The WM_MBUTTONDOWN message is posted when the user presses the middle mouse button while the 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.
WM_MBUTTONDOWN
fwKeys = wParam; // key flags
xPos = LOWORD(lParam); // horizontal position of cursor
yPos = HIWORD(lParam); // vertical position of cursor
Parameters
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 the CTRL key is down. |
| MK_LBUTTON | Set if the left mouse button is down. |
| MK_MBUTTON | Set if the middle mouse button is down. |
| MK_RBUTTON | Set if the right mouse button is down. |
| MK_SHIFT | Set if the SHIFT key is down. |
xPos
Value of the low-order word of lParam. Specifies the x-coordinate of the 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 cursor. The coordinate is relative to the upper-left corner of the client area.
Return Values
If an application processes this message, it should return zero.
Remarks
An application can use the MAKEPOINTS macro to convert the lParam parameter to a POINTS structure.
See Also
GetCapture, MAKEPOINTS, POINTS, SetCapture, WM_MBUTTONDBLCLK, WM_MBUTTONUP