Earlier I claimed that if Steamhammer has defilers out, it is probably winning. It’s true but misleading. Steamhammer’s game plan is such that it doesn’t try to win in the middle game (though it may win accidentally); the midgame is about holding the enemy off, getting upgrades, and growing the economy. When its drone count reaches 75, Steamhammer switches to all army production and its military strength grows rapidly—and that is the same time that defilers come into their own. When it reaches the late game, whether there are defilers or not, Steamhammer will be hitting hard and very likely winning, because if it weren’t winning it would probably have lost already. The late game is Steamhammer’s strongest phase.
Nevertheless, Steamhammer’s defiler usage has grown skillful enough that it definitely contributes to the bot’s strength. It’s an important milestone, because good defiler usage is critical to strong zerg play. Defilers are complicated, and zerg cannot reach its potential without mastering them. Steamhammer is far from mastering defilers, but I think it has become more adept with them than any other bot.
The original description of the defiler implementation is still accurate. Bugs have been fixed and refinements made, but the structure is unchanged.
that laser precision
I picked this game TyrProtoss-Randomhammer because it shows off Steamhammer’s precision and fluidity in defiler spellcasting. The precision was always there; the fluidity was reached by a long road with a year’s worth of bug fixes and other improvements. In the first picture, Steamhammer is about to start its decisive final attack. The attack would have won with or without defiler support. Accurate defiler spells made it effortless.
Steamhammer chooses plague because it looks like the fight will feature zealots versus hydras. The plague is actually a little weak. The defiler (selected and a little hard to see) is hemmed in by friendly units and cannot move forward, and Steamhammer hasn’t seen all the approaching enemies yet, so it plagues only 3 zealots. With a short delay for the opposing armies to close, it could have plagued more enemies, but it is not able to figure that out. Still, the plague helped in the battle.
Once the front zealots have died, Steamhammer has a fuller view of the situation, and realizes that the enemy has mostly dragoons left. The defiler (which has the energy upgrade) casts swarm, consume, consume, then a second swarm. The swarms are accurately placed to nullify the dragoons and drive the enemy back, bringing the fight into the natural. In the picture the defiler has just cast the second swarm, and it instantly consumes again.
The defiler is again stuck behind friendly units for a time, but protoss is forced back to the ramp. As zerg units spread out to raze the enemy natural, the defiler becomes free to move and drops a perfect plague on the ramp. Every protoss unit on the ramp is hit, and the zerg melee units that are in contact are untouched. No better plague is possible.
Steamhammer is awkward in maneuvering its defiler, and it is unable to foresee better opportunities that will arise in the near future. But when a spell goes down, it is often close to the best that is possible at that moment. It’s plenty good for now.
potential to turn the game
One defiler spell can make the difference between losing and winning. In practice, Steamhammer needs more skills before that will happen often in its games, but the examples here offer a foretaste. The game Steamhammer-McRave I picked to show the brute power of plague.
The first defiler of the game wandered carelessly into the front lines, stood on top of an isolated lurker, and got stormed to death. The defiler didn’t know the best place to go, that’s one weakness, and Steamhammer only makes 1 defiler at a time, that’s another weakness. An alert opponent can pick off the defiler and earn a respite. When the second defiler of the game joined the fray, this happened:
It’s a fun game, worth watching through. At the time of the picture, Steamhammer had been slowly twisting the situation into its favor from far behind, but McRave was still winning. The game could have gone either way. After this massive plague, turning a whole phalanx of zealots into straw, McRave’s army was broken and it quickly collapsed.
Here’s a picture from a different Steamhammer-McRave game. The red stuff all over the protoss natural is from 3 active plagues cast one after another by one defiler. The defiler just died; it sacrificed itself amidst the zealots (at the white spot of a dragoon hit) to get the third plague off, the one currently spreading over dragoons in the rear. The sacrifice was worth it. The protoss army was hollowed out, giving zerg time to consolidate an economic advantage and win. Without those plagues, McRave would have been able to move out and take the game with its bigger army (though I’m not sure it would have chosen to).
