The HDM_LAYOUT message retrieves the size and position of a header control within a given rectangle. This message is used to determine the appropriate dimensions for a new header control that is to occupy the given rectangle. You can send this message explicitly or by using the Header_Layout macro.
HDM_LAYOUT wParam = 0; lParam = (LPARAM) (HD_LAYOUT FAR*) playout;
If the operation succeeds, the return value is TRUE.
If the operation fails, the return value is FALSE.