[SDL] Re: Events

[Jone Marius Vignes]

On Monday 23 April 2001 18:21, you wrote:
> "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.
>
>

Granted you want an object to do something on a KeyDownEvent, here's how 
you'd do it in KGB:

class LetsCallItButton:public KGB_KeydownHandler{
	public:
		LetsCallItButton():KGB_KeyDownHandler(){
			game->registerKeydownHandler(this);
		}
	
	void handleKeydownEvent(SDLKey key){
		do_stuff_here();
	}
}

...to show another way of doing it in an object-oriented manner. You just 
make the object responding to an event a subclass of the proper eventhandler, 
and implement handle*Event(*).

BLiP!