Enemy AI Movement

no-reply@allegro.cc (ObscurePaulie) — Mon, 11 May 2015 17:31:37 +0000

Hi guys I was wondering if you could help me by explaining in simple terms as I'm new to Allegro coding, how I implement Finite State Machine AI into my game? Below is the coding I'm using but it's just not working. I know one problem is that the state isn't changing to IDLE during playing, so that is something that needs addressing. However, I also tried it without the states in and just used the chasing state code in my playing state and still nothing happens my enemies just fly across the screen regardless.

Any help on this would be greatly appreciated as it's the last part of my game that needs solving

#SelectExpand
   1//global variables
   2const int NUM_BULLETS = 5;
   3const int NUM_ENEMIES = 5;
   4const int NUM_EXPLOSIONS = 5;
   5enum STATE{ TITLE, PLAYING, GAMEOVER, IDLE, CHASING, CONTINUE};
   6float CheckDistance(Player &player, Enemy enemy[], int size);
   7float AngleToTarget(Enemy enemy[], int size, Player &player);
   8
   9Player player;
  10Enemy enemy[NUM_ENEMIES];
  11
  12//prototypes
  13void InitPlayer(Player &player, ALLEGRO_BITMAP *image);
  14void DrawPlayer(Player &player);
  15
  16void InitEnemy(Enemy enemy[], int size, ALLEGRO_BITMAP *image, ALLEGRO_SAMPLE *explode);
  17void DrawEnemy(Enemy enemy[], int size);
  18void StartEnemy(Enemy enemy[], int size);
  19void UpdateEnemy(Enemy enemy[], int size);
  20void CollideEnemy(Enemy enemy[], int size, Player &player, Explosion explosions[], int eSize);
  21
  22void ChangeState(int &state, int newState);
  23
  24int main()
  25{
bool done = false;
bool draw = true;
int FPS = 60;
int state = -1;
int threshold = 175;
enum KEYS { UP, LEFT, RIGHT, DOWN, SPACE };
bool keys[5] = { false, false, false, false, false };

if (!al_init())
{
  al_show_native_message_box(0, 0, "Error", "Falied to initialize allegro", 0, 0);
  return -1;
}
  39
display = al_create_display(ScreenWidth, ScreenHeight);
  41
if (!display)
{
  al_show_native_message_box(0, 0, "Error", "Falied to initialize the display", 0, 0);
  return -1;
}
  47
al_install_keyboard();
al_init_primitives_addon();
al_init_image_addon();
al_init_font_addon();
al_init_ttf_addon();
al_install_audio();
al_init_acodec_addon();
  55
playerImage = al_load_bitmap("Ship.png");
enemyImage = al_load_bitmap("alien4.png");
  58
ChangeState(state, TITLE);
  60
srand(time(NULL));
InitPlayer(player, playerImage);
InitBullet(bullets, NUM_BULLETS, bulletImage, laser);
InitEnemy(enemy, NUM_ENEMIES, enemyImage, explode);
InitExplosions(explosions, NUM_EXPLOSIONS, explosion);
  66
font18 = al_load_font("arial.ttf", 18, 0);
timer = al_create_timer(1.0 / FPS);
event_queue = al_create_event_queue();
  70
al_register_event_source(event_queue, al_get_timer_event_source(timer));
al_register_event_source(event_queue, al_get_keyboard_event_source());
al_register_event_source(event_queue, al_get_display_event_source(display));
  74
al_start_timer(timer);

