Techwiki:Win32k/BASEOBJECT
The GDI Base Object, which is a header at the top of every GDI Object. The structure is called _DD_BASEOBJECT and is defined as follows for Windows XP and Windows 2003 :
typedef struct _BASEOBJECT { HANDLE hHmgr; ULONG cCount; // 0x4 <- No longer a pointer. LONG cExclusiveLock; PW32THREAD Tid; } BASEOBJECT, *POBJ, DD_BASEOBJECT, *PDD_BASEOBJECT;
The pointer to a _BASEOBJECT is known as a POBJ.