SDL_Init() simply forwards to calling SDL_InitSubSystem(). Therefore, the two may be used
interchangeably. Though for readability of your code SDL_InitSubSystem() might be preferred.
The file I/O (for example: SDL_IOFromFile) and threading (SDL_CreateThread) subsystems are initialized by
default. Message boxes (SDL_ShowSimpleMessageBox) also attempt to work without initializing the video
subsystem, in hopes of being useful in showing an error dialog when SDL_Init fails. You must specifically
initialize other subsystems if you use them in your application.
Logging (such as SDL_Log) works without initialization, too.
flags may be any of the following OR'd together:
• SDL_INIT_AUDIO: audio subsystem; automatically initializes the events subsystem
• SDL_INIT_VIDEO: video subsystem; automatically initializes the events subsystem, should be initialized
on the main thread.
• SDL_INIT_JOYSTICK: joystick subsystem; automatically initializes the events subsystem
• SDL_INIT_HAPTIC: haptic (force feedback) subsystem
• SDL_INIT_GAMEPAD: gamepad subsystem; automatically initializes the joystick subsystem
• SDL_INIT_EVENTS: events subsystem
• SDL_INIT_SENSOR: sensor subsystem; automatically initializes the events subsystem
• SDL_INIT_CAMERA: camera subsystem; automatically initializes the events subsystem
Subsystem initialization is ref-counted, you must call SDL_QuitSubSystem() for each SDL_InitSubSystem()
to correctly shutdown a subsystem manually (or call SDL_Quit() to force shutdown). If a subsystem is
already loaded then this call will increase the ref-count and return.
Consider reporting some basic metadata about your application before calling SDL_Init, using either
SDL_SetAppMetadata() or SDL_SetAppMetadataProperty().