Capture Client Area from Window

#include <WinAPI.au3>
#include <GDIPlus.au3>
#include <Array.au3>

$hWnd = GUICreate("Test", 400, 400)
$cButton1 = GUICtrlCreateButton("Test", 50, 50, 50, 25)
$cEdit = GUICtrlCreateEdit("AutoIt rocks!!", 50, 70, 200, 200)
GUISetState()

Sleep(500)

$hBMP = _ScreenCapture_CaptureWndEx($hWnd, -1, -1)

_GDIPlus_Startup()
$hBitmap = _GDIPlus_BitmapCreateFromHBITMAP($hBMP)
_GDIPlus_ImageSaveToFile($hBitmap, @DesktopDir & "\Test.png")
_GDIPlus_BitmapDispose($hBitmap)
_GDIPlus_Shutdown()

_WinAPI_DeleteObject($hBMP)

Do
Until GUIGetMsg() = -3

Func _ScreenCapture_CaptureWndEx($hWnd, $iWidth = -1, $iHeight = -1)
    If $iWidth = -1 Then $iWidth = _WinAPI_GetClientWidth($hWnd)
    If $iHeight = -1 Then $iHeight = _WinAPI_GetClientHeight($hWnd)

    Local $hDDC = _WinAPI_GetDC($hWnd)
    Local $hCDC = _WinAPI_CreateCompatibleDC($hDDC)
    Local $hBMP = _WinAPI_CreateCompatibleBitmap($hDDC, $iWidth, $iHeight)
    _WinAPI_SelectObject($hCDC, $hBMP)
    _WinAPI_BitBlt($hCDC, 0, 0, $iWidth, $iHeight, $hDDC, 0, 0, 0x00CC0020)

    _WinAPI_ReleaseDC($hWnd, $hDDC)
    _WinAPI_DeleteDC($hCDC)
    Return $hBMP
EndFunc