// public class MyGame extends Game {
public class MyGame extends ApplicationAdapter {

    public ExtendViewport viewport;
    public SpriteBatch sb;
    public Texture bg_image;

    // The WIDTH and HEIGHT is to keep a fixed screen ratio of the "playable" part of game
    public static final int WIDTH = 480;
    public static final int HEIGHT = 800;

    @Override
    public void create () {
        viewport = new ExtendViewport(MyGame.WIDTH, MyGame.HEIGHT);
        sb = new SpriteBatch();

        bg_image = new Texture(Gdx.files.internal("green.png"));
    }

    // render part of game
    @Override
    public void render () {
        Gdx.gl.glClearColor(1, 1, 1, 1);

        // another_viewport.apply();
        // sb.setProjectionMatrix(another_viewport.getCamer().combined);

        //sb.begin();
        //blabla
        //sb.end();

        // I have this since I have an additional viewport
        viewport.apply();
        sb.setProjectionMatrix(viewport.getCamera().combined);

        sb.begin();
        sb.draw(bg_image, 0, 0, MyGame.WIDTH, MyGame.HEIGHT);
        sb.end();

    }

    // Called when resizing the screen
    @Override
    public void resize(int width, int height){
        bg_viewport.update(width, height);
        viewport.update(width, height);
    }

}

public class DesktopLauncher {
    public static void main (String[] arg) {
        LwjglApplicationConfiguration config = new LwjglApplicationConfiguration();
        config.title = "My Game";
        // Works perfectly if width and height matches the world width and height
        config.width = 480;

        // It will make extendViewport not perfectly placed in centrum
        // But will still adjust as intended when changing the size of the window
        // on Desktop while being not perfecty placed

        // Additional. It acts as if you have viewport.apply(true);
        // and viewport.update(x, y, true);
        // So your game extends to the right.
        // After that your game adjusts perfectly, but with an unwanted extend..

        //config.width = 680;

        // This seems to only happen when MyGame extends "Game", not "ApplicationAdapter"
        // Also the 0,0 coordinate is at middle of screen when extend "ApplicationAdapter"
        // 0,0 coordinate is at bottom left corner when extends "Game".

        config.height = 800;
        new LwjglApplication(new MyGame(), config);
    }
}