This message is posted to a window when user moves the mouse while pressing the left mouse button or moves the stylus while the tip is down. If another window does not capture the mouse stylus input, the OS posts the message to the window that contains the cursor or the stylus tip. If another window captures the mouse or stylus input, the OS posts the message to the window that has the capture.
WM_MOUSEMOVE fwKeys = wParam; xPos = LOWORD(lParam); yPos = HIWORD(lParam);
Indicates the mouse buttons and keys that the user pressed. The following table shows the possible values, which can be combined.
The user pressed the CTRL key.
The user pressed the left mouse button.
The user pressed the SHIFT key.
Value of the low-order word of lParam. Specifies the x-coordinate of the cursor, relative to the upper-left corner of the client area.
Value of the high-order word of lParam. Specifies the y-coordinate of the cursor, relative to the upper-left corner of the client area.