Here is a third example of a turnaround plague, from Steamhammer-MadMixT. After playing well much of the game, Steamhammer went astray and collapsed under a terran attack. It was about to lose its main and the game when a defiler risked its life to throw a plague over the core of the terran force, reducing the units to eggshells. Plague hurts terran more than protoss, which has shields. It then took only a few zerg units to clear the attack, partly due to terran’s disorganized movement, and with a return to superior play, Steamhammer slowly clawed its way to a win.
keeping active
Steamhammer is weak at using defilers in defense. I think it’s the widest remaining gap in defiler play. But it’s pretty good at using defilers in attack. I chose the game Steamhammer-MadMixP to show how, in the best case, Steamhammer can keep its defiler active through a long attacking sequence. The game itself is not very interesting, but watch the finishing attack which starts at around 17:30 from across the bridge to the terran natural.
It starts with a plague. If I didn’t miss anything, the sequence that follows is consume, consume, swarm, consume, consume, consume, plague, consume, consume, swarm, consume, consume, swarm, consume, consume, consume, swarm, consume, plague, consume, consume, consume, plague, consume, consume, consume, plague, consume, consume—and the last enemy building is destroyed. The defiler was stuck behind friendly units for short stretches, and otherwise busy every moment supporting the raging attack. Even though not all the activity was useful, the ability to keep constantly active is valuable.
blunders
Steamhammer does make mistakes in casting defiler spells, though rarely serious ones. Plague doesn’t account for moving units. It can miss fast-moving enemies altogether, for example trying to plague a group of corsairs and smearing only bare ground. In an active fight it can unintentionally plague its own units, which do not realize that they are moving into a danger zone. (It’s also perfectly willing to intentionally plague its own units, if that lets it splash more enemies. The calculation simply adds damage done to enemies and subtracts damage done to self.)
Dark swarm is thorny. Steamhammer only partially understands it. In Randomhammer-tscmoop2 the defiler cast a swarm that helped the enemy—with hydras on hand versus zealots and a reaver as well as the cannons and dragoons, swarm was a poor idea in the first place, and this swarm placement defends the enemy and does not open a path to attack. Oops. The research tab shows that plague was almost but not quite finished.
improvements needed
Why is Steamhammer weak with defensive dark swarm? To lay down swarm over lurkers and hold a position, or to force marines back with zerglings under swarm, you have to coordinate the swarm with the combat units. The defiler knows that swarm over lurkers is a great idea, and the combat simulator knows it too, in an approximate way. The lurkers themselves have no inkling; when their targets retreat, the lurkers will pick themselves up and obliviously step out of the swarm and die. Even something as simple as rendering hydralisks invulnerable to air attack is beyond Steamhammer. The hydras pay no attention.
Steamhammer’s squad code is already fragile from having too many skills tacked on, and needs to be rethought and rewritten. I’m reluctant to add complicated coordination skills before tackling that, so this weakness will likely be around for a while. It is a severe weakness, though, because defense is a critical use of defilers. Darn it, but there are times when only invulnerability can save you.
Besides the lack of coordination, there is no planning ahead. Defilers live in the moment and know nothing beyond. With prediction and planning, greater things could be accomplished with fewer resources.
More basically, the tendency of the defiler to get stuck behind friendly units reminds me that Steamhammer needs another fundamental skill: Smooth unit movement. Human players know that the defiler’s position is important, and move other units so that the defiler gets where it needs to be. And more generally, the missing skill shows in things like awkward movement through choke points, and clumsy collisions when squads cross paths.
I have a few simple ideas for how to control multiple defilers at once without blowing out cpu usage or seeing them simultaneously plague the same enemies. I expect I’ll implement that before SSCAIT this year. With 2 or 3 defilers in the Ground squad, defenders won’t have time to draw breath between spells.
Someday I’ll implement defiler drops. Zerglings with adrenal glands upgrade might as well be wrecking balls. Drop a defiler and some zerglings off to one side, swarm, swarm, and pick up the defiler for another go later while the lings rip down buildings. It’s cheap to do and expensive to defend against.
