"Bad guy" AI for games

[rdefabri]

I was playing Raymaze 2000 and I noticed some interesting AI for the "bad guys".  That had me thinking - how do you build in that AI in a game?

Of course, it depends on the type of game, some have far easier models.  I'm just curious how you build the logic, and what that might look like - not so much the code, but the logic and how it works.

[Rybags]

A lot of it from back in the day was pretty primitive.

These days game AI is a lot more complex but we're talking multi GB games on PC and console there.  Homebrewed legacy system games we still have those old limitations of lack of memory, slow CPUs and limited instruction sets.

 

There's plenty of articles describing AI these days like pathfinding etc.  There's some technical descriptions of arcade Pacman to be had - each ghost has it's own behaviours that can be taken advantage of and it's worth reading up on.

[rdefabri]

24 minutes ago, Rybags said:

A lot of it from back in the day was pretty primitive.

These days game AI is a lot more complex but we're talking multi GB games on PC and console there.  Homebrewed legacy system games we still have those old limitations of lack of memory, slow CPUs and limited instruction sets.

 

There's plenty of articles describing AI these days like pathfinding etc.  There's some technical descriptions of arcade Pacman to be had - each ghost has it's own behaviours that can be taken advantage of and it's worth reading up on.

I'll have to check out some articles - the concepts other than basics are new to me, but it's definitely something worth knowing.  As I think through creating some games of my own (should I ever get there), this always looms as an unknown for me, particularly for something where the "bad guys" chase or follow you.

[glurk]

A lot of the "old days" programmers just made it up as they went along.  Hobbyist programmers BITD didn't have research or articles to look at.  There's a lot to be said about just getting some stuff onscreen and moving, then just playing around with the code to see what works.  Fun and educational, IMO...  🤪

[rdefabri]

1 minute ago, glurk said:

A lot of the "old days" programmers just made it up as they went along.  Hobbyist programmers BITD didn't have research or articles to look at.  There's a lot to be said about just getting some stuff onscreen and moving, then just playing around with the code to see what works.  Fun and educational, IMO...  🤪

Funny enough, I was thinking decision trees, but then felt maybe not so efficient.  In doing some research here, I stumbled across a comment from another person about using decision trees - so I guess my brain is functioning somewhat properly!

[NRV]

15 hours ago, rdefabri said:

I was playing Raymaze 2000 and I noticed some interesting AI for the "bad guys".  That had me thinking - how do you build in that AI in a game?

You could try to look for some kind of source code, or disassemble the original Z80 roms (from the arcade version), or maybe look at the 6502 NES version (not the exact same game, but maybe the enemies have similar behaviors).

What I did was to look at a couple of youtube longplay videos and also played the original game in Mame, until I have an idea of the algorithms behind those behaviors.

Sure, is not that simple with the more complex behaviors, but I wanted them to be good enough, not perfect.

In fact I remember seen some videos where an enemy did something that I could not explain with my final models, but at that point it could even be a bug in the original code , so 99% was good enough for me.

In the end you cannot really do it perfect without looking at the original code.

 

After you have the basic behaviors in a nice list of steps and conditions you can start thinking about algorithms.
This is going to be easier if you have experience with those.
But for ""AI"" so simple as this, probably this list of steps is already your algorithm.
Then implementing this in your chosen language will depend on how much experience you have with it.
There is no shortcut for all this, you just start with simple things and move to the complex ones.. baby steps as they say (and time and patience).

 

As an example, one of the behaviors for the first enemy is that it tries to rotate toward the player's "perpendicular" direction, every time that it gets to an intersection in the maze.

 

Then if the enemy is moving up, and gets to an intersection or a front collision, the final code look more like this:

 

    .proc BehaviorUpFollowTarget

 

    // if there is a CounterClockwise exit and (playerX < enemyX) rotate CCW
    // if there is a Clockwise exit and (playerX >= enemyX) rotate CW
    // if there is no front collision continue front
    // else turn CW, CCW or back..

 

And there is equivalent code for when the enemy is moving right, left or down.

 

[+MrFish]

On 9/15/2022 at 3:01 AM, NRV said:

...or maybe look at the 6502 NES version (not the exact same game, but maybe the enemies have similar behaviors).

What NES game are you referring to?

 

[Traxx]

Nes Yuu Maze

 

[+MrFish]

44 minutes ago, Traxx said:

Nes Yuu Maze

Thanks.

 

No wonder I couldn't find it: I was looking in my carts folder. It's a Famicom disk; and one that I did already have. Never played (or heard of) it before, though.

 

[NRV]

Yes, that one.

 

https://strategywiki.org/wiki/Yuu_Maze

 

http://gaming.moe/?tag=yuu-maze

 

Sadly, it seems it was kind of bad.

[+MrFish]

33 minutes ago, NRV said:

Sadly, it seems it was kind of bad.

I played it a little bit. The gameplay seems alright, but it's no graphical masterpiece. The music isn't so great either, but passable.

 

[popmilo]

I like to think of ai as living agents where each one first has to know "where it is", then motivation, something where it needs to go, and in the and different ways how to move... Most of the time decision about next action is easy, unless it's complex game like RTS or similar. Many times it's enough to decide if it needs to move up/down/left/right and just do that once, repeat...

 

Pacman that was mentioned for example had those kinds of "period of random wandering..." replaced after some time "chase the player". It's just a flag at start of certain ghost routine. After you pass that decision it's all about doing h/v movement as needed.

You'll need counters, timers, path finding, sometimes even acceleration, speed, position, gravity etc... Then comes collision detection, bounding boxes etc... Fun times ahead