SDL Game Development

Each platform has its own way of creating and displaying windows and graphics, handling user input, and accessing any low-level hardware; each one with its own intricacies and syntax. SDL provides a uniform way of accessing these platform-specific features. This uniformity leads to more time spent tweaking your game rather than worrying about how a specific platform allows you to render or get user input, and so on. Game programming can be quite difficult, and having a library such as SDL can get your game up and running relatively quickly.

The ability to write a game on Windows and then go on to compile it on OSX or Linux with little to no changes in the code is extremely powerful and perfect for developers who want to target as many platforms as possible; SDL makes this kind of cross-platform development a breeze. While SDL is extremely effective for cross-platform development, it is also an excellent choice for creating a game with just one platform in mind, due to its ease of use and abundance of features.

SDL has a large user base and is being actively updated and maintained. There is also a responsive community along with a helpful mailing list. Documentation for SDL 2.0 is up-to-date and constantly maintained. Visiting the SDL website, libsdl.org, offers up lots of articles and information with links to the documentation, mailing list, and forums.

Overall, SDL offers a great place to start with game development, allowing you to focus on the game itself and ignore which platform you are developing for, until it is completely necessary. Now, with SDL 2.0 and the new features it brings to the table, SDL has become an even more capable library for game development using C++.

This book will cover setting up SDL 2.0 in Microsoft's Visual C++ Express 2010 IDE. This IDE was chosen as it is available for free online, and is a widely used development environment within the games industry. The application is available at https://www.microsoft.com/visualstudio/en-gb/express. Once the IDE has been installed we can go ahead and download SDL 2.0. If you are not using Windows to develop games, then these instructions can be altered to suit your IDE of choice using its specific steps to link libraries and include files.

SDL 2.0 is still in development so there are no official releases as yet. The library can be retrieved in two different ways:

Both of these options are available at http://www.libsdl.org/hg.php.

Building SDL 2.0 on Windows also requires the latest DirectX SDK, which is available at http://www.microsoft.com/en-gb/download/details.aspx?id=6812, so make sure this is installed first.

We now have an empty project, which links to the SDL library, so it is time to start our SDL development. Click on Source Files and use the keyboard shortcut Ctrl + Shift + A to add a new item. Create a C++ file called main.cpp. After creating this file, copy the following code into the source file:

#include<SDL.h>

SDL_Window* g_pWindow = 0;
SDL_Renderer* g_pRenderer = 0;

int main(int argc, char* args[])
{
  // initialize SDL
  if(SDL_Init(SDL_INIT_EVERYTHING) >= 0)
  {
    // if succeeded create our window
    g_pWindow = SDL_CreateWindow("Chapter 1: Setting up SDL", 
    SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
    640, 480, 
    SDL_WINDOW_SHOWN);

    // if the window creation succeeded create our renderer
    if(g_pWindow != 0)
    {
      g_pRenderer = SDL_CreateRenderer(g_pWindow, -1, 0);
    }
  }
  else
  {
    return 1; // sdl could not initialize
  }

  // everything succeeded lets draw the window

  // set to black // This function expects Red, Green, Blue and 
  //  Alpha as color values
  SDL_SetRenderDrawColor(g_pRenderer, 0, 0, 0, 255);

  // clear the window to black
  SDL_RenderClear(g_pRenderer);

  // show the window
  SDL_RenderPresent(g_pRenderer);

  // set a delay before quitting
  SDL_Delay(5000);

  // clean up SDL
  SDL_Quit();

  return 0;
}

We can now attempt to build our first SDL application. Right-click on the project and choose Build. There will be an error about the SDL.dll file not being found:

The attempted build should have created a Debug or Release folder within the project directory (usually located in your Documents folder under visual studio and projects). This folder contains the .exe file from our attempted build; we need to add the SDL.dll file to this folder. The SDL.dll file is located at C:\SDL2\VisualC\SDL\Win32 (or x64)\Release\SDL.dll l). When you want to distribute your game to another computer, you will have to share this file as well as the executable. After you have added the SDL.dll file to the executable folder, the project will now compile and show an SDL window; wait for 5 seconds and then close.

