The WM_LBUTTONDOWN message is posted when the user presses the left 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.
A window receives this message through its WindowProc function.
Syntax
WM_LBUTTONDOWN
WPARAM wParam
LPARAM lParam;
Parameters
- wParam
-
Indicates whether various virtual keys are down. This parameter can be one or more of the following values.
MK_CONTROL- The CTRL key is down.
MK_LBUTTON- The left mouse button is down.
MK_MBUTTON- The middle mouse button is down.
MK_RBUTTON- The right mouse button is down.
MK_SHIFT- The SHIFT key is down.
MK_XBUTTON1- Windows 2000/XP: The first X button is down.
MK_XBUTTON2- Windows 2000/XP: The second X button is down.
- 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 zero.
Remarks
Use the following code to obtain the horizontal and vertical position:
xPos = GET_X_LPARAM(lParam);
yPos = GET_Y_LPARAM(lParam);
You can also use the MAKEPOINTS macro to convert the
lParam parameter to a POINTS structure.
To detect that the ALT key was pressed, check whether GetKeyState(VK_MENU) < 0. Note, this must not be
GetAsyncKeyState.
Notification Requirements
| Minimum DLL Version |
None |
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| Header | Declared in Winuser.h, include Windows.h |
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| Minimum operating systems |
Windows 95, Windows NT 3.1 |
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See Also