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

[martin rudalics <rudalics@gmx.at>]

 > It won't help to determine how much space is left below the current line if the current line is the last in the buffer but not in the window, right?

You have to calculate the height of the text from window start till the
end of the buffer and subtract the result from the window's text height.

 >  > `window-text-height' with PIXELWISE t should give you the overall
 >  > height of the window.
 >
 > `count-screen-lines' already helps with "space above the current line", and we can find out the total height of the window in pixels. So if I'm going to do the arithmetics myself, the one thing missing is the accurate value of the height of a line in the buffer.

`count-screen-lines' doesn't return a pixel value.  How do you get that
with lines of different heights and line spacing?

 > How do I obtain it (let's consider it mostly-constant)?
 >
 >> If things like line spacing are involved you really should calculate
 >> pixelwise.
 >
 > The docstring of `window-screen-lines' seems to claim that it's suitable. The implementation looks kinda right, too, but the result it returns is not accurate.

It again just returns a line value.  IIRC someone has set the font size
to 1 pixel to make this return something reasonable.  But why do all
these acrobatics?  `window-text-pixel-size' should give you everything
you need in a uniform way.  And if something's missing we can easily add
it.

martin