Re: ffi - Popping image on top of the screen

If it's OK to use a Microsoft Windows MsgBox which a user will have to
close manually then the following may help. (It might be possible to
use something like SendKeys to close the MsgBox from Ruby.)

It seems to work both with MRI Ruby ruby.exe in a console window and
with MRI Ruby rubyw.exe (no console window, but as my trying that may
be the first time I've ever used rubyw.exe, no guarantees!).


# a longer example is here:
# http://www.pastie.org/4074156

# For a Microsoft Windows MsgBox the basic idea is like this for MRI Ruby 1.9:

  require 'dl'
  User32 = DL.dlopen('user32')
  User32_MsgBox =
        DL::CFunc.new( User32[ 'MessageBoxA' ], DL::TYPE_LONG, 'MessageBox')

  def MsgBox(text, title = "", buttons_icon_etc=0, timeout=0, handle=nil)
    if (timeout == 0 || ! timeout) && ! handle then
      # User32_MsgBox.call returns an array:
      #   [return_value, [0, text, title, buttons + icon + modality]]
      # we only want the return value, hence "result, ="
      # #dup used: if text or title are frozen, #pack('p') raises an exception
      result, = User32_MsgBox.call( [ 0, text.dup, title.dup,
                          buttons_icon_etc ].pack('L!ppL!').unpack('L!*') )
      return result
    end
    raise "MsgBox: to use timeout or handle may need something like AutoIt"
  end

  MsgBox("basic text then title Microsoft Windows MsgBox example" <<
         "\ntried in 1.9 but not 1.8",
         "title is ruby " + RUBY_VERSION.to_s)