From QB64 Wiki
The _RESIZE function returns -1 when a user has attempted to resize the program window and $RESIZE:ON has allowed it.
- The function returns -1 if a program screen re-size was attempted by the user.
- After the function returns -1, _RESIZEWIDTH and _RESIZEHEIGHT can return the new dimensions in pixels.
- The $RESIZE:ON metacommand must be used so the program is created with a user resizable window.
- QB64 GL programs only. Not available in QB64 SDL versions .954 and older.