Are there any recommended blogs or whitepapers that talk about making the AI in an RPG game feel more real? (Specifically in turn based combat.)
I know something must be out there, but I am only finding papers that talk about algorithms behind the AI. I am looking more along the lines of "this is what makes a computer opponent feel alive". Taking risks, going easy, retreating, etc....
So many awesome answers, and I wish I could accept several of them. Thanks everyone!
Mistakes. Nothing is worse than an AI opponent who can headshot you from fifteen miles away, or always picks the perfect winning strategy. It breaks the immersion and makes it apparent that you're playing a routine. Mistakes can make the AI seem more human.
Many FPS games force the AI to miss with its first few shots, warning the player that the AI is there, before going for the kill.
Strategy games could sometimes select a suboptimial strategy, or when evaluating threats may purposefully ignore some proportion of them.
A racing game I worked on calculated when the player was nearby, and then rolled a dice to make the AI cars in front of him understeer through the corner or blow a tyre. It was praised for its realistic AI.
However creating imperfect AI is still something of a challenge. You have to make convincing mistakes, at a convincing rate, rather than perform perfect action after perfect action until making a ridiculous blunder. That can be even worse than playing just a perfect AI. For instance, the programmer working on the racing AI above spent a lot of time on modelling how a car understeers, and what inputs the AI needs to make to cause a convincing understeer. As always, playtesting is vital.
Here's a good article on what goes into producing these kind of mistakes: http://www.gamasutra.com/view/feature/3947/intelligent_mistakes_how_to_.php
Others have talked about AI, logic, planning, and the importance of making mistakes. And all of these are good and useful in the development of AI.
But the question was about what makes a computer opponent feel alive, and that isn't achievable through AI. It just isn't. Players don't judge a character in a game based upon their strategic level choices; they judge it based on much smaller things.
To make a computer opponent feel alive, what you need is a comprehensive set of high-quality animations and sounds (vocals, especially) for the opponent. The player can't see the AI. He can't hear it, he can't experience it, he can't know what the opponent is thinking. The appearance of "this character is a living entity" is presented to the player entirely through the animations playing on the character, and the sounds being produced by the character (which again, will mostly be vocals).
It's important for the character to react to stimuli around him; to look at things nearby, to touch objects nearby (when appropriate to do so), to appear startled when surprised, and to show other emotions when appropriate.
When talking about these things, it's important to minimise repeats. If the character uses the same "attack" animation every time he attacks, he's never going to feel alive. If he plays a single looping "idle" animation when he's not doing anything else, he's not going to feel alive. If he says the same voice quip twice (especially consecutively), that breaks the illusion that the character is alive.
And that's pretty much it. If the opponent that you're trying to make seem alive is physically present in your game, then your success at making them seem alive will mostly be determined by the graphics and sound shown to the player.
If the opponent that you're trying to make seem "alive" isn't actually present in the game, as is the case in Chess and StarCraft, then feel free to disregard this reply; your best bet is to follow the AI-focused replies.
Here's a list of some simple concepts that can make your opponent more vivid:
Intent
Give the player some way of divining the 'intent' of the AI. This could be as simple as having them yell out "Quantity over Quality" before attempting an accurate headshot attack, "Flank him" while attempting to get behind you, or "Take the leader, nothing else matters" before attacking the protagonist. You could also get more complex, for example, have them give some sign language to their teammates, then change the behaviour of those teammates.
Desperation
As the opponent gets closer to death, you can give them a sense of desperation. Change their tactics at certain health milestones. Make their later stages more panicky, with greater risk taking on their part (going for the hail mary, rather than slow chipping). Visually communicate this as well (more exaggerated animations, pulsing veins, etc).
Go out with a Bang.
Give them a death that makes the fight with them something worth repeating. Grunts keel over animatedly. Bosses soliloquize. If it's a proud character, make them refuse to give you the kill, and deal the last of their damage to themselves. You get the drift.
I do recommend this google IO talk it is about google doodle pacman. At cca 18:00 they start to speak about personality of ghosts in pacman. It is really stuning how simply you can put personalities into the simple path finding.
Google I/O 2011: The Secrets of Google Pac-Man: A Game Show
Whole video is worth watching. I really recommend it.
I don't know about any such blogs, but since a tactical turn-based RPGs is my second favorite genre right after roguelikes, I'll write you a blog post. From my experience, it was not a difficulty of tactical AI in a RPG or RTS which often put me off, but its opposite: AI's complete short-sightedness and absence of team decisions. Human will never play like this.
Back then, when I still viewed JRPGs as a pinnacle of game design, I once tried to make a "typical japanese TRPG" with heavy focus on tactical turn-based combat like Final Fantasy Tactics. As always, it became just a tech demo for pathfinding and AI, so I'll share my thoughts on the subject.
Most of these TRPGs don't bother with AI much. Player's fun out there comes not from a complex tactical or strategical challenge, but from general farming and abusing AI in a funny way. So it doesn't matter much that their AIs do things no human would ever do. Usually it's sufficient to have a stupid AI and balance it out with game design in way that it never needs to see more than one move in advance and only use best short-term moves. Of course it never feels real, but who cares? This just feels wrong, I want to believe it is possible to create fun based on a battling complex AI actions instead of farming and steamrolling. Unnecessary maybe, and time-consuming as well, but possible.
Remembering original Final Fantasy Tactics and its hardcore mod FFT 1.3, I set the following goals for human-like and fun to play AI:
I thought that I will tackle #1 with emergent behaviours, #2 with different personalities and human-like "semi-random" strategy choice, #3 with keeping hard-coding to a minimum and a careful testing.
