require 'win32/api'
require 'cstruct/win32struct'
 
include Win32
 
WS_VISIBLE      = 0x10000000
WS_CAPTION      = 0x00C00000
WS_SYSMENU      = 0x00080000
WS_MINIMIZEBOX  = 0x00020000
WS_MAXIMIZEBOX  = 0x00010000
WS_THICKFRAME   = 0x00040000
WS_OVERLAPPED   = 0x00000000
 
WS_OVERLAPPEDWINDOW = (WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | WS_THICKFRAME | WS_MINIMIZEBOX | WS_MAXIMIZEBOX)
 
WM_CREATE       = 0x0001
WM_DESTROY      = 0x0002
WM_PAINT        = 0x000F
WM_CLOSE        = 0x0010
WM_COMMAND      = 0x0111
 
CS_VREDRAW      = 0x0001
CS_HREDRAW      = 0x0002
COLOR_WINDOW    = 5
 
CW_USEDEFAULT   = -2147483648 #0x80000000
 
SW_SHOW         = 5
SW_SHOWDEFAULT  = 10
 
Memset          = API.new('memset', 'PLL', 'L', 'msvcrt')
LocalAlloc      = API.new('LocalAlloc', 'LL', 'L', 'kernel32')
GetModuleHandle = API.new('GetModuleHandle', 'P', 'L', 'kernel32')
RegisterClass   = API.new('RegisterClass', 'P', 'L', 'user32')
RegisterClassEx = API.new('RegisterClassEx', 'P', 'L', 'user32')
CloseWindow     = API.new('CloseWindow', 'L', 'B', 'user32')
CreateWindowEx  = API.new('CreateWindowEx', 'LPPLIIIILLLL', 'L', 'user32')
ShowWindow      = API.new('ShowWindow', 'LL', 'B', 'user32')
UpdateWindow    = API.new('UpdateWindow', 'L', 'B', 'user32')
BeginPaint      = API.new('BeginPaint', 'LP', 'L', 'user32')
EndPaint        = API.new('EndPaint', 'LP', 'L', 'user32')
PostQuitMessage = API.new('PostQuitMessage', 'I', 'V', 'user32')
DefWindowProc   = API.new('DefWindowProc', 'LLLL', 'L', 'user32')
GetMessage      = API.new('GetMessage', 'PLII', 'L', 'user32')
DispatchMessage = API.new('DispatchMessage', 'P', 'L', 'user32')
TranslateMessage = API.new('TranslateMessage', 'P', 'B', 'user32')
TextOut         = API.new('TextOut', 'LLLPL', 'B', 'gdi32' );
 
class POINT < Win32Struct
    LONG    :x
    LONG    :y
end
 
class MSG < Win32Struct
    uint32  :hwnd
    UINT    :message
    WPARAM  :wParam
    LPARAM  :lParam
    DWORD   :time
    POINT   :pt
end
 
class WNDCLASSA < Win32Struct
    UINT    :style
    uint32  :lpfnWndProc
    int32   :cbClsExtra
    int32   :cbWndExtra
    HINSTANCE   :hInstance
    HICON   :hIcon
    HCURSOR :hCursor
    HBRUSH  :hbrBackground
    LPCSTR  :lpszMenuName
    LPCSTR  :lpszClassName
end
 
class RECT < Win32Struct
    LONG    :left
    LONG    :top
    LONG    :right
    LONG    :bottom
end
 
class PAINTSTRUCT < Win32Struct
    HDC     :hdc
    BOOL    :fErase
    RECT    :rcPaint
    BOOL    :fRestore
    BOOL    :fIncUpdate
    BYTE    :rgbReserved,[32]
end
 
@window_proc = API::Callback.new('LLLL', 'I') do |hwnd, msg, wparam, lparam|
    ret = 0
    strMessage = "Hello, Win32 GUI(Ruby) World!"
    case msg
    when WM_PAINT
        ps  = PAINTSTRUCT.new
        hdc = BeginPaint.call(hwnd, ps.data)
        TextOut.call(hdc, 0, 0, strMessage, strMessage.length);
        EndPaint.call(hwnd, ps.data)
    when WM_DESTROY
        PostQuitMessage.call(0)
    else 
        ret = DefWindowProc.call(hwnd, msg, wparam, lparam)
    end
    ret
end
 
def alloc_string_buffer init_string, max_length
    buffer_pointer = LocalAlloc.call(0, max_length)
    buffer_addr = buffer_pointer
    Memset.call(buffer_addr, 0, max_length)
 
    init_string.each_byte do |byte|  
        Memset.call(buffer_pointer, byte, 1)
        buffer_pointer += 1
    end  
    buffer_addr
end
 
def WinMain instance, cmd_show
    msg = MSG.new
 
    wc = WNDCLASSA.new
    wc.style         = 0
    wc.lpfnWndProc   = @window_proc.address
    wc.cbClsExtra    = 0
    wc.cbWndExtra    = 0
    wc.hInstance     = instance
    wc.hIcon         = 0
    wc.hCursor       = 0
    wc.hbrBackground = (COLOR_WINDOW+1)
    wc.lpszMenuName  = 0
    wc.lpszClassName = alloc_string_buffer 'helloWindow', 256
 
    RegisterClass.call(wc.data)
 
    hwnd = CreateWindowEx.call(
        0,
        "helloWindow",
        "Hello, World!",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        640,
        480,
        0,
        0,
        wc.hInstance,
        0
    )
 
    ShowWindow.call(hwnd, cmd_show)
    UpdateWindow.call(hwnd)
 
    while(GetMessage.call(msg.data, 0, 0, 0) > 0)
        TranslateMessage.call(msg.data)
        DispatchMessage.call(msg.data)
    end
 
end
 
def main
    instance = GetModuleHandle.call(0)
    WinMain instance, SW_SHOW
end
 
main

C:¥> gem install cstruct

C:¥> ruby hello.rb

+------------------------------------------+
|Hello, World!                    [_][~][X]|
+------------------------------------------+
|Hello, Win32 GUI(Ruby) World!             |
|                                          |
|                                          |
|                                          |
|                                          |
|                                          |
|                                          |
|                                          |
|                                          |
|                                          |
+------------------------------------------+