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Post-Play'em - Observations on Game AI

Posts Tagged ‘Opposing Fronts’

Odd Glitch in Company of Heroes

Thursday, February 11th, 2010

Just to be clear, I really like Company of Heroes. I have always been an RTS fan since the original Warcraft and progressing through Starcraft, Age of Empires/Kings and especially Empire Earth. That being said, CoH is very well done.

I only recently got around to grabbing the full version of the original CoH and the expansion, Opposing Fronts. (Thank you Valve weekend sales!) My prior posts here were only about the downloadable demo. Obviously, there are some significant differences in the full release version. I like them all.
Rather than continuing through the script-fest that campaign maps usually are, I have been playing a lot of skirmishes against the computer. I find a lot of the tactics by the computer to be pretty familiar for RTS games.
For example, as I mentioned in a prior post, it is obvious that there is a lot of influence mapping going on. If I find myself a little behind on producing units, I will often be drawn into a series of dashing from defense point to defense point as the computer picks on whatever is currently the weak spot. My only question in this situation is how much is the AI cheating with knowledge about my force disposition. I know that it is not that easy to discern what the computer has placed and entrenched… it seems like he knows where my weak spots are even if they are deep within my territory.
Anyway, as I was playing a skirmish map, I ran across something very odd. Normally, I had been playing against the “normal” level of difficulty. I had been winning fairly regularly against that level, however, and decided to ratchet it up one level. I was playing the Lyon map against the computer on “hard.”
Because this was a control point map, I was quite used to meeting the “normal” AI at the river as we battled for those 3 points. I figured that the “hard” AI would be just as quick to get to the river. However, I captured the first point… then the second… without seeing the AI at all. I began to suspect that either something was dreadfully wrong or that “hard” used a different tactic than “normal” – such as “build up and crush him” rather than “dash for the control points”. Not too long after that, it became obvious that something was indeed seriously amiss.
Thanks to the wonders of replay files, I was able to go back and witness what the computer did… or did not do. A video is included below.
I sent the video privately to my friend and colleague, Chris Jurney, who did much of the excellent AI work on CoH. He thought it was amusing as well. His speculation was that the Lua script exploded somehow. It obviously didn’t cease working entirely because we see some orders trickling through at times. He invited me to send him the replay file so that he could forward it on to the Relic programmer who is responsible for it now.
It doesn’t seem to be a problem with the map itself as I did go on to play a new match on that map on “hard” and it proceeded to hand me my buttocks as I expected. On the other hand, it may be a problem with a combination of that map, that difficulty level, and a randomly selected tactical approach that knocked a variable out of bounds or something. Regardless of the cause, this is a great example of how important testing is… and yet things still slip through.
Anyway, I will try to do more video captures of some games later – especially the view that shows how the computer is moving throughout the map during the game. That has been very interesting to analyze because it shows how the influence mapping and even the pathfinding is working as part of the decision making.
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