[h-e-w] Multi-monitor support, display-pixel-width etc.

[Hannu Koivisto]

Greetings,

The documentation of display-pixel-width says:

"For graphical terminals, note that on "multi-monitor" setups this
refers to the pixel width for all physical monitors associated with
DISPLAY.  *Note Multiple Displays::."
          
I have a multi-monitor setup with two displays: according to
Windows' Display Properties -> Settings, the first one is 1050x1680
with its top left coordinate (-1048,-600) and the second one is
1920x1080 with its top left coordinate (0,0).  The second one is
marked as the primary display.

I'm not entirely sure what display-screens is supposed to return
(i.e. what is "screen" here) but in any case it returns 1.
display-pixel-width returns 1920 and display-pixel-height 1080,
i.e. the dimensions of the primary display.  I think this is not
what could be expected based on that documentation.

I do suspect that at least in my case simply changing
display-pixel-width to return 2970 and display-pixel-height 1680
wouldn't work.  One would also have to translate frame coordinates
(in my case frames that are completely visible may have negative
top left corner coordinates).  But I fear even that wouldn't be an
ideal solution, because then some coordinates (0..2970, 0..1680)
would be out of screen.  Also, you couldn't pass such coordinates
to external applications.

Maybe Emacs should provide some kind of interface through which one
could get information about multiple displays?

I faced this issue with Speedbar positioning code that works
incorrectly in my system.  I intend to fix it, but it seems I can't
get the needed information from Emacs at the moment.

-- 
Hannu