Starcraft AI blog

“Somebody” voted in a bunch of Steamhammer versus PurpleWave games. PurpleWave played different openings. Past versions of PurpleWave dominated Steamhammer with the forge-expand opening, taking advantage of Steamhammer’s mistaken macro decisions and weak scouting and tendency to collapse tactically in a big fight. But this PurpleWave has been losing some; it has new weaknesses. So the games are not the best, but they are still interesting.

Some of the games were proxy 2 gates. There were wins and losses, but I found those games not as interesting.

on La Mancha

This is the Steamhammer-PurpleWave game that Nepeta cast last Sunday, so I won’t go into detail. PurpleWave suffered bugs that caused it to warp buildings near the zerg forces and pull probes for no reason, so it did not develop its usual big advantage. What I find interesting about the game is the turning point, when zerg pulled decisively ahead: It was when protoss attacked the zerg natural and dealt great damage, destroying the drones.

The returning zerg army finally cleared the attack. The protoss army was trapped and could not retreat toward home. It should have “retreated” into the zerg main to try to deal more damage (and to pull the zerg army away from the front), but instead turned fatalistic and gave up without a fight. Meanwhile, zerg had many drones at other bases and quickly restored the losses, while the lost protoss army was not as easy to replace. The value of destroying drones depends not on the number of drones you kill, but on the number that survive somewhere....

on Icarus

This game was also a forge-expand, but the play was quite different. No obvious bugs bit. PurpleWave built 4 cannons, which is plenty for most circumstances... and Steamhammer busted them anyway.

Steamhammer killed probes too. Then I tore my hair out in frustration, because instead of pressing for the win, Steamhammer decided it was more important to simultaneously plant a spire, hatchery, evo chamber, and hydra den, and also grow its economy. Notice in the picture that, although Steamhammer has spent 4 drones on buildings, it is still ahead in workers—and PurpleWave has cautiously pulled probes for defense. The spire, by the way, was left unused until late. With 2 bases, PurpleWave eventually caught up from far behind and the game was on again.

Fortunes turned again, like last time, when PurpleWave overpressed and lost too much army at Steamhammer’s natural. Seconds after this picture, protoss went from ahead in army size to well behind. Zerg quickly replaced drone losses and soon broke into the protoss natural in return.

on Destination

PurpleWave went 2 gate zealots into expansion. Neither bot had much understanding of the situation. Steamhammer massed lings, an all-in play to smash the opponent. In practice it’s successful against most bots, but zerg ends up way behind in economy. Protoss can play defensively for a while and then win easily—that’s how Tyr protoss beats Steamhammer.

The game is not long or exciting. PurpleWave expanded in the face of the zerg swarm and did not have enough zealots. I include it to show how little bots understand strategy. In the picture, Steamhammer has half the workers of protoss. With any insight into the army-economy balance, you have to conclude that it is not a time for protoss to take a risk like expanding or moving out. The zealots again went fatalistic; as soon as they realized that they had lost, they stopped fighting and (unable to retreat far) were caught and died. You can also see that in the picture. Steamhammer has related weaknesses that are different but as severe.

PurpleWave might have had a chance if it retreated to the ramp and canceled the nexus. It was the best option, at least.

I expect that PurpleWave will fix its bugs before long and start winning again.

Next: More games, versus McRave and KillAll.