while (!done)
{
  ALLEGRO_EVENT ev;
  al_wait_for_event(event_queue, &ev);
  81
  if (ev.type == ALLEGRO_EVENT_TIMER)
  {
    draw = true;
  85
    if (state == TITLE)
    {
  88
    }
    else if (state == PLAYING)
    {
      UpdateExplosions(explosions, NUM_EXPLOSIONS);
      UpdateBullet(bullets, NUM_BULLETS);
      StartEnemy(enemy, NUM_ENEMIES);
      UpdateEnemy(enemy, NUM_ENEMIES);
      CollideBullet(bullets, NUM_BULLETS, enemy, NUM_ENEMIES, player, explosions, NUM_EXPLOSIONS);
      CollideEnemy(enemy, NUM_ENEMIES, player, explosions, NUM_EXPLOSIONS);
  98
      if (state == IDLE)
      {
        if (threshold > CheckDistance(player, enemy, NUM_ENEMIES))
          ChangeState(state, CHASING);
      }
      else if (state == CHASING)
      {
        if (threshold < CheckDistance(player, enemy, NUM_ENEMIES))
          ChangeState(state, CONTINUE);
        else
        {
          float angle = AngleToTarget(enemy, NUM_ENEMIES, player);
          enemy[NUM_ENEMIES].y += (2 * sin(angle));
          enemy[NUM_ENEMIES].x += (2 * cos(angle));
        }
      }
      else if (state == CONTINUE)
      {
        UpdateEnemy(enemy, NUM_ENEMIES);
      }
      if (player.lives <= 0)
        ChangeState(state, GAMEOVER);
    }
    else if (state == GAMEOVER)
    {
 124
    }      
  }
 127
  else if (ev.type == ALLEGRO_EVENT_KEY_DOWN)
  {
    switch (ev.keyboard.keycode)
    {
    case ALLEGRO_KEY_DOWN:
      keys[DOWN] = true;
      break;
    case ALLEGRO_KEY_LEFT:
      keys[LEFT] = true;
      break;
    case ALLEGRO_KEY_RIGHT:
      keys[RIGHT] = true;
      break;
    case ALLEGRO_KEY_UP:
      keys[UP] = true;
      break;
    case ALLEGRO_KEY_ESCAPE:
      done = true;
      break;
    case ALLEGRO_KEY_SPACE:
      keys[SPACE] = true;
      if (state == TITLE)
        ChangeState(state, PLAYING);
      else if (state == PLAYING)
        FireBullet(bullets, NUM_BULLETS, player);
      else if (state == GAMEOVER)
        ChangeState(state, PLAYING);
      break;
    }
  }
  else if (ev.type == ALLEGRO_EVENT_KEY_UP)
  {
    switch (ev.keyboard.keycode)
    {
    case ALLEGRO_KEY_DOWN:
      keys[DOWN] = false;
      break;
    case ALLEGRO_KEY_LEFT:
      keys[LEFT] = false;
      break;
    case ALLEGRO_KEY_RIGHT:
      keys[RIGHT] = false;
      break;
    case ALLEGRO_KEY_UP:
      keys[UP] = false;
      break;
    case ALLEGRO_KEY_SPACE:
      keys[SPACE] = false;
      break;
    }
  }
  else if (ev.type == ALLEGRO_EVENT_DISPLAY_CLOSE)
  {
    done = true;
  }
 183
  if (draw && al_is_event_queue_empty(event_queue))
  {
    draw = false;
 187
    if (state == TITLE)
    {
      al_draw_bitmap(Title, 0, 0, 0);
    }
    else if (state == PLAYING)
    {
      al_draw_bitmap(background, 0, 0, 0);
      DrawPlayer(player);
      DrawBullet(bullets, NUM_BULLETS);
      DrawEnemy(enemy, NUM_ENEMIES);
      DrawExplosions(explosions, NUM_EXPLOSIONS);
 199
      al_draw_textf(font18, al_map_rgb(255, 0, 0), 5, 5, 0, "Lives: %i", player.lives);
