overlaps_plane_triangle.h

// Description: Overlap tests between a plane and a triangle

#ifndef PASTELGEOMETRY_OVERLAPS_PLANE_TRIANGLE_H
#define PASTELGEOMETRY_OVERLAPS_PLANE_TRIANGLE_H

#include "pastel/geometry/shape/plane.h"
#include "pastel/geometry/shape/triangle.h"
#include "pastel/sys/mytypes.h"

namespace Pastel
{

    //! Tests if a plane and a triangle overlap.
    /*!
   The triangle is considered to be closed and solid.
   */
    template <typename Real, int N>
        bool overlaps(
            const Plane<Real, N> &plane,
            const PASTEL_TRIANGLE(Real, N) &triangle)
    {
        // A triangle overlaps the plane
        // if there is a triangle point
        // that is on the plane or
        // there exists two triangle points
        // that are on the opposite sides
        // of the plane.

        Real d1(dot(plane.normal(),
            triangle[0] - plane.position()));

        // EPSILON
        if (d1 == 0)
        {
            // A vertex is on the plane,
            // thus the triangle intersects it.

            return true;
        }

        Real d2(dot(plane.normal(),
            triangle[1] - plane.position()));

        // EPSILON
        if (d2 == 0)
        {
            // A vertex is on the plane,
            // thus the triangle intersects it.

            return true;
        }

        Real d3(dot(plane.normal(),
            triangle[2] - plane.position()));

        // EPSILON
        if (d3 == 0)
        {
            // A vertex is on the plane,
            // thus the triangle intersects it.

            return true;
        }

        bool aSide = d1 > 0;
        bool bSide = d2 > 0;
        bool cSide = d3 > 0;

        return ((aSide != bSide) || (aSide != cSide));
    }

}

#endif