This lets apps optionally have a handful of callbacks for their entry points instead of a single main function. If used, the actual main/SDL_main/whatever entry point will be implemented in the single-header library SDL_main.h and the app will implement four separate functions:
First:
int SDL_AppInit(int argc, char **argv);
This will be called once before anything else. argc/argv work like they always do. If this returns 0, the app runs. If it returns < 0, the app calls SDL_AppQuit and terminates with an exit code that reports an error to the platform. If it returns > 0, the app calls SDL_AppQuit and terminates with an exit code that reports success to the platform. This function should not go into an infinite mainloop; it should do any one-time startup it requires and then return.
Then:
int SDL_AppIterate(void);
This is called over and over, possibly at the refresh rate of the display or some other metric that the platform dictates. This is where the heart of your app runs. It should return as quickly as reasonably possible, but it's not a "run one memcpy and that's all the time you have" sort of thing. The app should do any game updates, and render a frame of video. If it returns < 0, SDL will call SDL_AppQuit and terminate the process with an exit code that reports an error to the platform. If it returns > 0, the app calls SDL_AppQuit and terminates with an exit code that reports success to the platform. If it returns 0, then SDL_AppIterate will be called again at some regular frequency. The platform may choose to run this more or less (perhaps less in the background, etc), or it might just call this function in a loop as fast as possible. You do not check the event queue in this function (SDL_AppEvent exists for that).
Next:
int SDL_AppEvent(const SDL_Event *event);
This will be called once for each event pushed into the SDL queue. This may be called from any thread, and possibly in parallel to SDL_AppIterate. The fields in event do not need to be free'd (as you would normally need to do for SDL_EVENT_DROP_FILE, etc), and your app should not call SDL_PollEvent, SDL_PumpEvent, etc, as SDL will manage this for you. Return values are the same as from SDL_AppIterate(), so you can terminate in response to SDL_EVENT_QUIT, etc.
Finally:
void SDL_AppQuit(void);
This is called once before terminating the app--assuming the app isn't being forcibly killed or crashed--as a last chance to clean up. After this returns, SDL will call SDL_Quit so the app doesn't have to (but it's safe for the app to call it, too). Process termination proceeds as if the app returned normally from main(), so atexit handles will run, if your platform supports that.
The app does not implement SDL_main if using this. To turn this on, define SDL_MAIN_USE_CALLBACKS before including SDL_main.h. Defines like SDL_MAIN_HANDLED and SDL_MAIN_NOIMPL are also respected for callbacks, if the app wants to do some sort of magic main implementation thing.
In theory, on most platforms these can be implemented in the app itself, but this saves some #ifdefs in the app and lets everyone struggle less against some platforms, and might be more efficient in the long run, too.
On some platforms, it's possible this is the only reasonable way to go, but we haven't actually hit one that 100% requires it yet (but we will, if we want to write a RetroArch backend, for example).
Using the callback entry points works on every platform, because on platforms that don't require them, we can fake them with a simple loop in an internal implementation of the usual SDL_main.
The primary way we expect people to write SDL apps is with SDL_main, and this is not intended to replace it. If the app chooses to use this, it just removes some platform-specific details they might have to otherwise manage, and maybe removes a barrier to entry on some future platform.
Fixes#6785.
Reference PR #8247.
These are test programs for the SDL library:
checkkeys Watch the key events to check the keyboard
loopwave Audio test -- loop playing a WAV file
testsurround Audio test -- play test tone on each audio channel
testaudioinfo Lists audio device capabilities
testerror Tests multi-threaded error handling
testfile Tests RWops layer
testgl A very simple example of using OpenGL with SDL
testiconv Tests international string conversion
testkeys List the available keyboard keys
testloadso Tests the loadable library layer
testlocale Test Locale API
testlock Hacked up test of multi-threading and locking
testmouse Tests mouse coordinates
testmultiaudio Tests using several audio devices
testoverlay Tests the overlay flickering/scaling during playback.
testplatform Tests types, endianness and cpu capabilities
testsem Tests SDL's semaphore implementation
testshape Tests shaped windows
testsprite Example of fast sprite movement on the screen
testthread Hacked up test of multi-threading
testtimer Test the timer facilities
testver Check the version and dynamic loading and endianness
testwm Test window manager -- title, icon, events
torturethread Simple test for thread creation/destruction
gamepadmap Useful to generate Game Controller API compatible maps
This directory contains sample.wav, which is a sample from Will Provost's
song, The Living Proof:
From the album The Living Proof
Publisher: 5 Guys Named Will
Copyright 1996 Will Provost
You can get a copy of the full song (and album!) from iTunes...
https://itunes.apple.com/us/album/the-living-proof/id4153978
or Amazon...
http://www.amazon.com/The-Living-Proof-Will-Provost/dp/B00004R8RH
Thanks to Will for permitting us to distribute this sample with SDL!
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