      al_draw_textf(font18, al_map_rgb(255, 0, 0), 5, 580, 0, "Score: %i", player.score);
    }
    else if (state == GAMEOVER)
    {
      al_draw_bitmap(GameOver, 0, 0, 0);
 206
      al_draw_textf(font18, al_map_rgb(255, 0, 0), ScreenWidth / 2, ScreenHeight / 2, ALLEGRO_ALIGN_CENTRE, "Final Score: %i", player.score);
    }
    al_flip_display();
    al_clear_to_color(al_map_rgb(0, 0, 0));
  }
}
 213
al_destroy_display(display);
al_destroy_event_queue(event_queue);
al_destroy_timer(timer);
al_destroy_bitmap(playerImage);
al_destroy_bitmap(enemyImage);
 219
return 0;
 221
 222}
 223void InitPlayer(Player &player, ALLEGRO_BITMAP *image = NULL)
 224{
player.ID = PLAYER;
player.x = 55;
player.y = ScreenHeight / 2;
player.lives = 5;
player.speed = 6;
player.boundx = 25;
player.boundy = 25;
player.score = 0;
player.frameWidth = 50;
player.frameHeight = 50;
 235
if (image != NULL)
  player.image = image;
 238}
 239void DrawPlayer(Player &player)
 240{
al_draw_bitmap(player.image, player.x - player.frameWidth / 2, player.y - player.frameHeight / 2, 0);
 242}
 243void InitEnemy(Enemy enemy[], int size, ALLEGRO_BITMAP *image = NULL, ALLEGRO_SAMPLE *explode = NULL)
 244{
for (int i = 0; i < size; i++)
{
  enemy[i].ID = ENEMY;
  enemy[i].live = false;
  enemy[i].speed = 4;
  enemy[i].boundx = 15;
  enemy[i].boundy = 15;
 252
  if (image != NULL)
    enemy[i].image = image;
  if (explode != NULL)
    enemy[i].explode = explode;
}
 258}
 259void DrawEnemy(Enemy enemy[], int size)
 260{
for (int i = 0; i < size; i++)
{
  if (enemy[i].live)
    al_draw_bitmap(enemy[i].image, enemy[i].x - 10, enemy[i].y - 15, 0);
}
 266}
 267void StartEnemy(Enemy enemy[], int size)
 268{
for (int i = 0; i < size; i++)
{
  if (!enemy[i].live)
  {
    if (rand() % 500 == 0)
    {
      enemy[i].live = true;
      enemy[i].x = ScreenWidth;
      enemy[i].y = 50 + rand() % (ScreenHeight - 100);
 278
      break;
    }
  }
}
 283}
 284void UpdateEnemy(Enemy enemy[], int size)
 285{
for (int i = 0; i < size; i++)
{
  if (enemy[i].live)
  {
    enemy[i].x -= enemy[i].speed;
  }
}
 293}
 294void CollideEnemy(Enemy enemy[], int size, Player &player, Explosion explosions[], int eSize)
 295{
for (int i = 0; i < size; i++)
{
  if (enemy[i].live)
  {
    if (enemy[i].x - enemy[i].boundx < player.x + player.boundx &&
      enemy[i].x + enemy[i].boundx > player.x - player.boundx &&
      enemy[i].y - enemy[i].boundy < player.y + player.boundy &&
      enemy[i].y + enemy[i].boundy > player.y - player.boundy)
    {
      player.lives--;
      enemy[i].live = false;
      StartExplosions(explosions, eSize, player.x, player.y);
      al_play_sample(enemy[i].explode, 0.5, 0, 1, ALLEGRO_PLAYMODE_ONCE, NULL);
    }
    else if (enemy[i].x < 0)
    {
      enemy[i].live = false;
    }        
  }
}
 316}
 317float CheckDistance(Player &player, Enemy enemy[], int size)
 318{
for (int i = 0; i < size; i++)
{
  if (enemy[i].live)
    return sqrt(pow((float)player.x - enemy[i].x, 2) + pow((float)player.y - enemy[i].y, 2));
}

