/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Copyright 2018 Danny Robson <danny@nerdcruft.net>
 */

#ifndef CRUFT_UTIL_GEOM_FRUSTUM_HPP
#define CRUFT_UTIL_GEOM_FRUSTUM_HPP

#include "../matrix.hpp"
#include "plane.hpp"
#include "aabb.hpp"

#include <array>

#include <cstddef>

namespace util::geom {
    /// a viewing frustrum comprised of 4 axis planes, a near plane, and a far
    /// plane. it may describe something other than a perspective projection
    /// (eg, an orthographic projection)
    template <typename ValueT>
    struct frustum {
        explicit frustum (const matrix<4,4,ValueT>&);

        std::array<plane<3,ValueT>, 6> planes;
    };

    using frustum3f = frustum<float>;


    /// tests whether a frustum and an aabb overlap
    ///
    /// XXX: there may be occasional false positives.
    template <size_t S, typename T>
    bool
    intersects (const frustum<T> &f, const aabb<S,T> &b)
    {
        for (const auto &p: f.planes) {
            const auto n = normal (p);
            const auto positive = n > 0;

            const auto lo = select (positive, b.lo, b.hi);
            const auto hi = select (positive, b.hi, b.lo);

            if (dot (n, lo) + p.coefficients[S] > 0)
                return false; // OUTSIDE

            if (dot (n, hi) + p.coefficients[S] >= 0)
                return true; //INTERSECT
        }

        // INSIDE
        return true;
    }
};

#endif