public ProjectileManager(World world) {
      bullets=new Bullet[MAX_BULLETS];
      decals=new Decal[MAX_DECALS];
      for (int i=0; i<MAX_BULLETS; i++) {
         bullets[i]=new Bullet();
         bullets[i].addToWorld(world);
      }

      for (int i=0; i<MAX_DECALS; i++) {
         decals[i]=new Decal();
         decals[i].addToWorld(world);
      }
   }