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

[martin rudalics]

> Have you tried Company?

No.

> This issue is about completion popup, which displays completions in the 
current buffer and window, in a rectangle rendered using an overlay. There are 
screenshots in that issue thread.
>
> Before the popup is rendered, we need to determine how much of it would fit 
below the current line, and if there's not enough space, we render it above the 
current line.

Aha... Could you try whether `window-text-pixel-size' could be used for
that?  IIUC you'd have to call it twice: Once for calculating how much
space you need and once for how much space is left below the current
line.  `window-text-height' with PIXELWISE t should give you the overall
height of the window.

> Even if the buffer is shorter than the window, we can temporarily pad it, so 
when calculating the height of the window, we need to take the whole of it into 
account. That's why `count-screen-line' doesn't seem like a good approach either.

If things like line spacing are involved you really should calculate
pixelwise.

martin