libcruft-util/cruft/util/geom/aabb.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 2015-2018 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include "../debug/assert.hpp"
#include "../extent.hpp"
#include "../point.hpp"


namespace cruft::geom {
    ///////////////////////////////////////////////////////////////////////////
    /// represents an axis-aligned bounding-box through two opposing corners.
    ///
    /// `lo' must be less-than-or-equal to `hi'. equality is allowed so that
    /// we can represent zero sized bounding-boxes.
    template <size_t S, typename T>
    struct aabb {
        using point_type = cruft::point<S,T>;

        aabb () = default;
        aabb (point<S,T> _lo, point<S,T> _hi):
            lo (_lo),
            hi (_hi)
        {
            CHECK (all (lo <= hi));
        }


        ///////////////////////////////////////////////////////////////////////
        /// Returns a copy of the AABB with all elements implicitly cast to the
        /// type `DestinationT`.
        template <typename DestinationT>
        constexpr aabb<S, DestinationT>
        cast (void) const
        {
            return {
                lo.template cast<DestinationT> (),
                hi.template cast<DestinationT> ()
            };
        }


        ///////////////////////////////////////////////////////////////////////
        extent<S,T>
        magnitude (void) const
        {
            return (hi - lo).template as<cruft::extent> ();
        }


        ///--------------------------------------------------------------------
        T
        diameter (void) const
        {
            return magnitude ().diameter ();
        }


        //---------------------------------------------------------------------
        point<S,T>
        centre (void) const
        {
            point<S,T> res;
            for (std::size_t i = 0; i < S; ++i)
                res[i] = (lo[i] + hi[i]) / 2;
            return res;
        }


        ///--------------------------------------------------------------------
        /// tests whether a point lies within the region, inclusive of borders
        constexpr bool
        inclusive (point<S,T> p) const noexcept
        { return all (lo <= p && hi >= p); }


        ///--------------------------------------------------------------------
        /// Find's the closest point on the AABB border to the supplied point.
        point<S,T>
        closest (point<S,T> query) const
        {
            return clamp (query, lo, hi);
        }


        ///--------------------------------------------------------------------
        /// Modifies the AABB to cover the supplied point inclusively.
        void cover (point<S,T> p)
        {
            lo = min (p, lo);
            hi = max (p, hi);
        }


        ///////////////////////////////////////////////////////////////////////
        /// Applies a negative offset to lo, and a positive offset to hi, and
        /// returns the result.
        ///
        /// The offset applied is identical for lo and hi, so one may need to
        /// consider halving the supplied magnitude depending on the use case.
        aabb<S,T>
        expand [[nodiscard]] (T mag) const
        {
            return {
                lo - mag,
                hi + mag
            };
        }

        ///////////////////////////////////////////////////////////////////////
        /// Adds a constant vector to both the lo and hi points.
        aabb<S,T> operator+ (vector<S,T> v) const
        {
            return { lo + v, hi + v };
        }


        ///--------------------------------------------------------------------
        /// Substracts a constant vector from both the lo and hi points.
        aabb<S,T> operator- (vector<S,T> v) const
        {
            return { lo - v, hi - v };
        }


        ///////////////////////////////////////////////////////////////////////
        /// Returns an aabb that covers the supplied point in addition to the
        /// current aabb area.
        auto operator| [[nodiscard]] (point<S,T> p) const noexcept
        {
            return aabb (
                cruft::min (lo, p),
                cruft::max (hi, p)
            );
        }


        ///--------------------------------------------------------------------
        /// Modifies the AABB to cover the supplied point inclusively.
        auto& operator|= (point<S,T> p) noexcept
        {
            return *this = *this | p;
        }


        ///--------------------------------------------------------------------
        /// Returns an AABB that covers this AABB and the supplied AABB.
        aabb operator| [[nodiscard]] (aabb<S,T> rhs) const noexcept
        {
            return {
                min (lo, rhs.lo),
                max (hi, rhs.hi)
            };
        }


        ///--------------------------------------------------------------------
        /// Returns a read only list of vertices for the AABB.
        std::array<cruft::point<S,T>,cruft::pow(2,S)>
        vertices (void) const noexcept;


        ///////////////////////////////////////////////////////////////////////
        /// The most negative corner of the AABB.
        ::cruft::point<S,T> lo;

        /// The most positive corner of the AABB.
        ::cruft::point<S,T> hi;
    };


    ///////////////////////////////////////////////////////////////////////////
    template <std::size_t S, typename T>
    constexpr bool
    operator== (const aabb<S,T> &a, const aabb<S,T> &b) noexcept
    {
        return a.lo == b.lo && a.hi == b.hi;
    }


    ///////////////////////////////////////////////////////////////////////////
    typedef aabb<2,float> aabb2f;
    typedef aabb<2,unsigned> aabb2u;
    typedef aabb<2,int> aabb2i;

    typedef aabb<3,float> aabb3f;
    typedef aabb<3,unsigned> aabb3u;
    typedef aabb<3,int> aabb3i;


    template <size_t S, typename T>
    bool
    intersects (aabb<S,T> const &a, point<S,T> const &b) noexcept
    {
        return a.inclusive (b);
    }


    ///////////////////////////////////////////////////////////////////////////
    /// Returns the squared minimum distance from the AABB to a point.
    template <size_t S, typename T>
    T distance2 (aabb<S,T> a, point<S,T> b);


    //-------------------------------------------------------------------------
    template <size_t S, typename T>
    T
    distance2 (point<S,T> a, aabb<S,T> b)
    {
        return distance2 (b, a);
    }
}


///////////////////////////////////////////////////////////////////////////////
#include "sample/fwd.hpp"

#include <random>

namespace cruft::geom::sample {
    template <size_t S, typename T>
    class volume<aabb<S,T>> {
    public:
        using shape_type = aabb<S,T>;

        volume (shape_type&&);
        volume (shape_type const &target):
            m_target (target)
        { ; }


        template <typename GeneratorT>
        auto
        eval (GeneratorT &&g) const noexcept
        {
            point<S,T> res;

            for (size_t i = 0; i < S; ++i)
                res[i] = cruft::random::uniform (m_target.lo[i], m_target.hi[i], g);

            return res;
        }


    private:
        shape_type const &m_target;
    };
}