// Same as above, but avoid using Sqrt(), saves a new nanoseconds in cases where you only want
// to compare several distances to find the smallest or largest, but don't need the distance
public static float DistanceToLineSegmentSquared(Vector2 A, Vector2 B, Vector2 P, out Vector2 closestPoint)
{
// Compute length of line segment (squared) and handle special case of coincident points
float segmentLengthSquared = A.SqrDist(B);
if (segmentLengthSquared < 1E-7f) // Arbitrary "close enough for government work" value
{
closestPoint = A;
return P.SqrDist(closestPoint);
}
// Use the magic formula to compute the "projection" of this point on the infinite line
Vector2 lineSegment = B - A;
float t = Vector2.Dot(P - A, lineSegment) / segmentLengthSquared;
// Handle the two cases where the projection is not on the line segment, and the case where
// the projection is on the segment
if (t <= 0)
closestPoint = A;
else if (t >= 1)
closestPoint = B;
else
closestPoint = A + (lineSegment * t);
return P.SqrDist(closestPoint);
}