What do the SDL_Init, IMG_Init and TTF_Init functions do?

These functions are used to initialize the SDL library and its associated sub-systems. Let's look at each one:

SDL_Init(Uint32 flags)

This function initializes the SDL library. It must be called before using most other SDL functions. The flags parameter specifies which SDL subsystems to initialize. In the example code:

1SDL_Init(SDL_INIT_VIDEO);

This initializes the video subsystem, which is required for creating windows, rendering graphics, handling input events, etc. Other possible flags include SDL_INIT_AUDIO, SDL_INIT_TIMER, etc.

IMG_Init(int flags)

This function initializes the SDL_image library, which is an extension library that allows you to load various image formats like PNG, JPG, etc. The flags parameter specifies which image formats to support. In the example code:

1IMG_Init(IMG_INIT_PNG);

This initializes support for PNG images. You can OR multiple flags together to support multiple formats, e.g., IMG_Init(IMG_INIT_PNG | IMG_INIT_JPG).

TTF_Init()

This function initializes the SDL_ttf library, which is an extension library for rendering TrueType fonts. Unlike SDL_Init and IMG_Init, it doesn't take any flags - it simply initializes the library.

All of these functions return 0 on success, or a negative error code on failure. It's good practice to check the return value and handle any errors, e.g.:

1if (SDL_Init(SDL_INIT_VIDEO) != 0) {
2  std::cout << "SDL_Init Error: "
3    << SDL_GetError() << std::endl;
4  return 1;
5}

It's important to call these initialization functions before using any functionality from the respective libraries. For SDL and SDL_image, you also need to call SDL_Quit() and IMG_Quit() before your program exits to clean up resources.

So in summary, these init functions set up the SDL libraries, allowing you to then use their features in your code. They're a crucial first step in any SDL application.