Editing revision 6 of FastTargeting/LinearTargeting

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''WaveSurfingChallenge Bot B:''
<pre>
		//This code goes in your onScannedRobot() event handler
		
		double bulletPower = Math.min(3.0,getEnergy());
		double myX = getX();
		double myY = getY();
		double absoluteBearing = getHeadingRadians() + e.getBearingRadians();
		double enemyX = getX() + e.getDistance() * Math.sin(absoluteBearing);
		double enemyY = getY() + e.getDistance() * Math.cos(absoluteBearing);
		double enemyHeading = e.getHeadingRadians();
		double enemyVelocity = e.getVelocity();
		
		
		double deltaTime = 0;
		double battleFieldHeight = getBattleFieldHeight(), battleFieldWidth = getBattleFieldWidth();
		double predictedX = enemyX, predictedY = enemyY;
		while((++deltaTime) * (20.0 - 3.0 * bulletPower) < Point2D.Double.distance(myX, myY, predictedX, predictedY)){		
			predictedX += Math.sin(enemyHeading) * enemyVelocity;	
			predictedY += Math.cos(enemyHeading) * enemyVelocity;
			if(	predictedX < 18.0 
				|| predictedY < 18.0
				|| predictedX > battleFieldWidth - 18.0
				|| predictedY > battleFieldHeight - 18.0){
				predictedX = Math.min(Math.max(18.0, predictedX), battleFieldWidth - 18.0);	
				predictedY = Math.min(Math.max(18.0, predictedY), battleFieldHeight - 18.0);
				break;
			}
		}
		double theta = Utils.normalAbsoluteAngle(Math.atan2(predictedX - getX(), predictedY - getY()));
		
		setTurnRadarRightRadians(Utils.normalRelativeAngle(absoluteBearing - getRadarHeadingRadians()));
		setTurnGunRightRadians(Utils.normalRelativeAngle(theta - getGunHeadingRadians()));
		fire(bulletPower);
</pre>

----
The following is an implementation that I currently use:
<pre>
	class LT extends Gun {
		double gunAngle(Tracker me, Tracker enemy, double bulletPower){
			double enemybearing = me.absoluteAngleTo(enemy);
			return Math.asin(enemy.velocity/Utils.bulletVelocity(bulletPower)*Math.sin(enemy.heading-enemybearing))+enemybearing;
		}
	}
</pre>
--[[Nfwu]]
----
=== Buggy Implementations ===
If anyone has time, these 2 algorithms are buggy. It would be great if someone could fix them, since they are both faster than the code I provided on the LinearTargeting page. --[[David Alves]]

''Geoff Buggy Implementation:''

<pre>
 do{	// Time it will take for a bullet to get to the current prediction	
   double bulletTravelTime = getDistance(getX(), getY(), predictX, predictY) / bulletSpeed;
   // Check where the enemy will be in that amount of time	
   predictX = Enemy.getX() + (Enemy.getVelX() * bulletTravelTime);	
   predictY = Enemy.getY() + (Enemy.getVelY() * bulletTravelTime);	
   // Check for likely contact with a wall and adjust the prediction	
   // accordingly	
   if (predictX < 18) predictX = 18;	
   if (predictY < 18) predictY = 18;	
   if (predictX &gt; getBattleFieldWidth() - 18) predictX = getBattleFieldWidth() - 18;	
   if (predictY &gt; getBattleFieldHeight() - 18) predictY = getBattleFieldHeight() - 18;
   // The miss factor is the difference between the time it takes	
   // for a bullet to get to the current prediction and the time it	
   // takes for a bullet to get to the new prediction	
   missFactor =	Math.abs(bulletTravelTime - getDistance(getX(), getY(), predictX, 
                predictY) / bulletSpeed));	
   bulletTravelTime = getDistance(getX(), getY(), predictX, predictY) / 14;
 } while (missFactor &gt; 0.01);
</pre>

It works fairly well, but I'm sure that I can improve the way that missFactor is calculated. The thing that I don't understand is why it doesn't work 90% of the time against Walls. I've been staring at it/tweaking it for too long to think properly now ;-p.

