WM_MBUTTONDOWN
fwKeys = wParam; /* key flags */
xPos = LOWORD(lParam); /* horizontal position of cursor */
yPos = HIWORD(lParam); /* vertical position of cursor */
The WM_MBUTTONDOWN message is posted when the user presses the middle mouse button while the mouse cursor is in the client area of a window. If the mouse is not captured, the message is posted to the window beneath the cursor. Otherwise, the message is posted to the window that has captured the mouse.
fwKeys
Value of wParam. Indicates whether various virtual keys are down. This parameter can be any combination of the following values:
| Value | Description |
| MK_CONTROL | Set if CTRL key is down. |
| MK_LBUTTON | Set if left mouse button is down. |
| MK_RBUTTON | Set if right mouse button is down. |
| MK_SHIFT | Set if SHIFT key is down. |
xPos
Value of the low-order word of lParam. Specifies the x-coordinate of the mouse cursor. The coordinate is relative to the upper-left corner of the client area.
yPos
Value of the high-order word of lParam. Specifies the y-coordinate of the mouse cursor. The coordinate is relative to the upper-left corner of the client area.
An application should return zero if it processes this message.
An application can use the MAKEPOINTS macro to convert the lParam parameter to a POINTS structure.
GetCapture, SetCapture, WM_MBUTTONDBLCLK, WM_MBUTTONUP