Adicionar imagens que percorram a tela

[Mario Viero]

olá, gostaria de uma ajuda para saber como adicionar imagens que "fiquem descendo a tela" constantemente de tempo em tempo com o objetivo de criar obstáculos com elas.

#include <stdio.h>
#include <allegro5/allegro.h>
#include <allegro5/allegro_image.h>
#include <allegro5/allegro_acodec.h>
#include <allegro5/allegro_audio.h>


const float FPS = 60;
const int SCREEN_W = 640;
const int SCREEN_H = 480;
const int AVIAO_SIZE = 80;
enum MYKEYS {
   KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT, KEY_SPACE
};

int main(int argc, char **argv)
{
   ALLEGRO_DISPLAY *display = NULL;
   ALLEGRO_EVENT_QUEUE *event_queue = NULL;
   ALLEGRO_TIMER *timer = NULL;
   ALLEGRO_BITMAP *aviao_principal = NULL;
   ALLEGRO_SAMPLE *sample=NULL;//Audio
   float bouncer_x = SCREEN_W/2 - AVIAO_SIZE / 2.0;
   float bouncer_y = SCREEN_H-90 - AVIAO_SIZE / 2.0;
   bool key[4] = { false, false, false, false };
   bool redraw = true;
   bool doexit = false;

   if(!al_init()) {
      fprintf(stderr, "failed to initialize allegro!\n");
      return -1;
   }

   if(!al_install_keyboard()) {
      fprintf(stderr, "failed to initialize the keyboard!\n");
      return -1;
   }

   timer = al_create_timer(1.0 / FPS);
   if(!timer) {
      fprintf(stderr, "failed to create timer!\n");
      return -1;
   }
   if(!al_install_audio()){
      fprintf(stderr, "failed to initialize audio!\n");
      return -1;
   }

   if(!al_init_acodec_addon()){
      fprintf(stderr, "failed to initialize audio codecs!\n");
      return -1;
   }

   if (!al_reserve_samples(1)){
      fprintf(stderr, "failed to reserve samples!\n");
      return -1;
   }

   sample = al_load_sample("audio/somambiente.wav");
    if (!sample)
    {
        fprintf(stderr, "Falha ao carregar sample.\n");
        al_destroy_display(display);
        return false;
    }

   display = al_create_display(SCREEN_W, SCREEN_H);
   if(!display) {
      fprintf(stderr, "failed to create display!\n");
      al_destroy_timer(timer);
      return -1;
   }

    al_init_image_addon();
   aviao_principal =  al_load_bitmap("imagens/aviaoprincipal.png");
   if(!aviao_principal) {
      fprintf(stderr, "failed to create avio_principal bitmap!\n");
      al_destroy_display(display);
      al_destroy_timer(timer);
      return -1;
   }

   al_set_target_bitmap(aviao_principal);

  // al_clear_to_color(al_map_rgb(255, 0, 255));

   al_set_target_bitmap(al_get_backbuffer(display));

   event_queue = al_create_event_queue();
   if(!event_queue) {
      fprintf(stderr, "failed to create event_queue!\n");
      al_destroy_bitmap(aviao_principal);
      al_destroy_display(display);
      al_destroy_timer(timer);
      return -1;
   }

    al_register_event_source(event_queue, al_get_display_event_source(display));

   al_register_event_source(event_queue, al_get_timer_event_source(timer));

   al_register_event_source(event_queue, al_get_keyboard_event_source());

   al_clear_to_color(al_map_rgb(0,0,0));

   al_flip_display();

   al_start_timer(timer);

   while(!doexit)
   {
      ALLEGRO_EVENT ev;
      al_wait_for_event(event_queue, &ev);
      al_play_sample(sample, 1.0, 0.0,1.0,ALLEGRO_PLAYMODE_LOOP,NULL);

      if(ev.type == ALLEGRO_EVENT_TIMER) {
         if(key[KEY_UP] && bouncer_y >= SCREEN_H/2) {
                aviao_principal=al_load_bitmap("imagens/aviaoup.png");
            bouncer_y -= 4.0;
         }

         if(key[KEY_DOWN] && bouncer_y <= SCREEN_H - AVIAO_SIZE - 50) {
                aviao_principal=al_load_bitmap("imagens/aviaoprincipal.png");
            bouncer_y += 4.0;
         }

         if(key[KEY_LEFT] && bouncer_x >= 7.0) {
                aviao_principal=al_load_bitmap("imagens/aviaoleft.png");
                bouncer_x -= 4.0;
         }

         if(key[KEY_RIGHT] && bouncer_x <= SCREEN_W - AVIAO_SIZE - 7) {
                aviao_principal=al_load_bitmap("imagens/aviaoright.png");
                bouncer_x += 4.0;
         }

         redraw = true;
      }
      else if(ev.type == ALLEGRO_EVENT_DISPLAY_CLOSE) {
         break;
      }
      else if(ev.type == ALLEGRO_EVENT_KEY_DOWN) {
         switch(ev.keyboard.keycode) {
            case ALLEGRO_KEY_UP:
               key[KEY_UP] = true;
               break;

            case ALLEGRO_KEY_DOWN:
               key[KEY_DOWN] = true;
               break;

            case ALLEGRO_KEY_LEFT:
               key[KEY_LEFT] = true;
               break;

            case ALLEGRO_KEY_RIGHT:
               key[KEY_RIGHT] = true;
               break;
         }
      }
      else if(ev.type == ALLEGRO_EVENT_KEY_UP) {
         switch(ev.keyboard.keycode) {
            case ALLEGRO_KEY_UP:
                aviao_principal=al_load_bitmap("imagens/aviaoprincipal.png");
               key[KEY_UP] = false;
               break;

            case ALLEGRO_KEY_DOWN:
                aviao_principal=al_load_bitmap("imagens/aviaoprincipal.png");
               key[KEY_DOWN] = false;
               break;

            case ALLEGRO_KEY_LEFT:
                aviao_principal=al_load_bitmap("imagens/aviaoprincipal.png");
               key[KEY_LEFT] = false;
               break;

            case ALLEGRO_KEY_RIGHT:
                aviao_principal=al_load_bitmap("imagens/aviaoprincipal.png");
               key[KEY_RIGHT] = false;
               break;

            case ALLEGRO_KEY_ESCAPE:
               doexit = true;
               break;
         }
      }

      if(redraw && al_is_event_queue_empty(event_queue)) {
         redraw = false;

         al_clear_to_color(al_map_rgb(135,206,250));

         al_draw_bitmap(aviao_principal, bouncer_x, bouncer_y, 0);

         al_flip_display();
      }
   }


   al_destroy_bitmap(aviao_principal);
   al_destroy_timer(timer);
   al_destroy_display(display);
   al_destroy_event_queue(event_queue);
   al_destroy_sample(sample);

   return 0;
}