66 lines
1.8 KiB
C++
66 lines
1.8 KiB
C++
/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Copyright 2015-2018 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef __UTIL_GEOM_SPHERE_HPP
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#define __UTIL_GEOM_SPHERE_HPP
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#include "../point.hpp"
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#include "ray.hpp"
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///////////////////////////////////////////////////////////////////////////////
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namespace util::geom {
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template <size_t S, typename T>
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struct sphere {
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point<S,T> centre;
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T radius;
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};
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typedef sphere<2,float> sphere2f;
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typedef sphere<3,float> sphere3f;
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///////////////////////////////////////////////////////////////////////////
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/// returns the smallest distance from a ray to a sphere intersection
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///
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/// returns NaN on miss
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/// returns NaN if behind
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template <size_t S, typename T>
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constexpr T
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distance (const ray<S,T> r, const sphere<S,T> s)
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{
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const T b = dot (r.direction, r.origin - s.centre);
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const T c = dot (r.origin - s.centre, r.origin - s.centre) - s.radius * s.radius;
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const T D = b * b - c;
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// no intersection
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if (D < 0)
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return INFINITY;
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auto t_ = std::sqrt (D);
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auto t0 = -b + t_;
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auto t1 = -b - t_;
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return t1 >= 0 ? t1 :
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t0 >= 0 ? t0 :
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INFINITY;
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}
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}
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#endif
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