[GD-Windows] More multimon

[Brian H. <bri...@py...>]

Multi-monitor support is a bit of a mess.

Disregarding NT4 and Win95, which simply compound problems across=
 the 
board because of lack of native multi-monitor support, it's still=
 a 
mess.

I don't even really have questions, I'm just posting this to see=
 if 
anyone has an opinion.

Using a GF4 Ti4200 w/ dual-head as my reference on Win2K, I have=
 
found out the following.

In a default installation, the NVidia driver reports to the=
 system 
that it's actually a single device with a single monitor.  This=
 means 
GetSystemMetrics( SM_CMONITORS ) returns 1; and=
 EnumDisplayMonitors() 
also only finds a single monitor.  EnumDisplayDevices() will only=
 
show a single display device, and within that device you will=
 only 
find a single monitor represented.

For all intents and purposes, the default dual-head install with=
 the 
NVidia drivers looks exactly like a widescreen single head system=
 
(2560x1024 in my case).  Thus any window that is centered will=
 end up 
getting chopped in half (although there are options in the=
 control 
panel to force dialogs, etc. to go to one monitor or another).

In addition, going "full screen" will shut off one monitor.  Not=
 to 
mention that trying to infer the right "native" resolution is=
 going 
to be tough.  For example, if you want to run 1024x768 but=
 centered 
in a 1280x1024 LCD fullscreen session (to avoid interpolation 
artifacts) there's simply no way to really to do that.  The best=
 you 
can do is run in a window and hope the user doesn't mind; or=
 force to 
1024x768 and hope it's not too ugly; or try to infer with some 
complicated heuristics what the best video resolution might be,=
 but 
even then you're never quite sure which monitor it's going to=
 select 
(e.g. I have a 17" LCD and a 21" CRT, the former supports up to 
1280x1024 and the latter goes up to 1600x1200).

Now, all that ugliness aside, if you solve it there you're still=
 in 
for trouble if the drivers have the "Treat each display as a=
 separate 
device" check box enabled in the control panel.

When THAT is enabled you can see that there are multiple monitors=
 
(thankfully).  Both GetSystemMetrics and EnumDisplayMonitors=
 report 
the right information.

Unfortunately there are now duplicated entries in the global=
 device 
list.  The display adapter will show up twice, with identical 
properties, one time as primary and another time as secondary. =
 And 
each of these instances will think it has FOUR monitors attached,=
 two 
for standard and two for Plug'n'Play.

I haven't figured out a clean way to discard a secondary if I=
 know 
that it's just an alias for the primary (there aren't any=
 duplicated 
fields).  Limiting to primary only then turns around and hoses=
 those 
people with an AGP + PCI configuration and who want stuff to run=
 on 
the secondary.

If I limit to primary only, then a lot of things get simplified,=
 but 
I'm not sure if that's really a good thing, since on some systems=
 the 
BIOS defaults to making PCI the primary device, which obviously=
 is 
not what you'd want in most cases.

I haven't even sat down and tried to sort out what happens on a 
Matrox G550 or Parhelia, or an AGP + PCI configuration.  

I also haven't investigated DirectX's capabilities either, since=
 it 
varies depending on the version (and just browsing the docs, it=
 seems 
like it assumes a 1:1 correlation between adapter and monitors,=
 so 
I'm guessing multihead cards have to present "virtual" adapters=
 to 
the system).

Bah.

When I get this all sorted I'll work out a flow chart.  It won't=
 be 
pretty.

Brian