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The core of State management, the GUI and the Entity system

4: Adsense

Hello GameDev,

Arhim here with the second entry for this journal. Continuing from the last time I will write about other cores needed for the game.

The StateManager is a class that will be responsible for, as the name suggests, managing different states. We will first define a class IState which we will be extending and will provide us with a common interface for states. All states should have a way of updating, drawing and handling events. Also, to make things easier for state managing we will define two additional variables: family and ID. The family variable will store the common type of the state (GameState, MainMenuState...) and the ID will store the specific name of the object as strings.

Core of IState should look like this:
class IState
		IState(std::string mID = ""); // constructor will accept the unique ID

		virtual void update(double k); // the difference in time from the last update
		virtual void draw();

                virtual void handleEvents(const sf::Event &event); // we handle the needed SFML events

                std::string family;
                std::string ID;

                bool isDrawing;   // needed for the StateManager
                bool isUpdating;

This class should provide us with the basic interface we will need for the states.

Coming back to the StateManager, we will store States as IState pointers in a vector and we will implement some basic functions for adding, removing and switching to states (here the variables isDrawing and isUpdating will help out).

The .h file:
class StateManager

                void update(double k);
                void draw();
                void addState(IState* state);
                void removeState(std::string ID);

                void switchToState(std::string ID);

                void handleEvents(const sf::Event &event);


                std::vector<IState*> states;
For now only the switchToState function is needed which sets the updating and drawing flags to true. This should leave room for later making states draw over each other while only one state (or more) get updated.

Coming up with a nice way for doing the GUI was pretty tricky and we finally settled for the following approach: we will have a base class called Container that will implement all the low level needs for the different GUI parts. After that, every GUI part will implement its own specific functions.
class Container

        Container( std::string id = "", double x = 0, double y = 0, double width = 0, double height = 0 );
        virtual ~Container();

        virtual void draw();
        virtual void update( double dt );

        void handleEvents( const sf::Event& event );

        virtual bool mouseLeftDown();
        virtual bool mouseLeftUp();
        virtual void mouseMoved( int x, int y );
        virtual bool mouseWheelMoved( int delta );

        virtual bool keyPressed( unsigned int code );
        virtual bool keyReleased( unsigned int code );
        virtual bool textEntered( unsigned int code );

        void addChild( ContainerPt child );
        void setParent( ContainerPt parent );

        void setColor( const sf::Color& col );

        const bool isHovered() const;
        const bool isFocused() const;
        const bool isPressed() const;

        const std::string& getID() const;

        Vec2f getPosition() const; // absolute position

        // extend...
        virtual bool isClicked(){};
        virtual void setValue( std::string ){};
        virtual void setValue( int ){};
        virtual void setDrawing( bool );
        virtual void setSelected( bool selected ) {};
        virtual void addItem( std::string id, std::string value ) {};

        virtual std::string getStringValue() const {};
        virtual int getIntValue() const{};
        virtual bool isSelected() const{};


        bool m_hovered;
        bool m_focused;
        bool m_pressed;

        bool m_drawing;

        double m_top;
        double m_left;
        double m_width;
        double m_height;

        ContainerPt m_parent;
        std::vector< ContainerPt > m_childs;
        std::string m_id;

        sf::Color m_color;
This should give us a nice foundation for making new GUI elements.

Before starting work on the Entity system we read the different resources which can be found on this wiki. I left programming of this system in the hands of my friend and he took the challenge to himself to make it work really fast (for the cost of some space which shouldn't matter because of the scope).

Anyway, the basics of this approach are the following: you have entities that have a set of components, and system which work only on entities that have the required components (you should read the papers, they are really interesting and I can hardly convey this properly). The way we currently have this implemented uses too much magic (to work fast ;) ) and we will have to clean it or rewrite it before using it in our game and posting it here.

For the end I will post a screenshot of what we have for now:

Posted Image

This is just the basic setup. The New Game, Options and Exit buttons are logical, but the Edit button will lead to the EditState where you will be able to edit maps of the terrain. The edit me box is there just for testing purposes.

I hope you had an interesting read. If you have any suggestions where I should go with this series or what I should change feel free to leave a comment. I am open to new ideas.

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