Delphi: grab window content that is hidden or minimized

Hi all!
I currently try to capture content of a specific Window that does not have focus.
This is a direct3d application

Currently working but when capturing this window, if another is on the front, i have this fronted window on my screenshot (that normal)

But I want to be able to capture a screenshot of this window even if another is on the front and get exact image capture of this window.

Any idea?

Currently I use this code:

procedure TFRM_Main.Grab(bm: TBitMap; gt : GrabType);
var
  h: THandle;
  hdcSrc : THandle;
  var WoWHandle : THandle; // handle global de wow
classname: array[0..255] of char; // class du handle de wow
begin
  case(gt) of
    GTWINDOW : h := GetForeGroundWindow;
    GTSCREEN : h := GetDesktopWindow;
  else h := 0;
  end;
  try
    if h <> 0 then
    begin
      WoWHandle := FindWindow(nil,'My Direct3D App');
      GetClassName(WoWHandle,ClassName,SizeOf(ClassName));
      h := FindWindow(classname,nil);
      hdcSrc := GetWindowDC(h);
      GetWindowRect(h, SourceRect);
      bm.PixelFormat:=pf4bit;
      bm.Width  := SourceRect.Right - SourceRect.Left;
      bm.Height := SourceRect.Bottom - SourceRect.Top;
      DestRect := Rect(0, 0,
            SourceRect.Right - SourceRect.Left,
            SourceRect.Bottom - SourceRect.Top);
      StretchBlt(bm.Canvas.Handle, 0, 0, bm.Width,
            bm.Height, hdcSrc, 0, 0,bm.Width,bm.Height,
            SRCCOPY);
      end;
  finally
    ReleaseDC(0, hdcSrc);
  end;
end;

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