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Euphoria over Bad AI in Backbreaker?
by Dave Mark on 06/21/10 08:19:00 pm   Expert Blogs   Featured Blogs

The following blog post, unless otherwise noted, was written by a member of Gamasutra’s community.
The thoughts and opinions expressed are those of the writer and not Gamasutra or its parent company.

 

 [This post originally appeared on Intrinsic Algorithm's IA on AI blog, May 26, 2010] 

I was looking at a review of the new football game, Backbreaker, by the blogger, Pastpadre, and I found an interesting combination of observations. First, for those that don't know, Backbreaker is a football game that is developed by NaturalMotion. They are known first and foremost for their Euphoria physics engine that creates contextually realistic human body motion. Seeing as one of the biggest complaints about sports games—and football ones in particular—is that the human body physics begins to look canned and repetitive, you would think NaturalMotion had a bit of a head start in that area. The problem is, that isn't all people gripe about with football games.

While I commend NaturalMotion for attempting to move things forward in this area, there are plenty of things that need to be addressed, if not solved, if the genre is to advance further. Physics isn't necessarily on the top of the list. But hey, that's what they do.

This is particularly close to my heart because I'm an AI designer and a huge football fan. I am especially fond of football because of the deep intricacy of the team-based strategy that has to happen on every play. Of course, this is exactly the issue that is the hardest to address from an AI standpoint. Sports games—again, football ones in particular—are ridiculously hard to craft good AI for. For an industry that struggles to put together FPS squad tactics for 2 or 3 people, coordinating 11 people supposedly working together while being interfered with by 11 other people who are also working together is a tall order. The Madden franchise has been doing a passable job of this for some time. Sure, there are golden paths that bubble to the surface all the time, but those seem to be fewer and farther between.

Anyway, in this review, the author points out some interesting frustrations. He addresses it briefly in the first paragraph but I believe it summarizes things well (emphasis mine):

Reaction has been mixed with most gamers enjoying the Euphoria physics, polarization on the single camera angle, and the troubling CPU AI leading to the most concern.

(Brief aside: Who uses "CPU AI"? Not only is that redundant, it says the same thing twice.)

I will skip over his impressions of how Euphoria works. If you want to know all that happy-happy stuff, you can watch a Euphoria sales reel. I will address the AI-specific stuff. He goes on to comment about some of the specifics of how the AI falls flat on its face (emphasis mine).

The offensive output by the CPU has been pitiful. I’ve yet to give up more than a couple first downs on a single drive and still haven’t been scored on. The biggest reason is that the CPU turns the ball over a lot. In four minutes of gameplay it’s been close to an average of three picks thrown by the CPU. In the final demo video I posted I had three picks in three drives off the best offensive team in the game. That was with me being out of the play in all instances and the CPU just making bad passes.
This is summed up by the clincher which is my point here:
No matter how great the physics are I would not be able to play a football game if the CPU throws 10+ picks each time out.

This certainly seems to be an example of tunnel-vision on a pet feature while ignoring (or being incapable of addressing) the rest of the game that people actually want to experience. Is this a Euphoria sales demo or a football game? This is something that is more prevalent in the game industry that we care to admit. It isn't just Euphoria—or even physics—as the bad guy either. Swap in "game design", "story", "cool weapons", "sexy chick outfits", "huge environments" or whatever. AI is often the expression of your world. If your AI is broken, it severs the emotional connection to the game.

He continues:

The CPU goes with a jump pass way too often, whether it be springing forward or backwards, many times resulting in an interception. These aren’t instances where jumping to make a pass even would make some sense as the CPU would have been better off with their feet set.

Again, this apparently is broken decision logic. For those that don't know football, in the pros a "jump pass" is a rare event only used in certain situations. Commentators will typically hammer on a QB for not throwing with his feet set. In fact, theoretically, you could do a football game without even including an animation for a jump pass and no one would really notice all that much. Therefore, for the author to notice that this happening too often is rather telling.

More:

The CPU defensive back AI has been terrible in instances where they aren’t running in stride. When they continue to run in stride they seem to play the ball pretty well. If they stop (like on a comeback route or a pass lobbed up for grabs) they’ll start to go the wrong way, make a terrible attempt at the ball, or just stand there. Several times I’ve completed passes with multiple defenders in the area who played the ball horribly wrong. They’ve just stood there and watched the ball go over their heads or watched the receiver make an easy catch.

Again, I'm guessing this is either lazyness on the part of the development team, not knowing about football, or an inability to solve the problem. I hope it is the latter. The 2nd one is not acceptable if you are actually making a football game. The first... well...

A few more. Apparently it is not just the player AI that is troubling:

Penalties have been really iffy to say the least. I’ve seen roughing the passer called in multiple situations when it shouldn’t have been. I have seen a pass interference [im]properly called in two instances, called once when there was clearly no interference, and in several other situations seen receivers taken completely out before the ball arrives and no penalty called. There also seems to be an issue with roughing the kicker (primarily on punts) where your CPU controlled players commit the penalty way too often and out of the user’s control. I haven’t seen this one much but it has been widely reported.
So this has to do with the logic for detecting penalty situations. These should be, in effect, simple rule-based systems. For example,

if (contact(player, receiver) 
&& !TouchBall(receiver)
&& CatchableBall(receiver))
&& ((BallThrown() || ReceiverDownField())...

If you are botching up your static rule-based systems, then doing the contextual player-reaction AI is going to be a bitch.

Naturally, bad AI tends to lead to exploits:

Exploits have already been found with QB sneaks and the blocking of punts and field goals. These things could really damage the online play experience. The QB sneak problem, combined with the ability to no-huddle because of the lack of fatigue and not having to worry about injuries, could ruin online play. If blocked punts and kicks are prevalent online everyone will end up going for it on 4th downs.

This is the natural result... and is always a game-killer. If there is an obvious dominant strategy, you have now taken Sid Meier's "interesting choices" and condensed them down into "choose this to win". Many games with bad AI could still thrive in the online world. However, in a game where you only control 9% of your team and are entirely dependent on the other 91% for success, you can still do all the right things and still get rolled. That is not fun.

My point with all of this really has very little to do with the game itself and really less to do with the Euphoria engine. In fact, a quick browse through YouTube shows that there are some people who think the AI is just fine (although watching the videos and descriptions shows that people don't really know what AI is or what good AI might look like). That being said, your mileage may vary. My point was that of the juxtaposition of the two points the author was making: you need more than pretty physics to make a compelling game.

This is really only a modified version of the graphics vs. AI debates. Originally, studios made pretty games with bad AI (and even bad physics). Now we seem to have moved on to making better physics... and with products like Euphoria, even better physics that take the load off of AI programmers trying to figure out what human reactions should be. None of that solves stupid AI play, though. And until we do that, we are going to be seeing otherwise decent games get shelved.


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Comments


Laurie Cheers
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Natural Motion are based in Oxford. I don't think it would be very surprising if the team had no idea about American Football.

Shawn Lee
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Bravo. Thank you SO much for writing this. I couldn't agree more.


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