Scripting

So I was recently linked to an article about using scripting languages instead of 'real' languages. tl;dr, he talks about how scripting languages are just as powerful, just as fast, and frequently use a simpler syntax. They also compile separately, and can literally be treated as content, almost like a texture, or a map.

But, he somehow managed to briefly brush past the biggest reason why scripting languages are important to game development. They allow you to code for your game using a far higher level of abstraction! This is especially true for custom scripting languages, created for a specific game, a whole genre of games, or merely for games in general. One of my favorite examples of this is Age of Empires II, a game I spent significant amounts of time building and testing AI scripts for.


Though technically, I preferred it without the expansion. Martyrdom made monks really boring.

The fun thing is just how simple AI scripting is for AOE II. It lets you completely define the personality of the AI player, the style they play in, their priorities, the types of troops that they build, and on and on. Here's a quick snippet of what the language looks like:

(defrule
(strategic-number sn-minimum-town-size == military_townSize_1)
(soldier-count < military_townSize_army_1)
=>
(chat-local-to-self "Lowering town size to level 0.")
(set-strategic-number sn-minimum-town-size military_townSize_0)
(set-strategic-number sn-maximum-town-size military_townSize_0)
)

;Attack Now
;start timer
(defrule
(true)
=>
(chat-local-to-self "Activating attack delay timer.")
(enable-timer military_timer_attack_delay 1)
(disable-self)
)

;acknowledge timer w/ other conditions
(defrule
(strategic-number sn-minimum-town-size == military_townSize_6)
(not(enemy-buildings-in-town))
(timer-triggered military_timer_attack_delay)
=>
(chat-local-to-self "Attacking without town size attack.")
(chat-to-allies "31 Attack an Enemy Now")
(attack-now)
(disable-timer military_timer_attack_delay)
(enable-timer military_timer_attack_delay military_attack_delay_min)
)

As you can see, the syntax is extremely simple, almost LISP-like, but it's set up in a fashion where it's incredibly easy to define rules for the AI to follow. AOE II still uses an AI framework built into the game itself, but it does that to simplify the scripts that people would work with on a more frequent basis. It does mean there are a few things that are impossible for the scripter to change the behavior of, but that's alright in moderation.

Compare the above snippet with this bit from an XNA game that I'm currently working on.

case AIState.Check:
{
 AIFish fish = FindFish();
 if (fish != null)
 {
  target = fish;
  if (fish.size > size)
  {
   state = AIState.Run;
   stateTime = (float)gameTime.TotalGameTime.TotalSeconds + 3 + RandomUtil.CreateFloat(0, 2);

   Vector2 runDir = -(target.position - position);
   runDir.Normalize();

   dest = position + runDir * 400 * size + RandomUtil.CreatePoint(new Rectangle((int)(-200 * size), (int)(-200 * size), (int)(400 * size), (int)(400 * size))); 
  }
  else
  {
   if (RandomUtil.CreateFloat(0, 1) > 0.5f)
   {
    state = AIState.Hunt;
    stateTime = (float)gameTime.TotalGameTime.TotalSeconds + 3 + RandomUtil.CreateFloat(0, 2);
   }
   else
   {
    state = AIState.Wander;
    stateTime = (float)gameTime.TotalGameTime.TotalSeconds + 4 + RandomUtil.CreateFloat(0, 2);
    dest = position + RandomUtil.CreatePoint(new Rectangle((int)(-200 * size), (int)(-200 * size), (int)(400 * size), (int)(400 * size)));
   }
  }
 }
 else
 {
  state = AIState.Wander;
  stateTime = (float)gameTime.TotalGameTime.TotalSeconds + 4 + RandomUtil.CreateFloat(0, 2);
  dest = position + RandomUtil.CreatePoint(new Rectangle((int)(-1000 * size), (int)(-1000 * size), (int)(2000 * size), (int)(2000 * size)));
 }
} break;

Yeah, definitely not my prettiest bit of code, but that seems to be a theme with basic Finite State Machines when I code them. Imagine if I set up a basic framework, and did this in a custom scripting language? Quite possibly, I could reduce this into 3-4 lines of script, and easily swap out for different fish, types of fish, or even fish with different personality. When you have a really simple scripting language with which to express your ideas, then it suddenly becomes far easier to express more complex thoughts!

I think I'm going to leave it at that, there's plenty of other thing that the author of the article left out or glazed over, but I think this was one of the more important bits. Thanks for reading~