WM_LBUTTONDOWN Notification
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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.
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.