Archons do splash damage that affects all enemy units, included undetected units. That means that you can use an archon to, for example, kill a burrowed lurker that you can’t detect, by attacking one of your own units. The usual way is to park a sacrificial zealot on top of the lurker and attack the zealot with the archon; the archon will do full damage to the zealot and splash damage to the lurker.
Archon splash affects both ground and air. An archon attacking a zealot will damage a cloaked wraith that is in splash range. An archon attacking a floating ebay should clear spider mines in a small area (I haven’t tested to make sure).
Here’s how Skynet does it. Behaviour::createDefaultActions() recognizes the unit types and records possible micro actions to test and execute later:
if(unitType == BWAPI::UnitTypes::Protoss_Zealot || unitType == BWAPI::UnitTypes::Protoss_Archon)
{
firstTargets.insert(BWAPI::UnitTypes::Terran_Siege_Tank_Siege_Mode);
mMicroActions.push_back(MicroAction(new ArconZealotKillUnDetected(mUnit)));
}
When the micro action comes up for testing, it runs ArconZealotKillUnDetected::update(), which either fails the test and returns false or succeeds, executes the micro, and returns true.
Given the original archon or zealot in mUnit, it looks for the closest enemy unit that meets the conditions:
Unit lurker;
int lurkerDistance = std::numeric_limits<int>::max();
for each(Unit unit in UnitTracker::Instance().selectAllEnemy())
{
if(unit->exists() && !unit->isDetected() && (unit->isCloaked() || unit->getType().hasPermanentCloak() || (unit->getType() == BWAPI::UnitTypes::Zerg_Lurker && unit->isBurrowed())))
{
int thisDistance = mUnit->getDistance(unit);
if(thisDistance < lurkerDistance)
{
lurkerDistance = thisDistance;
lurker = unit;
}
}
}
if(!lurker || lurkerDistance > minDistance)
return false;
The variable is called “lurker” but it looks for any unit that is undetected and is temporarily cloaked (like a wraith or a unit under an arbiter), permanently cloaked (like a dark templar), or is a burrowed lurker. I skipped over the next bit of code: It checks for the other unit (of type typeToFind) and if it’s close enough puts it in other; if it has a zealot it looks for an archon, or if an archon it looks for a zealot. If it finds the needed other unit, it executes the micro:
if(typeToFind == BWAPI::UnitTypes::Protoss_Archon)
{
if(mUnit != UnitTracker::Instance().selectAllUnits(BWAPI::UnitTypes::Protoss_Zealot).getClosestUnit(lurker))
return false;
mUnit->move(lurker->getPosition());
return true;
}
else
{
if(otherDistance <= 14)
{
mUnit->attack(other);
return true;
}
else
{
mUnit->move(other->getPosition());
return true;
}
}
If the unit is a zealot (because typeToFind is archon) and it’s not the closest zealot, it bails so that the target doesn’t get swarmed by zealots—one volunteer at a time, please! The zealot moves to the position of the target. If the unit is the archon, it moves toward the zealot (not toward the target; this corrects for miscoordination that could occur if there’s more than one target around) or, if the zealot is within splash range of the target, attacks the zealot.
The bottom line is that Skynet has the basic skill, but its implementation is not sophisticated. It knows all the possible targets, but can only use a zealot as the sacrifice—pros in a pinch will use anything that works as the sacrifice. It doesn’t know that it could use a reaver instead of an archon. It doesn’t consider whether the sacrifice is worth the damage to the target (you’ll hurt your zealot and the cloaked wraith will probably escape). It does no preparation (keep the archon and zealot near each other if they may need to work together) and minimal coordination (if there’s an observer just out of range and approaching, you shouldn’t have bothered; if you have high templar around maybe you should storm it). If the target evades, Skynet may keep microing both units, leaving them out of the fight. But of course most bots don’t have even the basic skill.
Reminder: Other units that do splash can also kill undetected enemies this way. Reavers, sieged tanks, and lurkers are the prime splash-dealing candidates. Corsairs, firebats, valkyries, and infested terrans also have occasional uses. (Mutalisk bounces are technically not splash and do not hit undetected enemies.) And, of course, spell effects like nuke, irradiate, psionic storm, ensnare, and plague affect units whether they are detected or not. Ensnare and plague are particularly useful because they make cloaked units visible.
Near the end of this 2008 game, Stork fires on his own carriers with corsairs to hold off cloaked wraiths.
Tomorrow: Mine dragging.
