libcruft-util/geom/segment.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2018 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include "../point.hpp"


namespace cruft::geom {
    template <size_t S, typename T>
    struct segment {
        cruft::point<S,T> a;
        cruft::point<S,T> b;
    };


    using segment2f = segment<2,float>;
    using segment3f = segment<3,float>;


    template <size_t S, typename T>
    T
    distance2 (segment<S,T> s, point<S,T> p)
    {
        const auto dir = s.b - s.a;
        const auto t1 = dot (p - s.a, dir);
        if (t1 < 0)
            return distance2 (p, s.a);

        const auto t2 = dot (dir, dir);
        if (t2 < t1)
            return distance2 (p, s.b);

        auto t = t1 / t2;
        return distance2 (p, s.a + t * dir);
    }


    template <size_t S, typename T>
    T
    distance (segment<S,T> s, point<S,T> p)
    {
        return std::sqrt (distance2 (s, p));
    }
};