Free, commercially distributable, modifiable, open source code. This class is part of the XnaGeometry library, a 3d library. To download the entire XnaGeometry library, click here. XnaGeometry uses the same function names as XNA so you can use the Microsoft XNA documentation. XnaGeometry will allow you to decouple your calculations from the renderer, and uses doubles for precision. Monogame has rendering support.

#region License
/*
MIT License
Copyright © 2006 The Mono.Xna Team


All rights reserved.


Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:


The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.


THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/
#endregion License


using System;
using System.ComponentModel;
#if WINRT
using System.Runtime.Serialization;
#endif


namespace XnaGeometry
{
#if WINRT
    [DataContract]
#else
    [Serializable]
#endif
    public struct Ray : IEquatable<Ray>
    {
        #region Public Fields
#if WINRT
        [DataMember]
#endif
        public Vector3 Direction;
#if WINRT
        [DataMember]
#endif
        public Vector3 Position;


        #endregion




        #region Public Constructors


        public Ray(Vector3 position, Vector3 direction)
        {
            this.Position = position;
            this.Direction = direction;
        }


        #endregion




        #region Public Methods


        public override bool Equals(object obj)
        {
            return (obj is Ray) ? this.Equals((Ray)obj) : false;
        }



        public bool Equals(Ray other)
        {
            return this.Position.Equals(other.Position) && this.Direction.Equals(other.Direction);
        }



        public override int GetHashCode()
        {
            return Position.GetHashCode() ^ Direction.GetHashCode();
        }



        public double? Intersects(BoundingBox box)
        {
            //first test if start in box
            if (Position.X >= box.Min.X
                && Position.X <= box.Max.X
                && Position.Y >= box.Min.Y
                && Position.Y <= box.Max.Y
                && Position.Z >= box.Min.Z
                && Position.Z <= box.Max.Z)
                return 0.0f;// here we concidere cube is full and origine is in cube so intersect at origine


            //Second we check each face
            Vector3 maxT = new Vector3(-1.0f);
            //Vector3 minT = new Vector3(-1.0f);
            //calcul intersection with each faces
            if (Position.X < box.Min.X && Direction.X != 0.0f)
                maxT.X = (box.Min.X - Position.X) / Direction.X;
            else if (Position.X > box.Max.X && Direction.X != 0.0f)
                maxT.X = (box.Max.X - Position.X) / Direction.X;
            if (Position.Y < box.Min.Y && Direction.Y != 0.0f)
                maxT.Y = (box.Min.Y - Position.Y) / Direction.Y;
            else if (Position.Y > box.Max.Y && Direction.Y != 0.0f)
                maxT.Y = (box.Max.Y - Position.Y) / Direction.Y;
            if (Position.Z < box.Min.Z && Direction.Z != 0.0f)
                maxT.Z = (box.Min.Z - Position.Z) / Direction.Z;
            else if (Position.Z > box.Max.Z && Direction.Z != 0.0f)
                maxT.Z = (box.Max.Z - Position.Z) / Direction.Z;


            //get the maximum maxT
            if (maxT.X > maxT.Y && maxT.X > maxT.Z)
            {
                if (maxT.X < 0.0f)
                    return null;// ray go on opposite of face
                //coordonate of hit point of face of cube
                double coord = Position.Z + maxT.X * Direction.Z;
                // if hit point coord ( intersect face with ray) is out of other plane coord it miss 
                if (coord < box.Min.Z || coord > box.Max.Z)
                    return null;
                coord = Position.Y + maxT.X * Direction.Y;
                if (coord < box.Min.Y || coord > box.Max.Y)
                    return null;
                return maxT.X;
            }
            if (maxT.Y > maxT.X && maxT.Y > maxT.Z)
            {
                if (maxT.Y < 0.0f)
                    return null;// ray go on opposite of face
                //coordonate of hit point of face of cube
                double coord = Position.Z + maxT.Y * Direction.Z;
                // if hit point coord ( intersect face with ray) is out of other plane coord it miss 
                if (coord < box.Min.Z || coord > box.Max.Z)
                    return null;
                coord = Position.X + maxT.Y * Direction.X;
                if (coord < box.Min.X || coord > box.Max.X)
                    return null;
                return maxT.Y;
            }
            else //Z
            {
                if (maxT.Z < 0.0f)
                    return null;// ray go on opposite of face
                //coordonate of hit point of face of cube
                double coord = Position.X + maxT.Z * Direction.X;
                // if hit point coord ( intersect face with ray) is out of other plane coord it miss 
                if (coord < box.Min.X || coord > box.Max.X)
                    return null;
                coord = Position.Y + maxT.Z * Direction.Y;
                if (coord < box.Min.Y || coord > box.Max.Y)
                    return null;
                return maxT.Z;
            }
        }




        public void Intersects(ref BoundingBox box, out double? result)
        {
            result = Intersects(box);
        }




        public double? Intersects(BoundingFrustum frustum)
        {
            if (frustum == null)
            {
                throw new ArgumentNullException("frustum");
            }


            return frustum.Intersects(this);


        }




        public double? Intersects(BoundingSphere sphere)
        {
            double? result;
            Intersects(ref sphere, out result);
            return result;
        }


        public double? Intersects(Plane plane)
        {
            double? result;
            Intersects(ref plane, out result);
            return result;
        }


        public void Intersects(ref Plane plane, out double? result)
        {
            var den = Vector3.Dot(Direction, plane.Normal);
            if (Math.Abs(den) < 0.00001f)
            {
                result = null;
                return;
            }


            result = (-plane.D - Vector3.Dot(plane.Normal, Position)) / den;


            if (result < 0.0f)
            {
                if (result < -0.00001f)
                {
                    result = null;
                    return;
                }


                result = 0.0f;
            }
        }


        public void Intersects(ref BoundingSphere sphere, out double? result)
        {
            // Find the vector between where the ray starts the the sphere's centre
            Vector3 difference = sphere.Center - this.Position;


            double differenceLengthSquared = difference.LengthSquared();
            double sphereRadiusSquared = sphere.Radius * sphere.Radius;


            double distanceAlongRay;


            // If the distance between the ray start and the sphere's centre is less than
            // the radius of the sphere, it means we've intersected. N.B. checking the LengthSquared is faster.
            if (differenceLengthSquared < sphereRadiusSquared)
            {
                result = 0.0f;
                return;
            }


            Vector3.Dot(ref this.Direction, ref difference, out distanceAlongRay);
            // If the ray is pointing away from the sphere then we don't ever intersect
            if (distanceAlongRay < 0)
            {
                result = null;
                return;
            }


            // Next we kinda use Pythagoras to check if we are within the bounds of the sphere
            // if x = radius of sphere
            // if y = distance between ray position and sphere centre
            // if z = the distance we've travelled along the ray
            // if x^2 + z^2 - y^2 < 0, we do not intersect
            double dist = sphereRadiusSquared + distanceAlongRay * distanceAlongRay - differenceLengthSquared;


            result = (dist < 0) ? null : distanceAlongRay - (double?)Math.Sqrt(dist);
        }




        public static bool operator !=(Ray a, Ray b)
        {
            return !a.Equals(b);
        }




        public static bool operator ==(Ray a, Ray b)
        {
            return a.Equals(b);
        }




        public override string ToString()
        {
            return string.Format("{{Position:{0} Direction:{1}}}", Position.ToString(), Direction.ToString());
        }


        #endregion
    }
}