The WM_NCHITTEST message is sent to a window when the cursor moves, or when a mouse button is pressed or released. If the mouse is not captured, the message is sent to the window beneath the cursor. Otherwise, the message is sent to the window that has captured the mouse.

A window receives this message through its WindowProc function.

Syntax

WM_NCHITTEST

    WPARAM wParam
    LPARAM lParam;
    

Parameters

wParam

This parameter is not used.

lParam

The low-order word specifies the x-coordinate of the cursor. The coordinate is relative to the upper-left corner of the screen.

The high-order word specifies the y-coordinate of the cursor. The coordinate is relative to the upper-left corner of the screen.

Return Value

The return value of the DefWindowProc function is one of the following values, indicating the position of the cursor hot spot.

Value	Location of hot spot
HTBORDER	In the border of a window that does not have a sizing border.
HTBOTTOM	In the lower-horizontal border of a resizable window (the user can click the mouse to resize the window vertically).
HTBOTTOMLEFT	In the lower-left corner of a border of a resizable window (the user can click the mouse to resize the window diagonally).
HTBOTTOMRIGHT	In the lower-right corner of a border of a resizable window (the user can click the mouse to resize the window diagonally).
HTCAPTION	In a title bar.
HTCLIENT	In a client area.
HTCLOSE	In a Close button.
HTERROR	On the screen background or on a dividing line between windows (same as HTNOWHERE, except that the DefWindowProc function produces a system beep to indicate an error).
HTGROWBOX	In a size box (same as HTSIZE).
HTHELP	In a Help button.
HTHSCROLL	In a horizontal scroll bar.
HTLEFT	In the left border of a resizable window (the user can click the mouse to resize the window horizontally).
HTMENU	In a menu.
HTMAXBUTTON	In a Maximize button.
HTMINBUTTON	In a Minimize button.
HTNOWHERE	On the screen background or on a dividing line between windows.
HTREDUCE	In a Minimize button.
HTRIGHT	In the right border of a resizable window (the user can click the mouse to resize the window horizontally).
HTSIZE	In a size box (same as HTGROWBOX).
HTSYSMENU	In a window menu or in a Close button in a child window.
HTTOP	In the upper-horizontal border of a window.
HTTOPLEFT	In the upper-left corner of a window border.
HTTOPRIGHT	In the upper-right corner of a window border.
HTTRANSPARENT	In a window currently covered by another window in the same thread (the message will be sent to underlying windows in the same thread until one of them returns a code that is not HTTRANSPARENT).
HTVSCROLL	In the vertical scroll bar.
HTZOOM	In a Maximize button.

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.

Windows Vista: When creating custom frames that include the standard caption buttons, this message should first be passed to the DwmDefWindowProc function. This enables the Desktop Window Manager (DWM) to provide hit-testing for the captions buttons. If DwmDefWindowProc does not handle the message, further processing of WM_NCHITTEST may be needed.

Notification Requirements

Minimum DLL Version	None
Header	Declared in Winuser.h, include Windows.h
Minimum operating systems	Windows 95, Windows NT 3.1

See Also

Mouse Input Overview, DefWindowProc, GET_X_LPARAM, GET_Y_LPARAM, MAKEPOINTS, POINTS