Crafter.Math/interfaces/Crafter.Math-Intersection.cppm

/*
Crafter®.Math
Copyright (C) 2026 Catcrafts®
catcrafts.net

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License version 3.0 as published by the Free Software Foundation;

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
*/

export module Crafter.Math:Intersection;
import :Vector;
import std;

namespace Crafter {
    export template<typename T>
	constexpr T IntersectionTestRayTriangle(Vector<T, 3, 0> vert0, Vector<T, 3, 0> vert1, Vector<T, 3, 0> vert2, Vector<T, 3, 0> rayOrigin, Vector<T, 3, 0> rayDir) {
        Vector<T, 3, 0> edge1 = vert1 - vert0;
        Vector<T, 3, 0> edge2 = vert2 - vert0;

        Vector<T, 3, 0> h = Vector<T, 3, 0>::Cross(rayDir, edge2);
        T determinant = Vector<T, 3, 0>::Dot(edge1, h);

        if (determinant <= std::numeric_limits<T>::epsilon())  {
            return std::numeric_limits<T>::max();
        }

        T inverse_determinant = T(1) / determinant;

        Vector<T, 3, 0> origins_diff_vector = rayOrigin - vert0;
        T u =  Vector<T, 3, 0>::Dot(origins_diff_vector, h) * inverse_determinant;

        if (u < 0.0 || u > 1.0)
        {
            return std::numeric_limits<T>::max();
        }

        Vector<T, 3, 0> q = Vector<T, 3, 0>::Cross(origins_diff_vector, edge1);
        T v = inverse_determinant * Vector<T, 3, 0>::Dot(rayDir, q);

        if (v < 0.0 || u + v > 1.0) {
            return std::numeric_limits<T>::max();
        }

        return inverse_determinant * Vector<T, 3, 0>::Dot(edge2, q);
    }

    export template<typename T>
    constexpr T IntersectionTestRaySphere(Vector<T, 3, 0> position, T radius, Vector<T, 3, 0> rayOrigin, Vector<T, 3, 0> rayDir) {
        T a = Vector<T, 3, 0>::Dot(rayDir, rayDir);
        T b = Vector<T, 3, 0>::Dot(rayDir, (T(2) * (rayOrigin - position)));
        T c = Vector<T, 3, 0>::Dot(position, position) + Vector<T, 3, 0>::Dot(rayOrigin, rayOrigin) - T(2) * Vector<T, 3, 0>::Dot(rayOrigin, position) - radius * radius;
        T d = b * b + (T(-4)) * a * c;

        if (d < 0) {
            return std::numeric_limits<T>::max();
        }

        d = std::sqrt(d);

        float t = (T(-0.5)) * (b + d) / a;
        if (t > T(0)) {
            return t;
        } else {
            return std::numeric_limits<T>::max();
        }
    }

    export template<typename T>
    constexpr T IntersectionTestRayOrientedBox(Vector<T, 3, 0> boxPosition, Vector<T, 3, 0> boxSize, Vector<T, 4, 0> boxRotation, Vector<T, 3, 0> rayOrigin, Vector<T, 3, 0> rayDir) {
        Vector<T, 4, 0> invRot(
            -boxRotation.x,
            -boxRotation.y,
            -boxRotation.z,
            boxRotation.w
        );

        Vector<T, 3, 0> localOrigin = Vector<T, 3, 0>::Rotate(rayOrigin - boxPosition, invRot);
        Vector<T, 3, 0> localDir    = Vector<T, 3, 0>::Rotate(rayDir, invRot);

        Vector<T,3,0> halfExtents = boxSize * T(0.5);

        T tMin = T(0);
        T tMax = std::numeric_limits<T>::max();

        for (std::uint32_t i = 0; i < 3; ++i)
        {
            if (std::abs(localDir.v[i]) < std::numeric_limits<T>::epsilon())
            {
                if (localOrigin.v[i] < -halfExtents.v[i] || localOrigin.v[i] >  halfExtents.v[i]) {
                    return std::numeric_limits<T>::max();
                }
            }
            else
            {
                T invD = T(1) / localDir.v[i];
                T t1 = (-halfExtents.v[i] - localOrigin.v[i]) * invD;
                T t2 = ( halfExtents.v[i] - localOrigin.v[i]) * invD;

                if (t1 > t2) {
                    std::swap(t1, t2);
                }

                tMin = std::max(tMin, t1);
                tMax = std::min(tMax, t2);

                if (tMin > tMax) {
                    return std::numeric_limits<T>::max();
                }
            }
        }

        return (tMin >= T(0)) ? tMin : tMax;
    }
}