Last week in Part One of this article, Steven Woodcock took inventory of the current state game AI, based on the roundtables he led at the 2000 Game Developers Conference. Now in Part Two, Ensemble Studios' Dave Pottinger looks at what the future holds for game AI, and University of Michigan Professor John E. Laird discusses bridging the gap between AI researchers and game developers.

As I slowly reclined back into the seat of the last E3 bus this spring, I was certain of two things: some really great games were coming out in the next year and my feet hurt like hell. A lot of the games that created a buzz featured excellent AI.Since my fellow Ensembleites assured me (repeatedly) that no one really cared to hear about my feet, I thought I'd use this space to talk about some of the games coming out in the next 18 months and the new and improved AI technology that will be in them.

Better AI Development Processes and Tools

AI has traditionally been slapped together at the eleventh hour in a product's development cycle. Most programmers know that the really good computer-player (CP) AI has to come at the end because it's darn near impossible to develop CP AI until you know how the game is going to be played. As the use of AI in games has matured, we're starting to see more time and energy spent on developing AI systems that are modular and built in a way that allows them to be tweaked and changed easily as the gameplay changes. This allows the AI development to start sooner, resulting in better AI in the final product. A key component in improving the AI development process is building better tools to go along with the actual AI.

For Ensemble's third real-time strategy (RTS) game, creatively code-named RTS3, we've spent almost a full man-year so far developing a completely new expert system for the CP AI. It's been a lot of work taking the expert system (named, also creatively, XS) from the in-depth requirements discussions with designers to the point where it's ready to pay off. We've finally hit that payoff and have a very robust, extensible scripting language.

Interesting new entity AI features will be a key component in Cataclysm.

The language has been so solid and reusable that, in addition to using it to write the CP AI content, we're using it for console and UI command processing, cinematic control, and the extensive trigger system. We also expect to use XS to write complicated conditional and prerequisite checking for the technology tree; this way, the designers can add off-the-wall prerequisites for research nodes without programmer intervention. Finally, we will also use the XS foundation to write the script code that controls the random map generation for RTS3. The exciting aspect of XS from a tools standpoint is that we will have XS debugging integrated with RTS3's execution. For fans who used the Age of Empires II: The Age of Kings (AoK) expert-system debugging (a display table of 40 or so integer values), this is a huge step up, since XS will significantly increase the ease with which players can create AI personalities.

Better NPC Behavior

In the early days of first-person shooters, non-player characters (NPCs) had the intelligence of nicely rounded rocks. But they've been getting much better lately -- look no further than Half-Life's storytelling NPCs and Unreal Tournament's excellent bot AI. The market success of titles such as these has prompted developers to put more effort into AI, so it looks as if smarter NPCs will continue to show up in games.

Grey Matter Studios showed some really impressive technology at E3 with Return to Castle Wolfenstein. When a player throws grenades at Nazi guards, those guards are able to pick up the grenades and throw them back at the player, adding a simple but very effective new wrinkle to NPC interactivity. A neat gameplay mechanic that arises out of this feature is the player's incentive to hold on to grenades long enough so they explode before the guards have a chance to throw them back. Thankfully, Grey Matter thought of this and has already made the guards smart enough not to throw the grenades back if there's no time to do so.

Watch out for those tricky grenade-throwing guards when you get off of the gondola in Return to Castle Wolfenstein.

More developers are coupling their AI to their animation/simulation systems to generate characters which move with more realism and accuracy. Irrational did this with System Shock 2 and other developers have done the same for their projects. The developers at Raven are doing similar things with their NPC AI for Star Trek: Elite Force. They created a completely new NPC AI system that's integrated into their Icarus animation system. Elite Force's animations are smoothly integrated into the character behavior, which prevents pops and enables smooth transitions between animations. The result is a significant improvement to the look and feel of the game. I believe that as the use of inverse kinematics in animation increases, games will rely on advanced AI state machines to control and generate even more of the animations. As a side benefit, coupling AI to animation gives you the benefit of more code reuse and memory savings.

Better Communication Using AI

Since the days of Eliza and HAL, people have wanted to talk with their computers. While real-time voice recognition and language processing are still several years off, greater strides are being made to let players better communicate with their computer opponents and allies.

For example, in our upcoming Age of Empires: The Age of Kings expansion pack, The Conquerors, we've enabled a chat communication system that lets you command any computer player simply by sending a chat message or selecting messages from a menu. Combined with AoK's ability to let you script your own CP AI, this lets you craft a computer ally that plays on its own and lets you have conversational exchanges with it in random-map games. This is a small step toward the eventual goal of having players talk to their computer allies in the same way as to humans. Unfortunately, we still have to wait a while for technology to catch up to our desire.