Invalidating the non client area
Prepare for changing positions of multiple child windows.
This method should be called before changing positions of multiple child windows to reduce flicker and, in MSW case, even avoid display corruption in some cases.
In particular, this means that you must release the mouse as many times as you capture it, unless the window receives the Note This methods provides for a way to centre top level windows over their parents instead of the entire screen.
If there is no parent or if the window is not a top level window, then behaviour is the same as return if this window had client area of given size.
Components with Default Coord value are left unchanged.
Notice that the best size returned by this function is cached internally, so if anything that results in the best size changing (e.g.
change to the control contents) happens, you need to call rather than this method itself as you need to explicitly account for the window borders size if you do the latter.