Development:AIScripts
Vega Strike has completely programmable python AI scripts--but often times just editing an XML file with a list of actions at various distances and probabilities is sufficient and quite a bit more performant
AI scripts are selected as follows: the following two excel files in the ai/ folder are consulted ai/VegaEvents.csv The VegaEvents file is a table mapping combat_roles of the attacker to roles of his target. Combat roles are stored in the Combat_Role column in units.csv For instance if my starship is a BOMBER and I am targeting a BASE then vega strike will look in row BOMBER and column BASE and find the beginning of the name of the AI script thus it would be bomber.* where * might be .agg.xml or .civ.xml depending on the next file:
ai/VegaPersonalities.csv VegaPersonalities is a list of a factions and what AI scripts they wish to use Each listed faction is followed by a comma and then by a space separated list of extensions to use on their AI script. so if bomber was selected from VegaEvents.csv and the faction is merchant which has the second column "scared scared civ" there will be a 1/3 chance that bomber.civ.xml will be selected, otherwise bomber.scared.xml will be selected
if the file is not found bomber.agg.xml will be searched then default.civ.xml then default.agg.xml (I believe .py files are also searched)
Once an XML file is selected, it is parsed every frame to select an AI behavior for the starship to use when attacking its target
The XML file selected has a simple format <AggressiveAI time="7"> is the header it tells the AI script how often to search for scripts and must be paired with a </AggressiveAI> at the very end of the file Between this header and footer is a list of actions that the AI is allowed to perform, each tagged by conditions that enable them to be selected and a priority to help the computer choose an action to perform
Lets take a look at an example:
<hull max=".03" script="drop cargo" time="1" priority="8"> <hull max=".03" script="afterburn turn away" time="10" priority="8"> </hull> </hull>
This says if the hull is at most .03 and the hull is at most .03 drop cargo for a second and then turn away for 10 seconds with a priority of 8 nested script actions are conjoined together and if all their conditions evaluate to true they are performed in sequence. Noticed in the above example we specified the hull being at most .03 *twice* so that the condition would be evaluated in the same manner both times---this simply enables us to tell the computer to perform those two actions in sequence so that the AI computer does not drop all cargo at once but only drops cargo every 10 seconds and runs away
Lets fish up a little more complex example:
<hull max=".6" script="evade up down" time="4" timetointerrupt="3" priority="7">
<fshield max=".25" script="evade up down" time="1" timetointerrupt="0" priority="7">
<rand max=".13" script="evade up down" time=".5" timetointerrupt="0" priority="7"/>
</fshield>
</hull>
This translates into: if the hull is at most at 60% strength, the forward shields are at most 25% and the random number generator selects a number with 13% probability then evade up and down for 4 seconds, 3 of which are uninterruptible, then evade up and down for another 1.5 seconds which are interruptible
This timetointerrupt parameter can ensure that an AI is not constantly shifting between decisions but instead actually follows through on an action. It can help the AI "commit" to finishing a task instead of being interrupted--and hence should be used with caution with scripts that could cause collision--because a collision-imminent decision (as we shall see in a bit) needs to interrupt other choices with a high priority
Collision Avoidance:
<meterdistance max="30" script="afterburn turn away" time="7" timetointerrupt="3" priority="6">
<rand min=".4" script="afterburn fly straight" time=".5" timetointerrupt="1" priority="6"/>
</meterdistance>
This part of the script says: if the distance is at most 30 meters (this is adjusted for speed and acceleration) then turn around for 7 seconds (3 of those are uninterruptible) and then fly away for another half second. This would hopefully direct an AI to avoid a collision instead of playing chicken with a human (or computer ) opponent
However all of the scripts we have talked about before have a higher priority, so they're not considered interruptible with this particular command.. .however the above commands also move the ship AWAY from the target---so they aren't really the type of thing that could result in an intentional collision
Attacking Script: The script that needs to be interrupted by the above script follows later in the file:
<meterdistance min="60" max="500" script="turn towards itts" priority="4" time="5">
<meterdistance max="500" script="turn towards" priority="4" time="8">
<rand min=".5" script="loop around" priority="4" time="5">
</rand>
</meterdistance>
</meterdistance>
This says "if the distance is between 60 and 500, is at most 500 and the random number generator gives a number that has probability 50% then turn towards the target, giving it itts lead if available, then turn towards it without lead, then loop around it. Notice that this script is entirely interruptible if the AI ever gets within 30--and since the priority is lower than 6, it will indeed be overridden by the afterburn turn away listed above. But the above script is essentially the bread and butter of the AI--it directs it to turn towards its opponent and shoot like crazy (the shooting is handled in C code right now)
