Spring RTS Engine

trying to think of a way to implement this idea from http://aichallenge.org/

under battle resolution in game specification: Is this possible?

I was thinking of taking a circle radius around my unit and finding all units in that circle, take # friends and # foes and adjusting UnitDamaged() by some percent multiplied by the # of friends(less damage) or foes(more damage)...any opinions? Will calculating all of this slow the game too much?

yes, that is possible and should not be too hard.
getting units in circle: Spring.GetUnitsInCylinder
http://springrts.com/wiki/Lua_SyncedRead#GetUnits

Will calculating all of this slow the game too much?

should be doable without too much slowdown, of course depends on number of units etc.

Maybe it will be faster to call Spring.GetUnitsInCylinder every n frames, (instead of every time a unit gets damaged) and store the results. Depends on how many units you have, how fast they shot etc.

sounds good, will try this out :)