public static QuadraticResult QuadraticEquation(float a, float b, float c)
{
QuadraticResult retval = new QuadraticResult();
float b4ac = b * b - 4 * a * c;
if (b4ac < 0)
{
retval.numResults = 0;
}
else if (b4ac == 0)
{
//Mathf.Sqrt(0) is 0 so ignore it
retval.numResults = 1;
retval.r1 = -b / (2 * a);
}
else
{
float sq = Mathf.Sqrt(b4ac);
retval.numResults = 2;
retval.r1 = (-b + sq) / (2 * a);
retval.r2 = (-b - sq) / (2 * a);
}
return(retval);
}
/*
* Calc time to intersect of linear moving target, given intial positions and known speed
*/
public static float CalcIntersectTime(Vector3 enemyPos, Vector3 enemyVelocity, Vector3 firingPos, float bulletSpeed)
{
//using the expanding sphere vs growing line method
//http://playtechs.blogspot.kr/2007/04/aiming-at-moving-target.html
//make local, sphere is now at origin
Vector3 dif = enemyPos - firingPos;
//squared speed dif
float a = bulletSpeed * bulletSpeed - Vector3.Dot(enemyVelocity, enemyVelocity);
//two times dot of our vector and the escape vel
float b = -2 * Vector3.Dot(enemyVelocity, dif);
float c = -Vector3.Dot(dif, dif);
QuadraticResult res = UTIL.QuadraticEquation(a, b, c);
switch (res.numResults)
{
case 1:
if (res.r1 > 0)
{
return(res.r1);
}
break;
case 2:
float max = Mathf.Max(res.r1, res.r2);
if (max > 0)
{
return(max);
}
break;
default:
break;
}
return(Mathf.Infinity);
}