Posted when the user presses the first or second X 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.
A window receives this message through its WindowProc function.
The low-order word indicates whether various virtual keys are down. It can be one or more of the following values.
The high-order word indicates which button was clicked. It can be one of the following values.
The first X button was clicked.
The second X button was clicked.
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.
If an application processes this message, it should return TRUE. For more information about processing the return value, see the Remarks section.
Use the following code to get the information in the wParam parameter:
fwKeys = GET_KEYSTATE_WPARAM (wParam); fwButton = GET_XBUTTON_WPARAM (wParam);
Use the following code to obtain the horizontal and vertical position:
xPos = GET_X_LPARAM(lParam); yPos = GET_Y_LPARAM(lParam);
As noted above, the x-coordinate is in the low-order short of the return value; the y-coordinate is in the high-order short (both represent signed values because they can take negative values on systems with multiple monitors). If the return value is assigned to a variable, you can use the MAKEPOINTS macro to obtain a POINTS structure from the return value. You can also use the GET_X_LPARAM or GET_Y_LPARAM macro to extract the x- or y-coordinate.
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.
Unlike the WM_LBUTTONDOWN, WM_MBUTTONDOWN, and WM_RBUTTONDOWN messages, an application should return TRUE from this message if it processes it. Doing so allows software that simulates this message on Windows systems earlier than Windows 2000 to determine whether the window procedure processed the message or called DefWindowProc to process it.
Minimum supported client
|Windows 2000 Professional [desktop apps only]|
Minimum supported server
|Windows 2000 Server [desktop apps only]|
- Mouse Input
- Other Resources
Build date: 11/16/2013