Posted when the user presses the middle mouse button while the cursor is within the nonclient area of a window. This message is posted to the window that contains the cursor. If a window has captured the mouse, this message is not posted.
A window receives this message through its WindowProc function.
A POINTS structure that contains the x- and y-coordinates of the cursor. The coordinates are relative to the upper-left corner of the screen.
If an application processes this message, it should return zero.
xPos = GET_X_LPARAM(lParam); yPos = GET_Y_LPARAM(lParam);
Important Do not use the LOWORD or HIWORD macros to extract the x- and y- coordinates of the cursor position because these macros return incorrect results on systems with multiple monitors. Systems with multiple monitors can have negative x- and y- coordinates, and LOWORD and HIWORD treat the coordinates as unsigned quantities.
If it is appropriate to do so, the system sends the WM_SYSCOMMAND message to the window.
Minimum supported client
|Windows 2000 Professional [desktop apps only]|
Minimum supported server
|Windows 2000 Server [desktop apps only]|
- Mouse Input
- Other Resources