SFML Template to start with your game

07-05-2020

If you have setup SFML with the tutorial that I wrote, the example is easy but is not very useful if you want to create more complex games.

In this post, I going to show you how I create a simple Game class to have more control about the game loop, the user input and the frame rate.

First, you need to create a Game.h and Game.cpp files. In your Game.h write this code

#ifndef GAME_H
#define GAME_H

#include <SFML/Graphics.hpp>

class Game
{
public:
    Game();
    void Run();

private:
    void processEvents();
    void update(sf::Time deltaTime);
    void render();
    void handlePlayerInput(sf::Keyboard::Key key, bool isPressed);

    sf::RenderWindow mWindow;

    static const sf::Time TimePerFrame;
};

#endif //GAME_H

This is the header of our Game class, as you can see, we have only a constructor and one public method run, all other methods are private to Game.

We have one method for process the SFML events and one for the player input. The update method take a delta time which is going to help us with the frame rate and with other stuffs.

And we have the render method, that is going to draw our game.

We need a RenderWindow to render our window 😛 and finally a const to help us with the frame rate.

Now, in the Game.cpp file, write the next code

//
// Created by Giovanni Cortes on 07/05/20.
//

#include "Game.h"

const sf::Time Game::TimePerFrame = sf::seconds(1.f/60.f);

Game::Game()
: mWindow(sf::VideoMode(640, 480), "Your Awesome Game!")
{
}

void Game::Run()
{
    sf::Clock clock;
    sf::Time timeSinceLastUpdate = sf::Time::Zero;

    while (mWindow.isOpen())
    {
        timeSinceLastUpdate += clock.restart();
        while (timeSinceLastUpdate > TimePerFrame)
        {
            timeSinceLastUpdate -= TimePerFrame;
            processEvents();
            update(TimePerFrame);
        }
        render();
    }
}

void Game::processEvents()
{
    sf::Event event{};

    while (mWindow.pollEvent(event))
    {
        switch (event.type)
        {
            case sf::Event::KeyPressed:
                handlePlayerInput(event.key.code, true);
                break;
            case sf::Event::KeyReleased:
                handlePlayerInput(event.key.code, false);
                break;
            case sf::Event::Closed:
                mWindow.close();
                break;
            default:
                break;
        }

    }
}

void Game::update(sf::Time deltaTime)
{
    // TODO: Update your objects here
    // Example: mWindow.draw(mPlayer);
}

void Game::render()
{
    mWindow.clear();

    // TODO: Draw your objects here

    mWindow.display();
}

void Game::handlePlayerInput(sf::Keyboard::Key key, bool isPressed)
{
    // TODO: Key events for your game
    // Example:
    // if (key == sf::Keyboard::W)
    // {
    //     mIsMovingUp = isPressed;
    // }
}

The most important method, is the run method. We have locked our game loop to 60 frames per second thanks to line

const sf::Time TimePerFrame = sf::seconds(1.f/60.f);

SFML has a setFrameLimit() method, but I prefer use mine for control and for learning.

The remains methods are self explanatory but if you have any doubt, you can write me to explain more in detail.

Running the game loop

#include "Game.h"

int main()
{
    Game game;
    game.Run();
    return 0;
}

As you can see, the code is very simple, we create a Game instance and run our game loop. If you run this, you are going to see this window

running_SFML

Now, you can extend your game and have a better control of your game loop.