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

[Eli Zaretskii]

> Date: Tue, 05 Aug 2014 16:38:36 +0200
> From: martin rudalics <rudalics@gmx.at>
> CC: dgutov@yandex.ru, 18195@debbugs.gnu.org
> 
>  >> Can you fix it so it simply works on the current buffer instead
>  >> of the window's buffer?
>  >
>  > Fix what exactly?  What is "it" in this context?
> 
> `window-text-pixel-size'.  Never mind.  I'll find a fix.

You'll need to designate a window anyway, since layout is impossible
without knowing in which window it will be done.

There's also the issue of the buffer text on which the text will be
overlaid: the dimensions of the screen lines to be (partially)
overlaid affect the pixel dimensions of the overlaying text.  So if
the buffer text uses different fonts, the text overlaid on it will
have different dimensions than the same text when displayed in its own
buffer.