libcruft-util/ray.cpp

/*
 * 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 2015 Danny Robson <danny@nerdcruft.net>
 */

#include "ray.hpp"

#include "debug.hpp"


//-----------------------------------------------------------------------------
template <size_t S, typename T>
util::ray<S,T>::ray (util::point<S,T> _p,
                       util::vector<S,T> _d):
    p (_p),
    d (_d)
{
    CHECK_EQ (d.magnitude2 (), 1);
}


///----------------------------------------------------------------------------
/// returns the distance along the ray in a ray-plane intersection
///
/// returns inf if parallel
/// returns 0   if corayar
template <size_t S, typename T>
T
util::ray<S,T>::intersect (plane<S,T> q) const
{
    return dot (q.p - p, q.n) / dot (d, q.n);
}


///----------------------------------------------------------------------------
/// returns the distance from origin to AABB intersection
///
/// returns NaN on miss
/// returns -ve if behind
template <size_t S, typename T>
T
util::ray<S,T>::intersect (AABB<S,T> r) const
{
    auto t1 = (r.p0 - p) / d;
    auto t2 = (r.p1 - p) / d;

    auto vmin = min (t1, t2);
    auto vmax = max (t1, t2);

    auto tmin = max (vmin);
    auto tmax = min (vmax);

    if (tmax < 0)
        return tmax;

    if (tmin > tmax)
        return std::numeric_limits<T>::quiet_NaN ();

    return tmin;
}


///----------------------------------------------------------------------------
/// returns the smallest distance from ray origin to a sphere intersection
///
/// returns NaN on miss
template <size_t S, typename T>
T
util::ray<S,T>::intersect (sphere<S,T> s) const
{
    T b = dot (d, p - s.c);
    T c = dot (p - s.c, p - s.c) - s.r * s.r;

    T D = b * b - c;
    if (D < 0)
        return std::numeric_limits<T>::quiet_NaN ();

    auto t_ = std::sqrt (D);
    auto t0 = -b + t_;
    auto t1 = -b - t_;

    return t1 >= 0 ? t1 :
           t0 >= 0 ? t0 :
           std::numeric_limits<T>::quiet_NaN ();
}


///----------------------------------------------------------------------------
/// returns the closest parameter along the ray to a given point
template <size_t S, typename T>
T
util::ray<S,T>::closest (point<S,T> q) const
{
    // project the origin-point difference onto the direction
    return dot (p - q, d);
}


//-----------------------------------------------------------------------------
template <size_t S, typename T>
util::point<S,T>
util::ray<S,T>::at (T t) const
{
    return p + d * t;
}


//-----------------------------------------------------------------------------
template struct util::ray<2,float>;
template struct util::ray<3,float>;