optional event-driven callback-main

[expikr]

SDL really offer quite a complete package for general app development, however one dealbreaker is the busy-wait polling of SDL_WaitEvents() making it unsuited for background apps.

With the addition of callback-based main, I think there is an opportunity here to add the ability for making truly event-driven blocking main loops.

Some ideas for how to expose this functionality as an interface:

• Idea 1: add a new SDL_APP_WAITEVENT entry to the SDL_AppResult enum that directs control flow to a blocking event wait.

  • the developer can return this from SDL_AppEvent() to skip calling SDL_AppIterate() for that iteration.
  • the developer can return this from SDL_AppIterate() to choose to block until next event instead of going straight to event pumping

• Idea 2: add a hint or function call that globally switches between poll-based and wait-based event loop, then SDL_AppIterate() is called only on a timer message.

• Idea 3: dynamically detect whether or not SDL_AppIterate() is defined, use wait-based event loop when absent and poll-based event loop when present.

[namandixit]

If this is added and idea 1 (new return value) is used, then another addition can be SDL_APP_SKIPEVENTS that can be used to force a call to SDL_AppIterate even if the event queue is not emptied. The events left in the queue can be emptied after SDL_AppIterate returns, unless the user returns SDL_APP_SKIPEVENTS again.