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 posted 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 window |
| HTBOTTOMLEFT | In the lower-left corner of a window border |
| HTBOTTOMRIGHT | In the lower-right corner of a window border |
| HTCAPTION | In a title bar |
| HTCLIENT | In a client area |
| 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) |
| HTHSCROLL | In a horizontal scroll bar |
| HTLEFT | In the left border of a window |
| HTMENU | In a menu |
| HTNOWHERE | On the screen background or on a dividing line between windows |
| HTREDUCE | In a Minimize button |
| HTRIGHT | In the right border of a window |
| 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 |
| 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.
See Also