This post will be about the Brood War bot XIMP by Tomas Vajda. XIMP is an older bot, which hasn’t been updated since 2015. It got second place in the CIG and AIIDE in 2014. It also got second place in the SSCAIT of 2014/2015. Even now, three years after its last update it remains quite strong. So what makes XIMP so powerful?
First let’s take a look at at its strategy. XIMP is know for its iconic use of Carriers. The first thing it will do is build cannons at his natural. Lots of cannons.
With these defenses in place it will tech up straight to Carriers. It barely gets any other units before the carriers. Then it sends out groups of some four Carriers to destroy the opponent. Depending on what units the enemy has it may add Observers for detection, or Corsairs for more anti-air power.
On paper, there are some big problems with this strategy. In the first image I count 13 Photon Cannons. Those costs a total of 1950 minerals. Any human player who scouts that many cannons will know that he will be safe from attacks for a very long time. The obvious response would be to expand like crazy and overwhelm him. The better bots indeed know how to do this, or they use some other strategy which they know works.
There are however a lot of less advanced bots which don’t react well. There are the rush bots, which I mentioned in my previous post. These tend to suicide their units into the cannons and then they get wiped out by the carriers. There are some bots which are smart enough to see those cannons and decide to retreat. The retreat code often has problems though. They may not remember the cannons after they are out of their vision, and after retreating their units dive right back in. Some bots wait for a specific number of units before they decide to attack. However as soon as one or two units die they fall below the threshold and retreat again. In the mean time they take a lot of shots.
In fact, one of the first games of Brood War AI I watched was the semi finals of the SSCAIT of 2014/2015. This was a best of three series between XIMP and UAlbertaBot by Dave Churchill. UAlbertaBot repeatedly danced his Zealots in and out of range of the Cannons. XIMP won the series 2-0.
What can we learn from the successes of XIMP? Going for the theoretically better strategy isn’t always the most successful. It is often much better to stick to a simpler strategy and make sure you execute it well.