C:/Doug/CSharp/XnaCollisionLib/XnaCollisionLib/Triangle.cs

Go to the documentation of this file.

using System;
using Microsoft.Xna.Framework;

namespace XnaCollisionLib
{
    public struct Triangle
    {
        public Vector3 A;
        public Vector3 B;
        public Vector3 C;
        public Plane Plane;

        public Triangle(Vector3 a, Vector3 b, Vector3 c)
        {
            A = a;
            B = b;
            C = c;
            Plane = new Plane(A, B, C);
        }

        public Triangle(Triangle triangle, Matrix transform)
        {
            A = Vector3.Transform(triangle.A, transform);
            B = Vector3.Transform(triangle.B, transform);
            C = Vector3.Transform(triangle.C, transform);
            Plane = new Plane(A, B, C);
        }

        public Nullable<float> ISect(Ray ray)
        {
            Nullable<float> t = ray.Intersects(Plane);

            if (t.HasValue && t.Value >= 0)
            {
                Vector3 point = ray.Position + t.Value * ray.Direction;

                if (!IsPointInside(point))
                    t = null;
            }
            else
                t = null;
            return t;
        }

        public bool IsFronFacing(Vector3 lookDirection)
        {
            return Vector3.Dot(Plane.Normal, lookDirection) >= 0;
        }

        public bool IsPointInside(Vector3 point)
        {
            return
                IsOnSameSide(point, A, B, C) &&
                IsOnSameSide(point, B, A, C) &&
                IsOnSameSide(point, C, A, B);
        }

        private bool IsOnSameSide(Vector3 p1, Vector3 p2, Vector3 a, Vector3 b)
        {
            Vector3 a2b = b - a;
            Vector3 cp1 = Vector3.Cross(a2b, p1 - a);
            Vector3 cp2 = Vector3.Cross(a2b, p2 - a);

            return Vector3.Dot(cp1, cp2) >= 0;
        }
    }
}