The WM_MOUSEMOVE message is posted to a window when the cursor moves. If the mouse is not captured, the message is posted to the window that contains the cursor. Otherwise, the message is posted to the window that has captured the mouse.
A window receives this message through its WindowProc function.


Parameters
wParam
Indicates whether various virtual keys are down. This parameter can be one or more of the following values. Value Description
MK_CONTROL The CTRL key is down.
MK_LBUTTON The left mouse button is down.
MK_MBUTTON The middle mouse button is down.
MK_RBUTTON The right mouse button is down.
MK_SHIFT The SHIFT key is down.

lParam
The low-order word specifies the x-coordinate of the cursor. The coordinate is relative to the upper-left corner of the client area.
The high-order word specifies the y-coordinate of the cursor. The coordinate is relative to the upper-left corner of the client area.

Remarks
Use the following code to obtain the horizontal and vertical position:

You can also use the MAKEPOINTS macro to convert the lParam parameter to a POINTS structure.