The WM_GETMINMAXINFO message is sent to a window when the size or position of the window is about to change. An application can use this message to override the window’s default maximized size and position, or its default minimum or maximum tracking size.
WM_GETMINMAXINFO lpmmi = (LPMINMAXINFO) lParam; // address of structure
If an application processes this message, it should return zero.
The maximum tracking size is the largest window size that can be produced by using the borders to size the window. The minimum tracking size is the smallest window size that can be produced by using the borders to size the window.