SDL_Init(SDL_INIT_AUDIO | SDL_INIT_VIDEO);

if(SDL_WasInit(SDL_INIT_VIDEO) != 0)
{
  cout << "video was initialized";
}

Outside the design and gameplay of a game, the underlying mechanics are essentially the interaction of various subsystems such as graphics, game logic, and user input. The graphics subsystem should not know how the game logic is implemented or vice versa. We can think of the structure of a game as follows:

Once the game is initialized, it then goes into a loop of checking for user input, updating any values based on the game physics, before rendering to the screen. Once the user chooses to exit, the loop is broken and the game moves onto cleaning everything up and exiting. This is the basic scaffold for a game and it is what will be used in this book.

We will be building a reusable framework that will take all of the legwork out of creating a game in SDL 2.0. When it comes to boilerplate code and setup code, we really only want to write it once and then reuse it within new projects. The same can be done with drawing code, event handling, map loading, game states, and anything else that all games may require. We will start by breaking up the Hello SDL 2.0 example into separate parts. This will help us to start thinking about how code can be broken into reusable standalone chunks rather than packing everything into one large file.

bool g_bRunning = false; // this will create a loop

void init(){}
void render(){}
void update(){}
void handleEvents(){}
void clean(){}

bool g_bRunning = true;

int main()
{
  init();

  while(g_bRunning)
  {
    handleEvents();
    update();
    render();
  }

  clean();
}

So, now that we have an idea of what makes up a game, we can separate the functions into their own class by following these steps:

Looking back at the first part of this chapter (where we created an SDL window), we know that we need a pointer to an SDL_Window object that is set when calling SDL_CreateWindow, and a pointer to an SDL_Renderer object that is created by passing our window into SDL_CreateRenderer. The init function can be extended to use the same parameters as in the initial sample as well. This function will now return a Boolean value so that we can check whether SDL is initialized correctly:

bool init(const char* title, int xpos, int ypos, int width, int height, int flags);

We can now create a new implementation Game.cpp file in the project so that we can create the definitions for these functions. We can take the code from the Hello SDL section and add it to the functions in our new Game class.

Open up Game.cpp and we can begin adding some functionality:

So we have moved the Hello SDL 2.0 code from the main.cpp file into a class called Game. We have freed up the main.cpp file to handle only the Game class; it knows nothing about SDL or how the Game class is implemented. Let's add one more thing to the class to allow us to close the application the regular way:

void Game::handleEvents()
{
  SDL_Event event;
  if(SDL_PollEvent(&event))
  {
    switch (event.type)
    {
      case SDL_QUIT:
        m_bRunning = false;
      break;

      default:
      break;
    }
  }
}

We will cover event handling in more detail in a forthcoming chapter. What this function now does is check if there is an event to handle, and if so, check if it is an SDL_QUIT event (by clicking on the cross to close a window). If the event is SDL_QUIT, we set the Game class' m_bRunning member variable to false. The act of setting this variable to false makes the main loop stop and the application move onto cleaning up and then exiting:

void Game::clean()
{
  std::cout << "cleaning game\n";
  SDL_DestroyWindow(m_pWindow);
  SDL_DestroyRenderer(m_pRenderer);
  SDL_Quit();
}

The clean() function destroys the window and renderer and then calls the SDL_Quit() function, closing all the initialized SDL subsystems.

bool init(const char* title, int xpos, int ypos, int width, int height, int flags);

// init the window
m_pWindow = SDL_CreateWindow(title, xpos, ypos, width, height, flags);

g_game->init("Chapter 1", 100, 100, 640, 580, SDL_WINDOW_FULLSCREEN))

if(g_game->init("Chapter 1", 100, 100, 640, 480, true))

A lot of ground has been covered in this chapter. We learned what SDL is and why it is a great tool for game development. We looked at the overall structure of a game and how it can be broken into individual parts, and we started to develop the skeleton of our framework by creating a Game class that can be used to initialize SDL and render things to the screen. We also had a small look at how SDL handles events by listening for a quit event to close our application. In the next chapter we will look at drawing in SDL and building the SDL_image extension.