/*
 * 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) {
            // find the distance to the point, if it's positive it's inside
            // the frustum.
            const auto d = max (
                p.coefficients * b.lo.template redim<S+1> (1),
                p.coefficients * b.hi.template redim<S+1> (1)
            );

            if (sum (d) < 0)
                return false;
        }

        return true;
    }
};

#endif