This disables the maximize button (you need Windows.h included for these functions and it's best to do it in some separate cpp file because Windows.h has tons of weird crap defined in it). You should take a better look on MSDN too because most of simple things are simple to do with WinApi.
auto win = sfmlwindow.getSystemHandle();
auto style = GetWindowLong(win, GWL_STYLE);
SetWindowLong(win, GWL_STYLE, style & ~WS_MAXIMIZEBOX);
Because SFML not have window maximize Event >> https://en.sfml-dev.org/forums/index.php?topic=8830.0
And I can't detect its manual resized or from Max button.
FullScreen with proportions I already have.
And Maximize not work for my logic Render, because my View is Original - not 1 to 1.
I can improve Maximize to my render logic only if detect exact sizes of visible Desktop area without Taskbar.
Maybe its help me >> http://forum.lazarus-ide.org/index.php/topic,9858.msg53098.html#msg53098
Or need simply check from window handle from WinApi Maximize status.
auto w_Hnd = win.getSystemHandle();
WINDOWPLACEMENT w_Plc;
GetWindowPlacement(w_Hnd, &w_Plc);
if (w_Plc.showCmd == SW_SHOWMAXIMIZED)
{
// here do proportion adjustment
}