The framework calls this member function for the CWnd object that contains the cursor (or the CWnd object that used the SetCapture member function to capture the mouse input) every time the mouse is moved.
This member function is called by the framework to allow your application to handle a Windows message. The parameters passed to your function reflect the parameters received by the framework when the message was received. If you call the base-class implementation of this function, that implementation will use the parameters originally passed with the message and not the parameters you supply to the function.
HTBORDER In the border of a window that does not have a sizing border.
HTBOTTOM In the lower horizontal border of the window.
HTBOTTOMLEFT In the lower-left corner of the window border.
HTBOTTOMRIGHT In the lower-right corner of the window border.
HTCAPTION In a title-bar area.
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 DefWndProc Windows function produces a system beep to indicate an error).
HTGROWBOX In a size box.
HTHELP In a Help button.
HTHSCROLL In the horizontal scroll bar.
HTLEFT In the left border of the window.
HTMAXBUTTON In a Maximize button.
HTMENU In a menu area.
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 the window.
HTSIZE In a size box (same as HTGROWBOX).
HTSYSMENU In a Control menu or in a Close button in a child window.
HTTOP In the upper horizontal border of the window.
HTTOPLEFT In the upper-left corner of the window border.
HTTOPRIGHT In the upper-right corner of the window border.
HTTRANSPARENT In a window currently covered by another window.
HTVSCROLL In the vertical scroll bar.
HTZOOM In a Maximize button.