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". However, the WH_MOUSE_LL hook is not injected into another process. Instead, the context switches back to the process that installed the hook and it is called in its original context. Then the context switches back to the application that generated the event.
The HOOKPROC type defines a pointer to this callback function. LowLevelMouseProc is a placeholder for the application-defined or library-defined function name.
Syntax
LRESULT CALLBACK LowLevelMouseProc( int nCode, WPARAM wParam, LPARAM lParam );
Parameters
nCode [in] Specifies a code the hook procedure uses to determine how to process the 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. This parameter can be one of the following values. HC_ACTIONThe wParam and lParam parameters contain information about a mouse message.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_MOUSEHWHEEL, WM_RBUTTONDOWN, or WM_RBUTTONUP. lParam [in] Pointer to an MSLLHOOKSTRUCT structure.
HC_ACTION
Return Value
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.
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\DesktopThe 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 cannot track this type of hook.
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.
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 cannot track this type of hook.
Function Information
HeaderDeclared in Winuser.h, include Windows.hImport libraryNoneMinimum operating systems Windows NT 4.0 SP3
See Also
Hooks Overview, CallNextHookEx, mouse_event, MSLLHOOKSTRUCT, SetWindowsHookEx, WH_MOUSE_LL, WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_RBUTTONDOWN, WM_RBUTTONUP
Public Delegate Function LowLevelMouseProc(ByVal nCode As LowLevelKeyboardProcHookCode, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As IntPtr
Public Enum LowLevelKeyboardProcHookCode As Integer ACTION = 0End Enum
Note: Signature is same os for LowLevelKeyboardProc.
LRESULT CALLBACK LowLevelMouseProc(int nCode,WPARAM wParam,LPARAM lParam){static bool hasBeenEntered = false;if(hasBeenEntered){//Prevent the mouse event being sent to other hook procs and the window procedure.//Might not be what you want.return 1;}hasBeenEntered = true;//acquire lock, call windows API functionshasBeenEntered = false; return CallNextHookEx(...);}