I have problem adjusting the size of the screen, using the ScalableGame class from Slick2D library.

So, what I want to achieve, whenever I change display size, background should adjust to screen size, and objects (images, grahpic shapes) should fit (scale).

Alright, so this is how state looks by default. I can change screen size, but images and graphic shapes does not

appGameContainer = new AppGameContainer(
     new ScalableGame(new AppStateController(), Settings.video.getWidth(), Settings.video.getHeight(), true)
);
appGameContainer.setDisplayMode(Settings.video.getWidth(), Settings.video.getHeight(), Settings.video.isFullScreen());
appGameContainer.start();

If I assign to width/height +100, ScalableGame constructor:

appGameContainer = new AppGameContainer(
     new ScalableGame(new AppStateController(), Settings.video.getWidth() + 100, Settings.video.getHeight() + 100, true)
);
appGameContainer.setDisplayMode(Settings.video.getWidth(), Settings.video.getHeight(), Settings.video.isFullScreen());
appGameContainer.start();

If I assign to width/height +100, to display:

appGameContainer = new AppGameContainer(
     new ScalableGame(new AppStateController(), Settings.video.getWidth(), Settings.video.getHeight(), true)
);
appGameContainer.setDisplayMode(Settings.video.getWidth() + 100, Settings.video.getHeight() + 100, Settings.video.isFullScreen());
appGameContainer.start();