From ReactOS

typedef struct _EDD_DIRECTDRAW_GLOBAL
{
/* 0x000 */    PVOID dhpdev;           /* The assign pdev */
/* 0x004 */    DWORD dwReserved1;
/* 0x008 */    DWORD dwReserved2;
/* 0x00C */    ULONG unk_000c[3];
/* 0x018 */    LONG cDriverReferences;
/* 0x01C */    ULONG unk_01c[3];
/* 0x028 */    LONGLONG llAssertModeTimeout;
/* 0x030 */    DWORD dwNumHeaps;
/* 0x034 */    VIDEOMEMORY *pvmList;
/* 0x038 */    DWORD dwNumFourCC;
/* 0x03C */    PDWORD pdwFourCC;
/* 0x040 */    DD_HALINFO ddHalInfo;
/* 0x1E0 */    ULONG unk_1e0[44];
/* 0x290 */    DD_CALLBACKS ddCallbacks;
/* 0x2C4 */    DD_SURFACECALLBACKS ddSurfaceCallbacks;
/* 0x304 */    DD_PALETTECALLBACKS ddPaletteCallbacks;
/* 0x314 */    ULONG unk_314[48];
/* 0x3D4 */    D3DNTHAL_CALLBACKS d3dNtHalCallbacks;
/* 0x460 */    ULONG unk_460[7];
/* 0x47C */    D3DNTHAL_CALLBACKS2 d3dNtHalCallbacks2;
/* 0x498 */    ULONG unk_498[18];
/* 0x4E0 */    DD_MISCELLANEOUSCALLBACKS ddMiscellanousCallbacks;
/* 0x4EC */    ULONG unk_4ec[18];
/* 0x534 */    D3DNTHAL_CALLBACKS3 d3dNtHalCallbacks3;
/* 0x54C */    ULONG unk_54c[23];
/* 0x5A8 */    EDD_DIRECTDRAW_LOCAL* peDirectDrawLocalList;
/* 0x5ac */    EDD_SURFACE* peSurface_LockList;
/* 0x5B0 */    FLONG fl;
/* 0x5B4 */    ULONG cSurfaceLocks;
/* 0x5B8 */    PKEVENT pAssertModeEvent;
/* 0x5Bc */    EDD_SURFACE *peSurfaceCurrent;
/* 0x5C0 */    EDD_SURFACE *peSurfacePrimary;
/* 0x5C4 */    BOOL bSuspended;
/* 0x5C8 */    ULONG unk_5c8[12];
/* 0x5F8 */    RECTL rcbounds;
/* 0x608 */    HDEV hDev;
/* 0x60c */    PVOID hPDev;  
} EDD_DIRECTDRAW_GLOBAL, *PEDD_DIRECTDRAW_GLOBAL;

partly updated for windows xp and windows 2003, the above struct is from yaun book

NOTE : if any of these flags are set in dwCallbackFlags (struct EDD_DIRECTDRAW_GLOBAL), it means that the respective callback member for it has been filled in by a graphic driver

1. define EDDDGBL_MISCCALLBACKS 0x01 // ddMiscellanousCallbacks
2. define EDDDGBL_VIDEOPORTCALLBACKS 0x02 // ddVideoPortCallback
3. define EDDDGBL_MISC2CALLBACKS 0x80 // ddMiscellanous2Callbacks

typedef struct _EDD_DIRECTDRAW_GLOBAL
{
/* 0x000 */    PVOID dhpdev;           // 0x000 <-- verified to match Windows XP, dhpdev, the drv hPDev --> 
/* 0x004 */    DWORD dwReserved1;
/* 0x008 */    DWORD dwReserved2;
/* 0x00C */    ULONG unk_000c[3];
/* 0x018 */    LONG cDriverReferences;
/* 0x01C */    ULONG unk_01c;
/* 0x020 */    DWORD dwCallbackFlags;  // 0x020 <-- verified to match Windows XP, dwCallbackFlags
                                                                               
