[TUTORIAL] How to use game states in c++

[lokiare1]

What are game states? game states are the different phases a game can be put in. Examples are the splash screen, menu, game play, and credits or ending of a game. There is a simple and easy way to implement game states within a game.

First you must create a game state super class for other states to inherit from:

// Class declaration in GameState.h
class GameState
{
     // Constructor
     GameState();

     // Before render (the = 0 means it must be overridden in a derived class
     virtual bool BeforeRender() = 0;

     // After render
     virtual bool AfterRender() = 0;

     // Destructor (virtual to force the use of derived classes functions when calling from a GameState * object)
     virtual bool ~GameState();
};
// Class implementation in GameState.cpp
GameState::GameState()
{
     // Set up your variables and stuff here
}

GameState::~GameState()
{
     // Delete pointers and let go of assets here
}

After you have this class you make each of your derived classes which must include the functions BeforeRender and AfterRender implemented in them.

Your main code will look like this:

// where play state is an inherited class from GameState
#include <stack>
#include "PlayState.h"

// For <stack>
using namespace std;

// Our stack of states (if you don't understand this look up templates)
stack<GameState *> stateStack;

main()
{
     // Create a new play state
     PlayState * play = new PlayState();

     // Add the play state to the stack
     stateStack.push(play);

     // Create and add another play state
     PlayState * play2 = new PlayState();
     stateStack.push(play2);

     // Main game loop
     bool end = false;

     // Loop until we set end to true
     while (end == false)
     {
          // Get our top state, and do the before render
          stateStack.top()->BeforeRender();

          // Do whatever rendering your render engine uses
          Render();

          // Get our top state, and do the after render stuff
          stateStack.top()->AfterRender();
     }
}

That is how you use game states. You can have as many states as your memory allows, and you can pretty much do whatever you want different in each state.