Using a slightly modified example from _GDIPlus_BitmapCreateFromScan0() :
#include <GDIPlus.au3>
#include <GUIConstantsEx.au3>
Example()
Func Example()
_GDIPlus_Startup()
Local Const $iW = 500, $iH = 500
Local $hGui = GUICreate("", $iW, $iH)
GUISetState()
Local $hGraphics = _GDIPlus_GraphicsCreateFromHWND($hGui)
Local $tPixel = DllStructCreate("uint[" & $iW * $iH & "];")
Local $iOffset