Editing MeleeStrategy/UnderstandingHawkOnFire

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== Melee Strategy - Understanding [[HawkOnFire]] ==

''By [[Kawigi]] - hopefully also looked over/edited by [[Rozu]]''

[[Rozu]] released the source to his breakthrough melee bot, [[HawkOnFire]], when he saw that people were genuinely interested in it some time ago, but hasn't packaged it with the bot.  Since then, I think it's been on everyone's todo list to take a look at it.  You can go see by going to http://www.robocoderepository.com/BotDetail.jsp?id=1575 and clicking on "Download Source".  If I refer to the source, I'll be referring to that source.  It appears that [[Rozu]] took some time to edit and fix up the code before uploading it here, and for the benefit of clarity, it compiles to be a bit larger than the barely-micro size that HawkOnFire normally is.  That having been said, with some analysis and tweaking, I got HawkOnFireOS under 700 bytes with no loss of functionality or performance that I can tell (so if you have something to use 50 bytes for, [[Rozu]], let me know).

=== Classes ===
[[HawkOnFire]] is made up of 2 classes:
* The main robot class
* the microEnemy class, which contains the location, energy, and whether or not the enemy is alive.  These are stored in a Hashtable in the robot class.

=== Functions ===
There are a few typical utility functions, calcPoint (which projects a point some distance away from a base location at some angle) and calcAngle (which finds the absolute bearing from one point to another).

[[HawkOnFire]] also overrides the onRobotDeath method to mark enemies as dead.

The primary magic in [[HawkOnFire]] lives in the <tt>evaluate</tt> and <tt>doMovementAndGun</tt> methods.  <tt>run</tt> doesn't do much besides set up and call these methods, and <tt>onScannedRobot</tt> just updates the enemies and handles target selection.

=== Globals ===
Most of these are pretty self-explanitory, but the Points declared should be explained:
* <tt>nextDestination</tt> is the point that [[HawkOnFire]] is trying to get to.
* <tt>lastPosition</tt> is the point that [[HawkOnFire]] is coming from last.
* <tt>myPos</tt> is where [[HawkOnFire]] is now.

=== Radar ===
Spins the radar in melee, InfiniteRadarLock in 1-on-1.

=== Gun ===
Not too exciting, the enemy's position is set in <tt>onScannedRobot</tt>, lines 54-57 turn the gun and fire.  Contrary to rumors, [[HawkOnFire]] does not always fire power-3 bullets - it's a little more aggressive than alot of small melee bots as far as firepower is concerned, but not as aggressive as bots with a dependable gun.  One feature that's worth pointing out is that target.energy/3 is in there, which is more than enough to kill the target at that point.  [[HawkOnFire]] doesn't want a low-energy target to get lucky after being hit :-)  Also, [[HawkOnFire]] always tries to target the closest living enemy, and likes to have its gun turned, and never fires when its energy is under 1.

=== Movement ===
[[HawkOnFire]] is a textbook example of [[MinimumRiskMovement]].  The point-generating function generates 200 points at random between 100 and 300 pixels away but no more than 80% of the distance to its current target (to avoid hitting other robots as much).

==== Risk Function ====
The <tt>evaluate</tt> method is [[HawkOnFire]]'s risk function, except for one part - the <tt>addLast</tt> variable that is passed in as a parameter is precomputed for consistency so that the same value is used when comparing for every point.  <tt>addLast</tt> is set to <tt>1 - Math.rint(Math.pow(Math.random(), getOthers()))</tt>, which makes it 1 most of the time with more bots on the field and 0 about half of the time in 1-on-1.  This variable determines whether <tt>lastPosition</tt> is used in the risk calculation.

Which leads us into <tt>evaluate</tt> itself.  Basically, after starting out the risk as addLast times an antigravity function on <tt>lastPosition</tt>, [[Rozu]] iterates through the enemies, and for each live one, adds the proposed risk to the total risk (called <tt>eval</tt>).  The formula is very simple and elegant (and I don't think I'm exaggerating to say that it's a breakthough in and of itself) - simply <tt>energy ratio * (1 + perpendicularity) / distanceSq</tt>.
* The energy ratio is the enemy's energy / [[HawkOnFire]]'s energy (but no more than 2) - this makes enemies with higher energy more "dangerous"
* perpendicularity is the absolute value of the cosine of the difference between the angle from the point to [[HawkOnFire]]'s current location and the angle from the point to the enemy.  This is 0 when the point is at a right angle and 1 if the point is directly toward or away from the enemy.
* distanceSq is the distance from the point to the enemy.

Once you understand this formula, you pretty much understand [[HawkOnFire]].

----

Great. Haven't read it yet, but I just must comment one of the first statement - "I think it's been on everyone's todo list to take a look at it." Ha! I have never even considered taking a look at it until this page came up. Now though I just might. Just need to fail in a few attempts at melee movements myself first. -- [[PEZ]]

I rather read pages like this than to look at the code. When looking at the code, I just see the code. When reading a description like above, I form my own ideas and try to implement them the way I see fit. Ofcourse once in a while I also copy things (like teamcommunication, circular targeting) but I still try to adapt and improve them to my needs. This is yet another excellent page. I wish that I could a) write such clear and informative page and  b) write such sophisticated and competetive bot.  -- [[GrubbmGait]]

Code or prose. Not too much difference for me (as long as the code is somewhat readable). It's just that I don't want to get to "coloured" by other peoples ideas before I try myself. I want to get those "ahhhh!" feels when I later try look at how people have approached the problems I have stumbled across. -- [[PEZ]]

I do not know if this has been said yet, but welcome back [[kawigi]]. Good to see you around the game still. -- [[jim]]

Nice page! I don't think that I have something to edit here. But anyway, I'm open to answer any questions as required. --  [[rozu]]

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