[A5] Non blocking keypressed

[A5] Non blocking keypressed

zelda007

Member #12,303

October 2010

Hi,

I would like to write a function that replaces the old keypressed() in Allegro 4.4 but this function must be non-blocking (because called in the game loop). I have found this link :
https://www.allegro.cc/forums/thread/610536

But it is blocking.

I try this :

bool keyPressed() {
            al_get_keyboard_state(&kbdstate);
            for (unsigned int i=0; i<ALLEGRO_KEY_MAX; ++i)
            {
                if (al_key_down(&kbdstate, i))
                    return true;
            }
            return false;
        }

But the al_get_keyboard_state() function seems to be very slow and slow down my loop. There was no problem with Allegro 4.4 and keypressed() function.

Is there a way to check if a key is waiting in the input buffer ?

Thanks

torhu

Member #2,727

September 2002

The "proper" way in Allegro 5 is to check for keyboard events in your event loop. If you just need to wait for an arbitrary keypress, you can do something like the code I posted in the thread to linked to.

If you are already in the event loop, waiting for any key is just this:

do
    al_wait_for_event(event_queue, &event);
while (event.type != ALLEGRO_EVENT_KEY_DOWN);

But you should probably check for at least ALLEGRO_EVENT_DISPLAY_CLOSE too, and set an "exit game" flag somewhere.

By the way, use <code></code> tags

---
Smokin' Guns - spaghetti western FPS action

zelda007

Member #12,303

October 2010

Hi,

No it is not possible to use an event pool in my case because I need to continue executing the code even if the key is not pressed...

In fact, the exact behaviour of keypressed() in Allegro 4.4

My "loop" game :

#SelectExpand
  1bool quit = false;
  2while (!quit) {
  3
  4   // some code
  5
  6   /*** Here we must not block the execution ****/
  7   if (keypressed())
  8   {
  9     // get the key pressed
 10     int key = getKeyFunction(...);
 11     if (key == ALLEGRO_KEY_DOWN) // do some stuff
 12     else if (key == ALLEGRO_KEY_Q) quit = true; // quit for example
 13     else if (......) // other stuff
 14   }
 15   /**********************************************/
 16
 17   // some code 
 18
 19} // end loop

Is there any way to do this ?

torhu

Member #2,727

September 2002

You can just empty the event loop each time, and ignore everything that you don't care about. You can use al_get_next_event, which doesn't block.

Not sure why you don't implement a proper event loop, though. Her is an example: https://wiki.allegro.cc/index.php?title=Allegro_5_Tutorial/Timers

---
Smokin' Guns - spaghetti western FPS action

zelda007

Member #12,303

October 2010

OK I will try.

Because I don't really program a game with allego. It is an IA and I use Allegro only for displaying statistics. That is why I don't really have a game loop with FPS ans so on.

Thanks

torhu

Member #2,727

September 2002

Is this more or less what you need?

#SelectExpand
  1ALLEGRO_EVENT_QUEUE *event_queue;
  2ALLEGRO_EVENT event;
  3bool quit = false;
  4
  5event_queue = al_create_event_queue();
  6al_register_event_source(event_queue, al_get_keyboard_event_source());
  7
  8while (!quit) {
  9    // some code
 10    
 11    /*** Here we must not block the execution ****/
 12    while (al_get_next_event(event_queue, &event))
 13    {
 14        if (event.type != ALLEGRO_EVENT_KEY_DOWN)
 15            continue;
 16        
 17        switch (event.keyboard.keycode)
 18        {
 19            case ALLEGRO_KEY_DOWN: // do some stuff
 20                break;
 21            case ALLEGRO_KEY_Q:
 22                quit = true; // quit for example
 23                break;
 24            default: // other stuff
 25                break;
 26        }
 27    }
 28    /**********************************************/
 29    // some code
 30
 31} // end loop
 32
 33al_destroy_event_queue(event_queue);

---
Smokin' Guns - spaghetti western FPS action

tobing

Member #5,213

November 2004

Or maybe you want to use

al_get_keyboard_state

to retrieve the current state of your keyboard, then use

al_key_down

to check if a specific key is pressed in that state.

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