Expose the possible start locations for a player or force

[dgant]

I've attached a copy of the map Aztec 2.1. The map has three playable start locations but BWAPI exposes eight start locations. The inability to determine which of these start locations are playable is a(n extremely minor) missing feature.

This map was probably converted from an "Observers" style map. That means it was originally meant to be played in Use Map Settings with some people playing and some people just observing. So it has a Players force with three normal start locations, and an Observers force with four start locations in the middle of the map, with the intent that Observers would play Terran and lift off and watch the game via Share Vision.

At some point in the map's history, the Observers force was rendered unplayable, so on the surface it appears to be a normal ladder map. But from the perspective of bots, it's an 8 player map and the API doesn't expose any information which indicates otherwise.

(3)Aztec2.1.zip

[heinermann]

with the intent that Observers would play Terran and lift off and watch the game via Share Vision

If it were this situation then I'm fine with the behaviour. From the perspective of BWAPI they are participants in the game for 2 reasons:

1. An opponent player can do this legitimately.
2. UMS maps and even other game types can have all sorts of configurations, some of which could be mistakenly identified as this scenario.

BWAPI should be able to function on all maps and all game types so using base detection with minerals is not a legitimate way to determine participation either.

---

That being said I loaded the map up in Remastered and my own custom map editor to see what was going on, before realizing I didn't finish programming the player settings dialog in it. So I opened it in a hex editor to view the corresponding sections since it wouldn't open in SCMDraft. In OWNR the players are set to Inactive so these should indeed be excluded.

Relevant code here:

bwapi/bwapi/BWAPI/Source/BWAPI/GameEvents.cpp

Lines 169 to 187 in 3438abd

	for (int i = 0; i < BW::PLAYABLE_PLAYER_COUNT; ++i)
	{
	// Skip Start Locations that don't exist
	if (BW::BWDATA::Game.startPositions[i] == Positions::Origin)
	continue;
	// If the game is UMS and player is observer and race is not (UserSelect OR invalid player type), skip
	if ( this->getGameType() == GameTypes::Use_Map_Settings &&
	this->players[i]->isObserver() &&
	(bRaceInfo[i] != Races::Enum::Select ||
	(bOwnerInfo[i] != PlayerTypes::Computer &&
	bOwnerInfo[i] != PlayerTypes::Player &&
	bOwnerInfo[i] != PlayerTypes::EitherPreferComputer &&
	bOwnerInfo[i] != PlayerTypes::EitherPreferHuman)) )
	continue;
	// add start location
	startLocations.push_back(TilePosition(BW::BWDATA::Game.startPositions[i] - Position(64, 48)));
	}

There we do a naiive check to see if the start location is at the origin, when this is in fact incorrect. We need to

1. Determine which player types are valid (including invalid/extended/overflow types).
   • Specifically for UMS and whether their units will appear if they are preplaced or creatable with triggers.
2. Determine if players can have a start location at exactly 0,0 (I suspect yes for UMS).
3. Change the logic accordingly.