 325}
 326float AngleToTarget(Enemy enemy[], int size, Player &player)
 327{
for (int i = 0; i < size; i++)
{
  if (enemy[i].live)
  {
    float deltaX = (enemy[i].x - player.x);
    float deltaY = (enemy[i].y - player.y);
    return atan2(deltaX, deltaY);
  }
}
 337}
 338
 339void ChangeState(int &state, int newState)
 340{
if (state == PLAYING)
{
  al_stop_sample_instance(SongInstance);
}
 345
state = newState;
 347
if (state == PLAYING)
{
  InitPlayer(player);
  InitBullet(bullets, NUM_BULLETS);
  InitEnemy(enemy, NUM_ENEMIES);
  InitExplosions(explosions, NUM_EXPLOSIONS);
 354
  al_play_sample_instance(SongInstance);
}
 357
 358}

no-reply@allegro.cc (l j) — Mon, 11 May 2015 19:44:35 +0000

      else if (state == PLAYING)
      {
        UpdateExplosions(explosions, NUM_EXPLOSIONS);
        UpdateBullet(bullets, NUM_BULLETS);
        StartEnemy(enemy, NUM_ENEMIES);
        UpdateEnemy(enemy, NUM_ENEMIES);
        CollideBullet(bullets, NUM_BULLETS, enemy, NUM_ENEMIES, player, explosions, NUM_EXPLOSIONS);
        CollideEnemy(enemy, NUM_ENEMIES, player, explosions, NUM_EXPLOSIONS);

        if (state == IDLE)
        {
          if (threshold > CheckDistance(player, enemy, NUM_ENEMIES))
            ChangeState(state, CHASING);
        }

It will never be able to enter the IDLE state.
Separate the game state and enemy state.

enum GameState { Title, Playing, GameOver };
enum EnemyState { Idle, Chasing, Continue };
...
GameState gameState;
...
enemy[i].state;

Aside from all that:

            float angle = AngleToTarget(enemy, NUM_ENEMIES, player);
            enemy[NUM_ENEMIES].y += (2 * sin(angle));
            enemy[NUM_ENEMIES].x += (2 * cos(angle));

This doesn't make much sense.
You seem to be trying to calculate the angle to a target but you pass a complete array and then you write outside of the bounds of the enemy array.

You probably want something like this.

for (int i = 0; i < NUM_ENEMIES; ++i)
{
    if (enemy[i].state == IDLE)
    ...
}

If you want to make an object follow another object in the most simple way, this would be faster than atan and cos/sin

float dx = target.x - object.x;
float dy = target.y - object.y;
float length = sqrt(dx * dx + dy * dy);
float x = dx / length * desiredLength;
float y = dy / length * desiredLength;
object.x += x;
object.y += y;

no-reply@allegro.cc (ObscurePaulie) — Mon, 11 May 2015 21:24:03 +0000

I have made some of the changes suggested here, now the only thing I am unsure on is what is the desiredLength meant to be?

I don't have that as a variable anywhere in my code.

So what am I supposed to set it to?

I have this set up and all it is doing now is restarting my game every time an enemy should be following the player.

#SelectExpand
      for (int i = 0; i < NUM_ENEMIES; i++)
      {
        if (enemy[i].state == IDLE)
        {
          if (threshold > CheckDistance(player, enemy, NUM_ENEMIES))
            ChangeState(state, CHASING);
        }
        else if (enemy[i].state == CHASING)
        {
          if (threshold < CheckDistance(player, enemy, NUM_ENEMIES))
            ChangeState(state, CONTINUE);
          else
          {
            float desiredLength = 50;
            float dx = player.x - enemy[i].x;
            float dy = player.y - enemy[i].y;
            float length = sqrt(dx * dx + dy *dy);
            float x = dx / length * desiredLength;
            float y = dy / length * desiredLength;
 20
            enemy[i].x += x;
            enemy[i].y += y;
          }
        }
        else if (enemy[i].state == CONTINUE)
        {
          UpdateEnemy(enemy, NUM_ENEMIES);
        }
      }

no-reply@allegro.cc (beoran) — Tue, 12 May 2015 00:21:33 +0000

You are changing the game's state, not the enemy's state, and the check isn't correct.

