WM_NCLBUTTONDOWN message

Posted when the user presses the left 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.

#define WM_NCLBUTTONDOWN                0x00A1

wParam

The hit-test value returned by the DefWindowProc function as a result of processing the WM_NCHITTEST message. For a list of hit-test values, see WM_NCHITTEST.

lParam

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.

The DefWindowProc function tests the specified point to find the location of the cursor and performs the appropriate action. If appropriate, DefWindowProc sends the WM_SYSCOMMAND message to the window.

You can also use the GET_X_LPARAM and GET_Y_LPARAM macros to extract the values of the x- and y- coordinates from lParam.

xPos = GET_X_LPARAM(lParam); 
yPos = GET_Y_LPARAM(lParam); 

Reference

DefWindowProc

GET_X_LPARAM

GET_Y_LPARAM

WM_NCHITTEST

WM_NCLBUTTONDBLCLK

WM_NCLBUTTONUP

WM_SYSCOMMAND

Conceptual

Mouse Input

Other Resources

MAKEPOINTS

POINTS