOW, your suggested solution is incomplete, unless you intend the
 > application to do some iterative process, each time changing the
 > position where it puts the overlay and adjusting it in the next
 > iteration based on the results of window-text-pixel-size.

This precisley formulates what the application should do and cannot be
avoided IMHO.  After all, tooltips and menus seem to face exactly the
same problem when the frame is at the bottom of the display.  Otherwise,
these are better off since they can are not constrained by the edges of
the window.

martin