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[New for Windows NT 4.0 Service Pack 3.]
The LowLevelMouseProc hook procedure is an application-defined or library-defined callback function the system calls every time a new mouse input event is about to be posted into a thread input queue. The system calls this hook before the event is processed.
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”.
LRESULT CALLBACK LowLevelMouseProc(
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int nCode, |
// hook code |
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WPARAM wParam, |
// message identifier |
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LPARAM lParam |
// pointer to structure with message data |
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); |
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Value |
Meaning |
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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.
To prevent the system from passing the message to the rest of the hook chain or to the target window procedure, the return value must be a nonzero value. To allow the system to pass the message to the target window procedure, bypassing the remaining procedures in the chain, the return value must be zero.
An application installs the hook procedure by specifying the WH_MOUSE_LL hook type and the address of 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.
CallNextHookEx, mouse_event, MSLLHOOKSTRUCT, SetWindowsHookEx, WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_RBUTTONDOWN, WM_RBUTTONUP.