WM_NCHITTEST

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. 

WM_NCHITTEST 
xPos = LOWORD(lParam);  // horizontal position of cursor 
yPos = HIWORD(lParam);  // vertical position of cursor

Parameters

xPos
Value of the low-order word of lParam. Specifies the x-coordinate of the cursor. The coordinate is relative to the upper-left corner of the screen.
yPos
Value of the high-order word of lParam. Specifies the y-coordinate of the cursor. The coordinate is relative to the upper-left corner of the screen.

Return Values

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 Maximize button
HTMINBUTTON In 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 System 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

An application can use the MAKEPOINTS macro to convert the lParam parameter to a POINTS structure.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Unsupported.
  Header: Declared in winuser.h.

See Also

Mouse Input Overview, Mouse Input Messages, DefWindowProc, MAKEPOINTS, POINTS