[SDL] Re: Events

[Rainer Deyke]

"David Hedbor" <newsgroups at animearchive.org> wrote in message
news:m3n1989h09.fsf at stellar.home.hedbor.org...
> In any case, I have a very nice event system in my opinion. Basically,
> you create a classed derived from EventHandler (documented at
> http://sdlmm.sourceforge.net/class_SDLmm__EventHandler.html). Each
> type of callback has one or more potential handlers. Here's a simple
> example of it's use:

Sorry, but that system is simply awful.  Consider the following code:

void wait_for_key() {
  SDL_Event e;
  while (SDL_PollEvent(&e)) {
    if (e.type == SDL_KEYDOWN) {
      return;
    }
  }
}

That's eight lines of code.  Then consider what I'd have to do in your
system:

class WaitForKeyEventHandler : public SDLmm::EventHandler {
public:
  bool done;
  WaitForKeyEventHandler() : done(false) {}
  bool HandleKeyPressEvent(SDL_keysym&)
  {
    this->done = true;
    return true;
  }
};

void wait_for_key_press()
{
  WaitForKeyEventHandler ev;
  while (!ev.done) {
    SDLmm::Event::HandleEvent(ev);
  }
}

That's 18 lines of code: more than twice the original.  It is also more
complicated and less readable.  Now consider that there may be hundreds of
places in a program where events are handled differently (think dialogs).
Each of these would see a similar increase in size and complexity.  True,
you can use inheritance to factor out common functionality - but this
provides no advantage over factoring through free functions.


--
Rainer Deyke (root at rainerdeyke.com)
Shareware computer games           -           http://rainerdeyke.com
"In ihren Reihen zu stehen heisst unter Feinden zu kaempfen" - Abigor