/* 0x024 */    ULONG unk_024;
/* 0x028 */    PVOID   llAssertModeTimeout;                           // 0x028 <-- verified to match Windows XP, llAssertModeTimeout, it is a function call llAssertModeTimeout
                                                                        
/* 0x030 */    DWORD dwNumHeaps;                                       // 0x030 <-- verified to match Windows XP, dwNumHeaps
/* 0x034 */    VIDEOMEMORY *pvmList;                                   // 0x034 <-- verified to match Windows XP, pvmList
/* 0x038 */    DWORD dwNumFourCC;
/* 0x03C */    PDWORD pdwFourCC;
/* 0x040 */    DD_HALINFO ddHalInfo;                                   // 0x040 <-- verified to match Windows XP, ddHalInfo
/* 0x1E0 */    ULONG unk_1e0[46];
/* 0x298 */    DD_CALLBACKS ddCallbacks;                               // 0x298 <-- verified to match Windows XP, ddCallbacks
/* 0x2C4 */    DD_SURFACECALLBACKS ddSurfaceCallbacks;                 // 0x2C4 <-- verified to match Windows XP, ddSurfaceCallbacks
/* 0x300 */    DD_PALETTECALLBACKS ddPaletteCallbacks;                 // 0x300 <-- verified to match Windows XP, ddPaletteCallbacks
/* 0x314 */    D3DNTHAL_GLOBALDRIVERDATA d3dNtGlobalDriverData           // 0x314 <-- verified to match Windows XP, d3dNtGlobalDriverData                          
/* 0x3D4 */    D3DNTHAL_CALLBACKS d3dNtHalCallbacks;
/* 0x460 */    ULONG unk_460[9];
/* 0x47C */    D3DNTHAL_CALLBACKS2 d3dNtHalCallbacks2;
/* 0x498 */    DD_VIDEOPORTCALLBACKS ddVideoPortCallback;              // 0x498 <-- verified to match Windows XP, ddVideoPortCallback
/* 0x4E0 */    DD_MISCELLANEOUSCALLBACKS ddMiscellanousCallbacks;      // 0x4E0 <-- verified to match Windows XP, ddMiscellanousCallbacks
/* 0x4EC */    DD_MISCELLANEOUS2CALLBACKS ddMiscellanous2Callbacks;    // 0x4EC <-- verified to match Windows XP, ddMiscellanous2Callbacks
/* 0x504 */    ULONG unk_504[10];
/* 0x534 */    D3DNTHAL_CALLBACKS3 d3dNtHalCallbacks3;
/* 0x5A4 */    ULONG unk_544;
/* 0x5A8 */    ULONG unk_548;
/* 0x54C */    ULONG unk_54c[23];
/* 0x5A8 */    EDD_DIRECTDRAW_LOCAL* peDirectDrawLocalList; // 0x5A8 <-- verified to match Windows XP, it is a current local struct, not a list,  peDirectDrawLocalList Current
/* 0x5ac */    EDD_SURFACE* peSurface_LockList;
/* 0x5B0 */    FLONG fl;
/* 0x5B4 */    ULONG cSurfaceLocks;
/* 0x5B8 */    PKEVENT pAssertModeEvent;
/* 0x5Bc */    EDD_SURFACE *peSurfaceCurrent;
/* 0x5C0 */    EDD_SURFACE *peSurfacePrimary;
/* 0x5C4 */    BOOL bSuspended;                             // 0x5C4 <-- verified to match Windows XP, tells dxg to use driver's own api or return error code instead 
/* 0x5C8 */    ULONG unk_5c8[12];
/* 0x5F8 */    RECTL rcbounds;
/* 0x608 */    ULONG unk_608;
/* 0x60c */    HDEV hDev;                                   // 0x60c <-- verified to match Windows XP, The real Pdev, hDev
} EDD_DIRECTDRAW_GLOBAL, *PEDD_DIRECTDRAW_GLOBAL;