''Kawigi Buggy Implementation:''

I've taken a little time to also figure out some more geometric ways of doing it- this system always hits walls if he doesn't turn (and sometimes also gets him coming out of a turn, but I wouldn't depend on it).  I don't really add it into my bots, though, because it doesn't hit anyone except walls and the guys who stand still.
<pre>
double bulletv = 20-3*power;		//find bullet speed
/*
 * all the logic isn't here, I'd need to draw a picture to give you any idea what's going on.
 * The idea is I've constructed a triangle where you are at one corner, your opponent is on the second corner, 
 * and your opponent will be hit by your bullet at the third corner.  I use the Law of Sines:
 *	A/sine(a) == B/sine(b) == C/sine(c)
 * where A is the length of the side opposite angle a, etc.  The distance he has to travel, the distance your bullet 
 * has to travel, and the funny angle at the point where he is now (between the direction he's going and a straight line
 * from you to him) is enough to find the angle you need to turn your gun.  The "funny angle" (I'll call it 'ang')
 * happens to be 180+getHeading()+e.getBearing()-e.getHeading() (Except I used radians).  The distance my opponent travels
 * is enemyv*t where enemyv is his velocity and t is the amount of time before he is hit.  The distance my bullet travels is
 * bulletv*t where bulletv is calculated above.  I know from the above Law of Sines that:
 *	enemyv*t/sine(theta) = bulletv*t/sine(ang)
 *	sine(theta) = enemyv*t/(bulletv*t)*sine(ang)
 * Notice that the time is conveniently cancelled out.  "sine" is the value of sine(theta):
 */
double sine = e.getVelocity()/bulletv*Math.sin(Math.PI+getHeadingRadians()+e.getBearingRadians()-e.getHeadingRadians());
//and finally, theta is the distance I have to turn my gun:
double theta = Math.asin(sine)+getHeadingRadians()+e.getBearingRadians()-getGunHeadingRadians();
else if (theta > 0)
	turnGunRightRadians(theta);
</pre>

Of course, the weakness here is that it doesn't check walls here.  That could also be mathematically added using the third angle/side combination in the Law of cosines.  The final angle would be 180-ang-Math.abs(theta) or something, and the length of the opposite side is e.getDistance().  From there... let me see, I haven't tried this, but I'll just wing it and maybe it works:

<pre>
double finalangle = Math.PI - Math.abs(theta) - (Math.PI+getHeadingRadians()+e.getBearingRadians()-e.getHeadingRadians());
//	distance/sine(finalangle) == enemydistance/sine(theta)
double enemydistance = sine*e.getDistance()/Math.sin(finalangle);
//find their current position
double enemyStartX = getX() + e.getDistance()*Math.sin(getHeadingRadians()+e.getBearingRadians());
double enemyStartY = getY() + e.getDistance()*Math.cos(getHeadingRadians()+e.getBearingRadians());
//find their final destination
double endX = enemyStartX + enemydistance*Math.sin(e.getHeadingRadians());
double endY = enemyStartY + enemydistance*Math.cos(e.getHeadingRadians());
//figure out if they're off the screen, using offsets like David did above
if (endX < 18 || endY < 18 || endX > getBattleFieldWidth()-18 || endY > getBattleFieldHeight()-18)
{
	// now I'm going to try and find an equation for the line the opponent follows to find where it intersects with the edge.
	// finding the slope:
	double m = Math.atan(e.getHeadingRadians());
	//finding the y-intercept:
	double b = enemyStartY-enemyStartX*m;
	//now if I went off a side wall, this part is easy...
	if (endX < 18)	//plug 18 in as x (in my equation, which is in y=mx+b form)
	{
		endX = 18;
		endY = m*endX+b;
	}
	else if (endX > getBattleFieldWidth()-18)
	{
		endX = getBattleFieldWidth()-18;
		endY = m*endX+b;
	}
	//now for the top/bottom cases:
	if (endY < 18)
	{
		endY = 18;
		//now solve for x:
		endX = (endY-b)/m;
	}
	else if (endY > getBattleFieldHeight()-18)
	{
		endY = getBattleFieldHeight()-18;
		endX = (endY-b)/m;
	}
	//now adjust theta to aim at (endX, endY):
	theta = Math.atan2(endX-getX(), endY-getY())-getGunHeadingRadians();
}
//now turn the gun right theta radians and you're ready to fire!
</pre>

Lol, well, anyone can feel free to correct typos or math on that if there are mistakes, hope it's right, though.

--[[Kawigi]]

Summary:
Consciousness check: 3 * 2 =
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