WM_XBUTTONDOWN message

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.

#define WM_XBUTTONDOWN                  0x020B

Parameters

wParam

The low-order word indicates whether various virtual keys are down. It can be one or more of the following values.

Value Meaning
MK_CONTROL
0x0008
The CTRL key is down.
MK_LBUTTON
0x0001
The left mouse button is down.
MK_MBUTTON
0x0010
The middle mouse button is down.
MK_RBUTTON
0x0002
The right mouse button is down.
MK_SHIFT
0x0004
The SHIFT key is down.
MK_XBUTTON1
0x0020
The first X button is down.
MK_XBUTTON2
0x0040
The second X button is down.

The high-order word indicates which button was clicked. It can be one of the following values.

Value Meaning
XBUTTON1
0x0001
The first X button was clicked.
XBUTTON2
0x0002
The second X button was clicked.

lParam

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.

Return value

If an application processes this message, it should return TRUE. For more information about processing the return value, see the Remarks section.

Remarks

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.

Requirements

Minimum supported client
Windows 2000 Professional [desktop apps only]
Minimum supported server
Windows 2000 Server [desktop apps only]
Header
Winuser.h (include Windowsx.h)

See also

Reference

GET_KEYSTATE_WPARAM

GET_X_LPARAM

GET_XBUTTON_WPARAM

GET_Y_LPARAM

GetCapture

SetCapture

WM_XBUTTONDBLCLK

WM_XBUTTONUP

Conceptual

Mouse Input

Other Resources

MAKEPOINTS

POINTS