An application sends this message to retrieve the zero-based index of the item nearest the specified point in a list box.
LB_ITEMFROMPOINT wParam = 0; // not used, must be zero lParam = (LPARAM) MAKELPARAM(xPos, yPos); // coordinates of point
The return value contains the index of the nearest item in the low-order word. The high-order word is zero if the specified point is in the client area of the list box, or one if it is outside the client area.