55 lines
1.4 KiB
C++
55 lines
1.4 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2015-2018 Danny Robson <danny@nerdcruft.net>
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*/
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#pragma once
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#include "../point.hpp"
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#include "ray.hpp"
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///////////////////////////////////////////////////////////////////////////////
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namespace cruft::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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