From: Ken Allen <kallen19918@...>
Date: 2007-03-19T05:58:36+09:00
Subject: Re: ruby-sdl: How do you poll events?

ChrisKaelin wrote:
> The code of my raw main loop is below. I'm sure there are better ways
> to poll the event queue. Do you have better ideas?
> Also I'm not sure about the garbage collect thing at the bottom...
>
> loop {
>       offset_x = 0
>       offset_y = 0
>       if event.poll != 0
> 	    case event.type
>   	    when SDL::Event::QUIT
> 		  break
> 		when SDL::Event::KEYDOWN
> 		  case event.keySym
> 			when SDL::Key::ESCAPE
>               break
>             when SDL::Key::LEFT
>               offset_x = -5
>             when SDL::Key::RIGHT
>               offset_x = +5
>             when SDL::Key::DOWN
>               offset_y = +5
>             when SDL::Key::UP
>               offset_y = -5
> 	      end
> 	    end
> 	  end
>
>     before = now
>     now = SDL::getTicks
>     dt = now-before
>    # here comes the rendering finally
>     player.draw(screen)
>     enemies.each{|i| i.draw(screen)}
>     screen.fillRect(0,0,640,480,0)
>     w.to_sdl(screen, offset_x, offset_y)
>     screen.fillRect(0,0,640,480,0)
>     ObjectSpace.garbage_collect
>     screen.flip
>   }
>
>
>
>   
   Here's the main loop from my game engine. You should poll the event 
queue in a loop or you'll only handle one event every iteration of the 
main loop.
 I handle the input by passing the important info from the event on to 
the top element of a stack of input handlers. This means you can easily 
switch control
contexts by pushing/popping handlers. This isn't really perfect though. 
Ideally it wouldn't be method calls directly on the top element, ideally 
the event poller shouldn't
know about the stack and the input handler should allow for allowing 
events to continue down the stack. Errr, this may not really have been 
what you were asking for.
Also I think there's a helper function in sdl that builds a hash of 
keysyms to booleans that stores the keyboard state.
Anyway, I hope this helps you.

    def main_loop
        @running = true
        @last_time = SDL.get_ticks
        while @running
        while event = SDL::Event2.poll
            case event
            when SDL::Event2::Quit
            quit
            when SDL::Event2::KeyDown
            @input.last.key_down( event.sym ) unless @input.empty?
            when SDL::Event2::KeyUp
            @input.last.key_up( event.sym ) unless @input.empty?
            when SDL::Event2::MouseButtonDown
            @input.last.mouse_down( event.button, P[event.x,event.y] )
            when SDL::Event2::MouseButtonUp
            @input.last.mouse_up( event.button, P[event.x,event.y] )
            end
        end
        current_time = SDL.get_ticks
        if current_time - @last_time > GAME_SPEED
            @last_time = current_time
            Core.objects.update current_time
        end
        Core.display.draw
        end
    end