## Simple Types

This section contains information about the following simple types defined for use with Active Accessibility.

- DDIHOOKPROC
- DDITYPE
- HDDI
- HWINEVENTHOOK
- LPDDIPARAMS
- WINEVENTPROC

### DDIHOOKPROC

The DDIHOOKPROC type defines a variable that points to a valid DDI hook callback procedure. The winddi.h header file uses the following definition.

    typedef DWORD (CALLBACK* DDIHOOKPROC)(HDDI, LONG, DDITYPE, LPDDIPARAMS);

For more information, see DDIHookProc.

### DDITYPE

The DDITYPE type defines a variable describing a specific DDI function call. The winddi.h header file uses the following definition.

    typedef UINT    DDITYPE;

This data type is used with the CallNextDDI function and the DDIHookProc callback function.

### HDDI

The HDDI type defines a 32-bit variable that identifies a DDI hook. The winddi.h header file uses the following definition.

    typedef struct tagDDI FAR* HDDI;

This data type is used with the CallNextDDI, SetDDIHook, and UnhookDDIHook functions.

### HWINEVENTHOOK

The HWINEVENTHOOK type defines a 32-bit variable that identifies a window event hook. The winable.h header file uses the following definition.

    typedef DWORD HWINEVENTHOOK

This data type is used with the WinEventProc, SetWinEventHook, and UnhookWinEvent functions.

### LPDDIPARAMS

The LPDDIPARAMS type defines a variable that contains the address of one of the DDI parameter structures. The DDI parameters structures are included in the winddi.h header file, which defines LPDDIPARAMS as follows:

    typedef LPVOID  LPDDIPARAMS;

This data type is used with CallNextDDI function and the DDIHookProc callback function.

### WINEVENTPROC

The WINEVENTPROC type defines a variable that conforms to the WinEventProc callback function declaration. The winable.h header file uses the following definition.

    typedef VOID (CALLBACK* WINEVENTPROC)(
        HWINEVENTHOOK  hWinEventHook,
        DWORD          event,
        HWND           hwnd,
        LONG           idObject,
        LONG           idChild,
        DWORD          idEventThread,
        DWORD          dwmsEventTime);

For more information, see WinEventProc.

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