BansheeEngine/BansheeUtility/Source/BsLineSegment3.cpp

#include "BsLineSegment3.h"
#include "BsRay.h"

namespace BansheeEngine
{
	LineSegment3::LineSegment3(const Vector3& start, const Vector3& end)
		:mStart(start), mEnd(end)
	{ 

	}

	std::pair<std::array<Vector3, 2>, float>  LineSegment3::getNearestPoint(const Ray& ray) const
	{
		const Vector3& org = ray.getOrigin();
		const Vector3& dir = ray.getDirection();

		Vector3 segDir = mEnd - mStart;
		float segExtent = segDir.normalize() * 0.5f;
		Vector3 segCenter = mStart + segDir * segExtent;

		Vector3 diff = org - segCenter;
		float a01 = -dir.dot(segDir);
		float b0 = diff.dot(dir);
		float c = diff.dot(diff);
		float det = fabs(1.0f - a01*a01);

		float s0, s1;
		float sqrDistance;
		if (det > 0.0f) // Not parallel
		{
			
			float b1 = -diff.dot(segDir);
			s1 = a01 * b0 - b1;
			float extDet = segExtent * det;

			if (s1 >= -extDet)
			{
				if (s1 <= extDet) // Interior of the segment and interior of the ray are closest
				{
					float invDet = 1.0f / det;
					s0 = (a01*b1 - b0)*invDet;
					s1 *= invDet;

					sqrDistance = s0*(s0 + a01*s1 + 2.0f*b0) +
						s1*(a01*s0 + s1 + 2.0f*b1) + c;
				}
				else // Segment end and interior of the ray are closest
				{
					s1 = segExtent;
					s0 = -(a01*s1 + b0);
					sqrDistance = -s0*s0 + s1*(s1 + (2.0f)*b1) + c;
				}
			}
			else // Segment start and interior of the ray are closest
			{
				s1 = -segExtent;
				s0 = -(a01*s1 + b0);
				sqrDistance = -s0*s0 + s1*(s1 + (2.0f)*b1) + c;
			}
		}
		else // Parallel
		{
			s1 = 0;
			s0 = -b0;
			sqrDistance = b0*s0 + c;
		}

		if (sqrDistance < 0.0f)
			sqrDistance = 0.0f;

		float distance = std::sqrt(sqrDistance);

		std::array<Vector3, 2> nearestPoints;
		nearestPoints[0] = org + s0 * dir;
		nearestPoints[1] = segCenter + s1 * segDir;

		return std::make_pair(nearestPoints, distance);
	}
}