public static HitResult?TryHit(this IProjectileCollider collider, Ray ray)
{
var start = ray.Start.NumericValue;
var dir = ray.Direction.NumericValue;
var center = collider.Position.NumericValue;
var radius = collider.Radius.NumericValue;
var a = start.X - center.X;
var b = start.Y - center.Y;
var r2 = radius * radius;
var c2 = dir.X * dir.X;
var d2 = dir.Y * dir.Y;
var cd = dir.X * dir.Y;
var s = (r2 - a * a) * d2
+ (r2 - b * b) * c2
+ 2 * a * b * cd;
// if s is less than 0, the solutions for f are imaginary
// and the ray's line does not intersect the circle
if (s >= 0)
{
var f = (Mathf.Sqrt(s) + a * dir.X + b * dir.Y) / -(c2 + d2);
if (f <= 1)
{
var isInside = a * a + b * b < r2;
if (f >= 0 || (isInside && !float.IsNegativeInfinity(f)))
{
// TODO: currently returns negative f if ray starts inside
// consider treating this case differently?
// do we ever care about 'exit hits'?
// probably want to split entry/exit hits
// how to handle moving targets?
return(new HitResult(
new Position2(start + dir * f),
Direction2.Of(new Vector2(a, b)),
f,
isInside
));
}
}
}
return(null);
}
/// <summary>
/// Converts an Euclidean position into polar coordinates.
/// </summary>
/// <param name="position">The Euclidean representation of the point.</param>
/// <returns>The polar representation of the specified point.</returns>
public static PolarPosition FromVector2(Vector2 position)
{
return(new PolarPosition(position.Length, Direction2.Of(position)));
}