bug#15336: Bad computation of window height

[Eli Zaretskii <eliz@gnu.org>]

> From: Sebastien Vauban <sva-news@mygooglest.com>
> Date: Fri, 24 Oct 2014 16:16:27 +0200
> 
> One side note though: I have 2 screens, and they are set up one above
> the other (physically and logically).
> 
>   |----------------------|
>   | screen #2 (external) |  <-- 1680 x 1050
>   |----------------------|
>   | screen #1 (laptop)   |  <-- 1920 x 1080 (Full HD)
>   |----------------------|
> 
> That may impact what I see on Emacs 25.0.50.1.
> 
> With the following code:
> 
> --8<---------------cut here---------------start------------->8---
>   (when (display-graphic-p)
> 
>     ;; put Emacs exactly where you want it, every time it starts up
>     (setq initial-frame-alist '((top . 0) (left . 0)))
> 
>     ;; auto-detect the screen dimensions and compute the height of Emacs
>     (add-to-list 'default-frame-alist
>                  (cons 'height
>                        (/ (- (x-display-pixel-height) 106)
>                           (frame-char-height))))
> 
>     ;; maximize Emacs by default
>     (modify-all-frames-parameters '((fullscreen . maximized))))
> --8<---------------cut here---------------end--------------->8---
> 
> I'm expecting to have Emacs maximized at startup, on the main screen,
> that is occupying the full space of screen #1: 1920 x 1080.
> 
> What I get, instead, is an Emacs frame of (1680 + 1920) x 1080... whose
> top-right corner is located at the top-right corner of screen #1 (hence,
> I don't even see its full height, without minimizing and re-maximizing
> it first).

I'm guessing that the coordinates (0, 0) are on screen #1, in which
case you are getting what you asked for: a frame whose top-left corner
is on screen #1.

When using several monitors connected to the same machine, you
shouldn't assume that the top-left corner of the virtual screen has
the coordinates (0, 0).

What does the function display-monitor-attributes-list return?