Another important facet of this attacking part of the AI is to have something that's true in all conditions...this means including a fallback that happens if the random number fails like so:
<meterdistance min="60" max="500" script="afterburn veer away" priority="4" tim\
e="2">
<meterdistance max="500" script="turn towards" priority="4" time="8"> </meterdistance> </meterdistance>
and also some things to do if far away:
<meterdistance min="500" script="barrel roll" time="2" timetointerrupt="1"> <fshield max=".1" script="barrel roll" time="1"> </fshield> </meterdistance> <meterdistance min="500" script="barrel roll" time="2" timetointerrupt="1"> <bshield max=".1" script="barrel roll" time="1"> </bshield> </meterdistance> <meterdistance min="500" script="afterburn turn towards itts" priority="4" time="3"> </meterdistance>
Now as you may have noticed there are a lot of descriptions in script
script can be a python script (which executes turns, or fire commands, etc) or an XML script located in the scripts folder, but for the most part those scripts should simply be precanned ones that I've written in the Vega Strike C code
the prebaked scripts are listed as follows:
loop around fast
hits the afterburner and aims just to the left or above or right of the target in order to hopefully pass it and come around on its tail
aggressive loop around fast
hits the afterburners and vectors the thrusters to left or above the target while facing it and shooting at it and eventually coming around behind it
loop around slow
uses normal thrusters and aims just above or to the left or right of the target in an effort to pass it and get behind it
aggressive loop around slow
uses normal thruster to vector thrust just above or to the left or right of the target in an effort to pass it and get behind the target while shooting at it
loop around
uses whatever mode is selected in the vegastrike.config for use_afterburners and aims to above or to the left or right of the target in an effort to get past it and get on its tail
aggressive loop around
uses whatever mode is selected in the vegastrike.config for use_afterburners and vectors thrust to above or to the left or right of the target in an effort to get past it and get on its tail while aiming at it with its guns
barrel roll
hits the pitch and roll keys at the same time to get a corkscrew effect
veer away
vectors thrusters away from the target while facing it and shooting
veer away itts
vectors thrusters away from target while facing it with lead and shooting
veer and turn away
vectors thrusters away from target as well as turning away from target
veer and vector away
vectors thrusters away from target as well as turning away from target
afterburn veer away
vectors thrusters away from the target while facing it and shooting with afterburners engaged
afterburn vector away
vectors thrusters away from the target while turning away from target and hitting afterburners
match velocity
vectors thrusters such that the target velocity is matched
fly straight
fly in a straight line
fly straight afterburner
light afterburners and fly in a straight line
afterburn fly straight
light afterburners and fly in a straight line
do nothing
do not adjust velocity vector or turn--if target is in sights then shoot otherwise do nothing
take off
unknown
coast to stop
slow down to a stop
self destruct
unknown
take off every zig
unknown
afterburn turn towards
turn towards the center of the target with full afterburners
afterburn turn towards itts
turn towards where the target will be given the gun speed (lead) and shoot
cloak
cloak and evade
evade
turn left and right to evade fire
kick stop
stop as fast as possible
move to
fly to where the target is and stop
shelton slide
keep velocity the same while turning towards target
skilled afterburner slide
vector thrusters slightly away from the target, fire afterburners forward then aim towards the target and shoot
afterburner slide
aim slightly away from the target, fire afterburners forward then aim towards the target and shoot
stop
counteract momentum with thrusters and come to a stop
turn away
turn away from target using normal thrusters
afterburn turn away
turn away from target using afterburners if available
turn towards
turn towards target and fire at it without using afterburn
turn towards itts
turn towards target given lead and current guns and fire at it without using afterburn
drop cargo
drop all cargo
drop half cargo
drop half cargo
drop one cargo
drop a single cargo item
roll right
do a right roll at half power
roll right hard
do a right roll full power
roll left
roll left at half power
roll left hard
roll left at full power
evade left right
evade left and right (just like evade)
evade up down
evade up and down to avoid fire
afterburn evade left right
fire up afterburners and wiggle to the left and right
afterburn evade up down
fire up afterburners and wiggle up and down
For a description of what each of these do see hard_coded_scripts.cpp
