Calling winapi for EnumDisplayMonitors

Ruby
1

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.

2

Hi,

2009/5/6 Phil S. [email protected]:

 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.

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 = 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 H.

3

Phil S. 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/roger/?p=1291

4

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 P. 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 H.