This sets the window size for platforms that support it, such as Windows and Mac. This will not affect mobile devices. In fullscreen mode the width and height will be ignored and the desktop resolution will be used. By default the window size will be adjusted so it always fits on screen, including making room for the taskbar on Windows. This means that your final window size may be slightly smaller than your chosen size. You can override this by setting the allowOverSized parameter to 1, which will remove all bounds checks and allow you to create windows larger than the current screen. When the fullscreen parameter is set to 1 then the allowOverSized parameter has no effect.
SetWindowSize( width, height, fullscreen, allowOverSized )
SetWindowSize( width, height, fullscreen )