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comp.lang.ruby

calling winapi for EnumDisplayMonitors

Phil Smy

5/6/2009 11:59:00 AM

I am trying to write a desktop application in Ruby. We need to find out
what monitors are attached to the XP machine this will run on.
I looked at how SWT does this and it is accomplished via calling
EnumDisplayMonitors (windows api).

I cannot figure out how to call this from within Ruby using Win32API.
EnumDisplayMonitors's api is this:
BOOL EnumDisplayMonitors(
HDC hdc,
LPCRECT lprcClip,
MONITORENUMPROC lpfnEnum,
LPARAM dwData
);

How can I supply a proc? Is what I want to do even possible?

Any help would be appreciated. All this kind of stuff is not very
clearly documented for the novice and I can't find any relevant samples.
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3 Answers

Heesob Park

5/6/2009 2:44:00 PM

0

Hi,

2009/5/6 Phil Smy <phil@philsmy.com>:
> I am trying to write a desktop application in Ruby. We need to find out
> what monitors are attached to the XP machine this will run on.
> I looked at how SWT does this and it is accomplished via calling
> EnumDisplayMonitors (windows api).
>
> I cannot figure out how to call this from within Ruby using Win32API.
> EnumDisplayMonitors's api is this:
> BOOL EnumDisplayMonitors(
> =C2=A0HDC hdc,
> =C2=A0LPCRECT lprcClip,
> =C2=A0MONITORENUMPROC lpfnEnum,
> =C2=A0LPARAM dwData
> );
>
> How can I supply a proc? Is what I want to do even possible?
>
> Any help would be appreciated. All this kind of stuff is not very
> clearly documented for the novice and I can't find any relevant samples.

As you know, Win32API doesn't support callback.
Try with Ruby/DL or win32-api gem.

Here is a win32-api sample:

require 'win32/api'

EnumDisplayMonitors =3D Win32::API.new('EnumDisplayMonitors', 'LPKL',
'B', 'user32')
GetMonitorInfo =3D Win32::API.new('GetMonitorInfo', 'LP', 'B', 'user32')

MyInfoEnumProc =3D Win32::API::Callback.new('LLPL','L') {
|hMonitor,hdcMonitor,lprcMonitor,dwData|
lpmi =3D [72].pack('L') + 0.chr * 68
GetMonitorInfo.call(hMonitor,lpmi)
info =3D lpmi.unpack('L10Z*')
puts "Name:#{info[10]}, Width:#{info[3]}, Height:#{info[4]} "
1
}

EnumDisplayMonitors.call(0, nil, MyInfoEnumProc, 0)


Regards,
Park Heesob

Roger Pack

5/6/2009 7:21:00 PM

0

Phil Smy wrote:
> I am trying to write a desktop application in Ruby. We need to find out
> what monitors are attached to the XP machine this will run on.
> I looked at how SWT does this and it is accomplished via calling
> EnumDisplayMonitors (windows api).

Ruby wmi is also quite nice (dunno if it helps here though).
http://betterlogic.com/rog...
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Phil Smy

5/7/2009 8:57:00 AM

0

Hi Park,
In short - you rule!
Thanks - this does exactly what we need. I guess I need to do some
reading up on win32-api to understand HOW it does it, but this is a
great start.
Much appreciated.

Heesob Park wrote:
> Here is a win32-api sample:
>
> require 'win32/api'
>
> EnumDisplayMonitors = Win32::API.new('EnumDisplayMonitors', 'LPKL',
> 'B', 'user32')
> GetMonitorInfo = Win32::API.new('GetMonitorInfo', 'LP', 'B', 'user32')
>
> MyInfoEnumProc = Win32::API::Callback.new('LLPL','L') {
> |hMonitor,hdcMonitor,lprcMonitor,dwData|
> lpmi = [72].pack('L') + 0.chr * 68
> GetMonitorInfo.call(hMonitor,lpmi)
> info = lpmi.unpack('L10Z*')
> puts "Name:#{info[10]}, Width:#{info[3]}, Height:#{info[4]} "
> 1
> }
>
> EnumDisplayMonitors.call(0, nil, MyInfoEnumProc, 0)
>
>
> Regards,
> Park Heesob

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