Integrate SDL into GLib mainloop

I'm planning a small Vala game project with SDL and I wonder how to integrate SDL properly into the GLib mainloop. The last time I did something with Vala and SDL I used the standard SDL event loop, but honestly, it's a heap of crap and it breaks the whole nice Vala or rather GLib signal system.

I found an integration for Cogl and I'm looking for the same thing just with SDL.

GLib sources are composed of three callbacks:

• one to check if the source is ready before polling (and avoid a poll call)
• one to check if the source is still ready after polling
• one to dispatch the attached callback

You could have a source checking and dispatching events fairly simply.

public delegate bool SDLSourceFunc (SDL.Event event);

public class SDLSource : Source 
{
    public SDL.Event event;

    public bool prepare (out uint timeout) 
    {
        timeout = 0;
        return true;
    }

    public bool check ()
    {
        return SDL.Event.poll (out event) > 0;
    }

    public bool dispatch (SourceFunc callback) 
    {
        return ((SDLSourceFunc) callback) (event);
    }

    public void add_callback (SDLSourceFunc callback)
    {
        base.add_callback ((SourceFunc) callback);
    }
}

Then, you would loop with Source.CONTINUE:

var source = new SDLSource ();

source.add_callback ((event) => {
    // handle event here
    return Source.CONTINUE;
});

source.attach (MainContext.@default ());

This is very basic: your source could filter specific events with a SDL.EventMask and SDL.peep. It's also more efficient to dispatch multiple events for a single source and attach related file descriptors.

If you use some async code, you can wakeup the coroutine directly from a Source dispatch:

public async void next_event_async () 
{
    var source = new SDLSource ();
    source.attach (MainContext.@default ());
    source.add_callback (next_event_async.callback);
    yield;
    return source.event;
}