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