text: // Copyright (C) 2002-2012 Nikolaus Gebhardt
  // This file is part of the "Irrlicht Engine".
  // For conditions of distribution and use, see copyright notice in irrlicht.h
  
  #ifndef __IRR_LINE_3D_H_INCLUDED__
  #define __IRR_LINE_3D_H_INCLUDED__
  
  #include "irrTypes.h"
  #include "vector3d.h"
  
  namespace irr
  {
  namespace core
  {
  
  //! 3D line between two points with intersection methods.
  template <class T>
  class line3d
  {
  	public:
  
  		//! Default constructor
  		/** line from (0,0,0) to (1,1,1) */
  		line3d() : start(0,0,0), end(1,1,1) {}
  		//! Constructor with two points
  		line3d(T xa, T ya, T za, T xb, T yb, T zb) : start(xa, ya, za), end(xb, yb, zb) {}
  		//! Constructor with two points as vectors
  		line3d(const vector3d<T>& start, const vector3d<T>& end) : start(start), end(end) {}
  
  		// operators
  
  		line3d<T> operator+(const vector3d<T>& point) const { return line3d<T>(start + point, end + point); }
  		line3d<T>& operator+=(const vector3d<T>& point) { start += point; end += point; return *this; }
  
  		line3d<T> operator-(const vector3d<T>& point) const { return line3d<T>(start - point, end - point); }
  		line3d<T>& operator-=(const vector3d<T>& point) { start -= point; end -= point; return *this; }
  
  		bool operator==(const line3d<T>& other) const
  		{ return (start==other.start && end==other.end) || (end==other.start && start==other.end);}
  		bool operator!=(const line3d<T>& other) const
  		{ return !(start==other.start && end==other.end) || (end==other.start && start==other.end);}
  
  		// functions
  		//! Set this line to a new line going through the two points.
  		void setLine(const T& xa, const T& ya, const T& za, const T& xb, const T& yb, const T& zb)
  		{start.set(xa, ya, za); end.set(xb, yb, zb);}
  		//! Set this line to a new line going through the two points.
  		void setLine(const vector3d<T>& nstart, const vector3d<T>& nend)
  		{start.set(nstart); end.set(nend);}
  		//! Set this line to new line given as parameter.
  		void setLine(const line3d<T>& line)
  		{start.set(line.start); end.set(line.end);}
  
  		//! Get length of line
  		/** \return Length of line. */
  		T getLength() const { return start.getDistanceFrom(end); }
  
  		//! Get squared length of line
  		/** \return Squared length of line. */
  		T getLengthSQ() const { return start.getDistanceFromSQ(end); }
  
  		//! Get middle of line
  		/** \return Center of line. */
  		vector3d<T> getMiddle() const
  		{
  			return (start + end)/(T)2;
  		}
  
  		//! Get vector of line
  		/** \return vector of line. */
  		vector3d<T> getVector() const
  		{
  			return end - start;
  		}
  
  		//! Check if the given point is between start and end of the line.
  		/** Assumes that the point is already somewhere on the line.
  		\param point The point to test.
  		\return True if point is on the line between start and end, else false.
  		*/
  		bool isPointBetweenStartAndEnd(const vector3d<T>& point) const
  		{
  			return point.isBetweenPoints(start, end);
  		}
  
  		//! Get the closest point on this line to a point
  		/** \param point The point to compare to.
  		\return The nearest point which is part of the line. */
  		vector3d<T> getClosestPoint(const vector3d<T>& point) const
  		{
  			vector3d<T> c = point - start;
  			vector3d<T> v = end - start;
  			T d = (T)v.getLength();
  			v /= d;
  			T t = v.dotProduct(c);
  
  			if (t < (T)0.0)
  				return start;
  			if (t > d)
  				return end;
  
  			v *= t;
  			return start + v;
  		}
  
  		//! Check if the line intersects with a sphere
  		/** \param sorigin: Origin of the sphere.
  		\param sradius: Radius of the sphere.
  		\param outdistance: The distance to the first intersection point.
  		\return True if there is an intersection.
  		If there is one, the distance to the first intersection point
  		is stored in outdistance. */
  		bool getIntersectionWithSphere(const vector3d<T>& sorigin, T sradius, f64& outdistance) const
  		{
  			const vector3d<T> q = sorigin - start;
  			T c = q.getLength();
  			T v = q.dotProduct(getVector().normalize());
  			T d = sradius * sradius - (c*c - v*v);
  
  			if (d < 0.0)
  				return false;
  
  			outdistance = v - core::squareroot ( d );
  			return true;
  		}
  
  		// member variables
  
  		//! Start point of line
  		vector3d<T> start;
  		//! End point of line
  		vector3d<T> end;
  };
  
  	//! Typedef for an f32 line.
  	typedef line3d<f32> line3df;
  	//! Typedef for an integer line.
  	typedef line3d<s32> line3di;
  
  } // end namespace core
  } // end namespace irr
  
  #endif
  
  