So what are these behaviours I'm what talking about, is it a scripted sequence of abilities to use? A top ability from a weighted list? Nope, what I had in mind was a combination of a desired intelligence, personality type and a role derived from currently available abilities and weapons. You can describe this combination as a "stupid berserking damage dealer" or "smart defensive healer". So AI specializations, like classes or professions, e.g. an Archer AI which uses bow to shoot arrows with some set of predefined generic archer ability combos like Take Aim or Arrow Shower, become logically emergent instead of hard-coded.
Basically, it is important to detect and operate on these roles: damage dealer, damage soaker, disabler, skirmisher, healer, buffer/debuffer, area of effect'er; usually, one character will perform at least two of these roles.
To make a tactical fun out of this we want for behaviours to handle several cases solidly:
Simplest case. A lot of weak goblins ambush our heroes. Perceived threat is obvious, goblins will try to overwhelm player with each goblin having a stupid berserk personality with some primitive melee abilities, perceived weakness is also obvious, like baiting goblins to a single armored and fire-resistant character, then casting a series of fire-based AoE spells in that general direction. Find a damage soaker, find an AoE'er, specialize the damage soaker for AoE'er damage type, send the damage soaker to the goblin mass, cast a damaging AoE spell when goblins group around.
Usual case to test out simple team interactions. Player encounters a knight, an archer, a mage and a cleric. Perceived threat is now more complex, various interactions become available. YOu can already see possible roles and its combinations. Cleric will buff and heal, mage will dish out complex but high-damaging magic things, knight will either charge someone or defend a mage, archer will help knight by sniping those who try to run away from him or making his defence strategy more comple, this will depend on knight's choice. Personalities for enemies may be decided randomly turning the same encounter into unique experience. Player will have to decide what is the best strategy with units he currently has, and if AI would try to do the same on the other side of the screen, it would be interesting.
Complex case to test out team interactions and strategic planning. There is a battle where you confront a gang of four assasins (clever careful damage dealer+skirmisher). Few in numbers, with menacing appearance, their perceived threat lies in skillful and deadly attack, and perceived weakness is that it's easy to reduce overall strength with just a single assasin killed. So naturally they're clever, they use abilities that work well with each other and can focus fire player's most dangerous characters; seriously injured ones retreat, heal and buff themselves to rejoin the battle. Obviously, player will try to nuke one of them first, and assasins will have to soft-counter this easy strategy, so it will be a less dominant.
Hard case for lots of strategy. There are several squads of enemies with each squad leader deciding best local tactical moves, and then a best global strategic decision is selected to benefit all squads.
Impossible case. Add a general to decide a strategy, and have squad leaders implement it to the best of the squads abilities.
It's a lot of letters already, so long story short, implementation was a mess and I never got past a "hard case", but even then this approach to a fun tactics felt doable. I started with FSMs but had to abandon that approach quickly, it became an entangled mess of states and transitions impossible to debug. After a while I settled with semi-autonomous ability perception based characters as in "sense-think-act" paradigm with behaviour trees for possible individual actions, a global strategy affecting possible team actions based on possible individual actions, also a bastardized version of something like N-Gram statistical prediction was tossed in.
How has this worked out? Surprisingly well, AI even read my mind several times, but I grew tired and abandoned it since there were more than enough convincing flaws:
I guess my approach was mediocre at best, if not outright bad, and AI was buggy and pain in the ass to develop further, but even then I had some really fun time playing against it, almost as if playing with a distracted kid, which is still better than Tactics Ogre :)
Don't always make it respond to your action X with action Y. As you evaluate each potential action add a random fudge factor so the AI doesn't always pick the same option but it chooses something reasonable.
Evaluate if an attack has a reasonable chance of succeeding or at least doing meaningful damage. Too many games simply have scripted attack routes that a human can learn and use to ambush the AI over and over.
One thing I see suggested a lot is to have the AI communicate its "thoughts" to the player in some way. This is often done in first-person shooters by having the enemies (unrealistically) shout out their plans to the player (i.e. "flank him!", "he's over there!", etc.).
At the end of the day, players know they're playing against an AI, so anything smart that the AI does without first informing the player can just be dismissed as cheating.
When talking about game NPCs most people associate liveness with intelligence, but emotion would probably be a much better indicator.
A hostage NPC in a bank robbery might just be sitting on the floor not doing anything "intelligent" but trembling, crying, holding a picture of family would bring an otherwise dull NPC to life.
The same thing is true for enemy NPCs. They would get enraged or fearful if you keep headshotting his pals. If you're sneaking around you could hear some rookies that are hesitant in going into combat. You could overhear their leader doing an inspiring speech to get the morale up.
Take a look at the Heider-Simmel Illusion where a psychologist shows that people have a tendency to see human-like behaviour everywhere, even in super abstract shapes. The video has no realistic animations, audio or models, but it has emotion.
Often, we think of "how do we create A.I.?"
That is skipping the big question, "What IS A.I. ?"
This talk from TED.com that I watched some years ago, shared a very inspiring approach to the definition of Artificial Intelligent.
If you want your players to feel that the enemies are "intelligent" then this will provide a high-level answer, and essentially a whole new way of thinking about A.I., which is the "ability to predict"
http://www.ted.com/talks/jeff_hawkins_on_how_brain_science_will_change_computing.html
To me, "feeling alive" means that the character act as you would think it would in real life.
People in real life have needs, motivations, fears, flaws. They talk, they react with each other if it is a group, they flee because they care for their own life.
If they are military or trained, they have tactics.
So maybe you should check in the field of human behavior, so in human sciences, not in computer sciences.