if (enemy[i].state == IDLE)
{
  if (threshold > (player, enemy[i]))
  ChangeState(state, CHASING);
}

In stead check a bit more thoroughly and set the state of the enemmies correctly.

if (enemy[i].state == IDLE)
{
  if ((enemy[i].alive) && (threshold > CheckOneDistance(player, enemy[i]))) { 
    enemy[i].state = CHASING;
  }
}

...
float CheckOneDistance(Player &player, Enemy &enemy)
{
   return sqrt(pow((float)player.x - enemy.x, 2) 
             + pow((float)player.y - enemy.y, 2));
}

Also do this for the other item states. Keep at it, you're learning as you go!

no-reply@allegro.cc (l j) — Tue, 12 May 2015 03:31:08 +0000

desiredLength is the magnitude of the vector, or simply put how fast you want your object to move.

no-reply@allegro.cc (ObscurePaulie) — Tue, 12 May 2015 03:50:20 +0000

Beoran, you sir are an absolute genius! I can not thank you enough!

I have it sort of working now with the help from yourself and Taron.

Only problem I have now is that my enemies seem to fly across the screen if they don't catch my player

and when I say fly I'm not meaning in a standard speed kinda way as they should be I mean literally too fast to attempt to shoot them

no-reply@allegro.cc (beoran) — Tue, 12 May 2015 08:43:26 +0000

Probably the speed of the ennemies is set too high somehow. Try to reduce the speed.

no-reply@allegro.cc (l j) — Tue, 12 May 2015 18:19:13 +0000

With the FPS being 60 and the desiredLength being 50, they'd move at 3000 units/second and the units being pixels in this case that would be 3000 pixels per second.

no-reply@allegro.cc (ObscurePaulie) — Wed, 13 May 2015 03:41:47 +0000

I know in my earlier code I had 50, that was just test numbers cos I was unsure of what to enter there. However, in my actual coding now I have the desiredLength set to 3 and my movements speed is only set to 4.

I commented out the code to make the enemies chase my player and they don't get super speedy, so it is something to do with this code here that is making my enemies go super speedy after so long...

#SelectExpand
      for (int i = 0; i < NUM_ENEMIES; i++)
      {
        if (enemy[i].state == IDLE)
        {
          if ((enemy[i].live) && (threshold > CheckDistance(player, enemy[i])))
            enemy[i].state = CHASING;
        }
        else if (enemy[i].state == CHASING)
        {
          if ((enemy[i].live) && (threshold < CheckDistance(player, enemy[i])))
            enemy[i].state = CONTINUE;
          else
          {
            float desiredLength = 1;
            float dx = player.x - enemy[i].x;
            float dy = player.y - enemy[i].y;
            float length = sqrt(dx * dx + dy *dy);
            float x = dx / length * desiredLength;
            float y = dy / length * desiredLength;
 20
            enemy[i].x += x;
            enemy[i].y += y;
 23
            if ((enemy[i].live) && (threshold < CheckDistance(player, enemy[i])))
              enemy[i].state = CONTINUE;
          }
        }
        else if (enemy[i].state == CONTINUE)
        {
          UpdateEnemy(enemy, NUM_ENEMIES);
        }

no-reply@allegro.cc (beoran) — Wed, 13 May 2015 11:04:57 +0000

else if (enemy[i].state == CONTINUE)  {  UpdateEnemy(enemy, NUM_ENEMIES); }

This looks incorrect. Remember, you're looping over all enemies one by one, but UpdateEnemy updates many enemies at once. It doesn't make sense to do that in that particular place in your program. In stead, you should update the particular enemy[i] in the way you want it to be updated.

no-reply@allegro.cc (ObscurePaulie) — Wed, 13 May 2015 16:09:09 +0000

Yeah I noticed that myself last night and forgot to update my post. I just decided to take it out of my coding and just use the 2 states for my enemies, as I have the enemies moving across screen in that updateenemies function in my game state of playing anyway. Thanks for the help though