Is it possible to use select(2) to watch for SDL text input events?

Question

We have to program a server and a client using event-driven programming - we use select(2) to read from stdin and sockets. I'm making an interface for the client using the SDL2 and SDL2_TTF libraries. The problem is I don't know how to make select(2) work for SDL text input events, so I cannot connect the client to my interface. How should I do that? Is there a file descriptor I can use to watch my input on the SDL window?

I forgot to mention: we have to use select(2)

Sure! The _while_ I use for the client is here https://codepaste.net/ukxfdt — liara, Nov 06 '17 at 22:18

genpfault · Answer 1 · 2017-11-07T16:29:01.603

Is there a file descriptor I can use to watch my input on the SDL window?

Nope. Best you can do is get some platform-specific window handles via SDL_GetWindowWMInfo() & the SDL_SysWMinfo struct.

You might be able to use ConnectionNumber() on x11.display and select(2) on it but that's really X11-specific.

How should I do that?

Have the main/GUI/SDL thread send messages to your networking thread via write(2) on a local socket which the networking thread also select(2)s on. For network thread to main thread communication you can use SDL_PushEvent() with a custom event to wake up SDL_WaitEvent().

score 0 · Answer 2 · answered Nov 06 '17 at 21:39

SDL has a polling based event handling so you'll basically want a loop as in

while (!quitting) {
 pollEvents();
 drawEverything();
 delayForFPS();
}

How to poll for events and how to manage text input events is explained everywhere on SDL tutorials as in this one or here, but basically it's something like:

SDL_Event event;
if (SDL_PollEvent(&event)) {
  if (event.type == SDL_TEXTINPUT) {
   std::string text = event.text.text;
  }
}

So there is no stdin or select involved at all.

Mind that since you need networking features the above loop may include pollForPendingPackets() and dispatchPackets() phases which take this into account.

A good approach would be to have the networking thread receive all packets and queue them in a buffer which is then handled by the SDL thread.

I forgot to mention that the assignment specifically tell us to use select from sys/types.h, so I have to use it — liara, Nov 06 '17 at 21:46
indeed you will use `select` to manage sockets, not to handle `stdin`. — Jack, Nov 06 '17 at 21:48

Is it possible to use select(2) to watch for SDL text input events?

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