LowLevelMouseProc

The LowLevelMouseProc hook procedure is an application-defined or library-defined callback function used with the SetWindowsHookEx function. The system call this function every time a new mouse input event is about to be posted into a thread input queue. The mouse input can come from the local mouse driver or from calls to the mouse_event function. If the input comes from a call to mouse_event, the input was "injected".

The HOOKPROC type defines a pointer to this callback function. LowLevelMouseProc is a placeholder for the application-defined or library-defined function name.

LRESULT CALLBACK LowLevelMouseProc(
  int nCode,     // hook code
  WPARAM wParam, // message identifier
  LPARAM lParam  // message data
);

Parameters

nCode

[in] Specifies a code the hook procedure uses to determine how to process the message. This parameter can be one of the following values.

Value	Meaning
HC_ACTION	The wParam and lParam parameters contain information about a mouse message.

If nCode is less than zero, the hook procedure must pass the message to the CallNextHookEx function without further processing and should return the value returned by CallNextHookEx.

wParam

[in] Specifies the identifier of the mouse message. This parameter can be one of the following messages: WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_RBUTTONDOWN, or WM_RBUTTONUP.

lParam

[in] Pointer to an MSLLHOOKSTRUCT structure.

Return Values

If nCode is less than zero, the hook procedure must return the value returned by CallNextHookEx.

If nCode is greater than or equal to zero, and the hook procedure did not process the message, it is highly recommended that you call CallNextHookEx and return the value it returns; otherwise, other applications that have installed WH_MOUSE_LL hooks will not receive hook notifications and may behave incorrectly as a result. If the hook procedure processed the message, it may return a nonzero value to prevent the system from passing the message to the rest of the hook chain or the target window procedure.

Remarks

An application installs the hook procedure by specifying the WH_MOUSE_LL hook type and a pointer to the hook procedure in a call to the SetWindowsHookEx function.

This hook is called in the context of the thread that installed it. The call is made by sending a message to the thread that installed the hook. Therefore, the thread that installed the hook must have a message loop.

The hook procedure should process a message in less time than the data entry specified in the LowLevelHooksTimeout value in the following registry key:

HKEY_CURRENT_USER\Control Panel\Desktop

The value is in milliseconds. If the hook procedure does not return during this interval, the system will pass the message to the next hook.

Note that debug hooks can not track this type of hook.

Requirements

  Windows NT/2000: Requires Windows NT 4.0 SP3 or later.
  Windows 95/98: Unsupported.
  Header: Declared in Winuser.h; include Windows.h.

See Also

Hooks Overview, Hook Functions, CallNextHookEx, mouse_event, MSLLHOOKSTRUCT, SetWindowsHookEx, WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_RBUTTONDOWN, WM_RBUTTONUP