Re: display-mm-width return value off on Windows

[Eli Zaretskii <eliz@gnu.org>]

> From: Ralf Angeli <angeli@caeruleus.net>
> Date: Thu, 06 Jul 2006 19:50:26 +0200
> 
> On Windows the return values of `display-mm-width' and
> `display-mm-height' don't really reflect the screen width and height
> in millimeters.  I attached a patch which yields more realistic
> results.

Thanks.

> In my case:
> 
>                    display-mm-*   display-mm-*
>         Real size  without patch  with patch
> Width   285mm      370            279
> Height  215mm      277            203
> 
> For a preview-latex user who originally reported the problem:
> 
>                    display-mm-*   display-mm-*
>         Real size  without patch  with patch
> Width   330mm      320            305
> Height  207mm      240            203

That is still not a very good approximation, is it?

> -  cap = GetDeviceCaps (hdc, VERTSIZE);
> +  height = round (GetDeviceCaps (hdc, VERTRES)
> +		  / GetDeviceCaps (hdc, LOGPIXELSY) * 25.4);

What is this magic constant 25.4?  I think we at least should use a
single macro instead of having the literal constant scattered across
the sources.