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ArborX_Ray.hpp
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ArborX_Ray.hpp
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/****************************************************************************
* Copyright (c) 2017-2022 by the ArborX authors *
* All rights reserved. *
* *
* This file is part of the ArborX library. ArborX is *
* distributed under a BSD 3-clause license. For the licensing terms see *
* the LICENSE file in the top-level directory. *
* *
* SPDX-License-Identifier: BSD-3-Clause *
****************************************************************************/
#ifndef ARBORX_RAY_HPP
#define ARBORX_RAY_HPP
#include <ArborX_Box.hpp>
#include <ArborX_DetailsAlgorithms.hpp> // equal
#include <ArborX_DetailsKokkosExtArithmeticTraits.hpp>
#include <ArborX_DetailsKokkosExtSwap.hpp>
#include <ArborX_HyperTriangle.hpp>
#include <ArborX_Point.hpp>
#include <ArborX_Sphere.hpp>
#include <Kokkos_Macros.hpp>
#if KOKKOS_VERSION >= 40200
#include <Kokkos_Assert.hpp> // KOKKOS_ASSERT
#else
#include <impl/Kokkos_Error.hpp> // KOKKOS_ASSERT
#endif
#include <cmath>
namespace ArborX::Experimental
{
struct Vector : private Point
{
using Point::Point;
using Point::operator[];
friend KOKKOS_FUNCTION constexpr bool operator==(Vector const &v,
Vector const &w)
{
return v[0] == w[0] && v[1] == w[1] && v[2] == w[2];
}
};
template <typename Point1, typename Point2>
KOKKOS_INLINE_FUNCTION constexpr std::enable_if_t<
GeometryTraits::is_point<Point1>::value &&
GeometryTraits::is_point<Point2>::value &&
GeometryTraits::dimension_v<Point1> == 3 &&
GeometryTraits::dimension_v<Point2> == 3,
Vector>
makeVector(Point1 const &begin, Point2 const &end)
{
Vector v;
for (int d = 0; d < 3; ++d)
{
v[d] = end[d] - begin[d];
}
return v;
}
KOKKOS_INLINE_FUNCTION constexpr auto dotProduct(Vector const &v,
Vector const &w)
{
return v[0] * w[0] + v[1] * w[1] + v[2] * w[2];
}
KOKKOS_INLINE_FUNCTION constexpr Vector crossProduct(Vector const &v,
Vector const &w)
{
return {v[1] * w[2] - v[2] * w[1], v[2] * w[0] - v[0] * w[2],
v[0] * w[1] - v[1] * w[0]};
}
KOKKOS_INLINE_FUNCTION constexpr bool equals(Vector const &v, Vector const &w)
{
return v == w;
}
struct Ray
{
Point _origin = {};
Vector _direction = {};
KOKKOS_DEFAULTED_FUNCTION
constexpr Ray() = default;
KOKKOS_FUNCTION
Ray(Point const &origin, Vector const &direction)
: _origin(origin)
, _direction(direction)
{
normalize(_direction);
}
KOKKOS_FUNCTION
constexpr Point &origin() { return _origin; }
KOKKOS_FUNCTION
constexpr Point const &origin() const { return _origin; }
KOKKOS_FUNCTION
constexpr Vector &direction() { return _direction; }
KOKKOS_FUNCTION
constexpr Vector const &direction() const { return _direction; }
private:
// We would like to use Scalar defined as:
// using Scalar = std::decay_t<decltype(std::declval<Vector>()[0])>;
// However, this means using float to compute the norm. This creates a large
// error in the norm that affects ray tracing for triangles. Casting the
// norm from double to float once it has been computed is not enough to
// improve the value of the normalized vector. Thus, the norm has to return a
// double.
using Scalar = double;
KOKKOS_FUNCTION
static Scalar norm(Vector const &v)
{
Scalar sq{};
for (int d = 0; d < 3; ++d)
sq += static_cast<Scalar>(v[d]) * static_cast<Scalar>(v[d]);
return std::sqrt(sq);
}
KOKKOS_FUNCTION static void normalize(Vector &v)
{
auto const magv = norm(v);
KOKKOS_ASSERT(magv > 0);
for (int d = 0; d < 3; ++d)
v[d] /= magv;
}
};
KOKKOS_INLINE_FUNCTION
constexpr bool equals(Ray const &l, Ray const &r)
{
using ArborX::Details::equals;
return equals(l.origin(), r.origin()) && equals(l.direction(), r.direction());
}
KOKKOS_INLINE_FUNCTION
Point returnCentroid(Ray const &ray) { return ray.origin(); }
// The ray-box intersection algorithm is based on [1]. Their 'efficient slag'
// algorithm checks the intersections both in front and behind the ray.
//
// There are few issues here. First, when a ray direction is aligned with one
// of the axis, a division by zero will occur. This is fine, as usually it
// results in +inf or -inf, which are treated correctly. However, it also leads
// to the second situation, when it is 0/0 which occurs when the ray's origin
// in that dimension is on the same plane as one of the corners of the box
// (i.e., if inv_ray_dir[d] == 0 && (min_corner[d] == origin[d] || max_corner[d]
// == origin[d])). This leads to NaN, which are not treated correctly (unless,
// as in [1], the underlying min/max functions are able to ignore them). The
// issue is discussed in more details in [2] and the website (key word: A
// minimal ray-tracer: rendering simple shapes).
//
// [1] Majercik, A., Crassin, C., Shirley, P., & McGuire, M. (2018). A ray-box
// intersection algorithm and efficient dynamic voxel rendering. Journal of
// Computer Graphics Techniques Vol, 7(3).
//
// [2] Williams, A., Barrus, S., Morley, R. K., & Shirley, P. (2005). An
// efficient and robust ray-box intersection algorithm. In ACM SIGGRAPH 2005
// Courses (pp. 9-es).
KOKKOS_INLINE_FUNCTION
bool intersection(Ray const &ray, Box const &box, float &tmin, float &tmax)
{
auto const &min = box.minCorner();
auto const &max = box.maxCorner();
auto const &orig = ray.origin();
auto const &dir = ray.direction();
constexpr auto inf =
Details::KokkosExt::ArithmeticTraits::infinity<float>::value;
tmin = -inf;
tmax = inf;
for (int d = 0; d < 3; ++d)
{
float tdmin;
float tdmax;
if (dir[d] >= 0)
{
tdmin = (min[d] - orig[d]) / dir[d];
tdmax = (max[d] - orig[d]) / dir[d];
}
else
{
tdmin = (max[d] - orig[d]) / dir[d];
tdmax = (min[d] - orig[d]) / dir[d];
}
if (tmin < tdmin)
tmin = tdmin;
if (tmax > tdmax)
tmax = tdmax;
}
return (tmin <= tmax);
}
KOKKOS_INLINE_FUNCTION
bool intersects(Ray const &ray, Box const &box)
{
float tmin;
float tmax;
// intersects only if box is in front of the ray
return intersection(ray, box, tmin, tmax) && (tmax >= 0.f);
}
// The function returns the index of the largest
// component of the direction vector.
KOKKOS_INLINE_FUNCTION int findLargestComp(Vector const &dir)
{
int kz = 0;
auto max = std::abs(dir[0]);
for (int i = 1; i < 3; i++)
{
auto f = std::fabs(dir[i]);
if (f > max)
{
max = f;
kz = i;
}
}
return kz;
}
// Both the ray and the triangle were transformed beforehand
// so that the ray is a unit vector along the z-axis (0,0,1),
// and the triangle is transformed with the same matrix
// (which is M in the paper). This function is called only
// when the ray is co-planar to the triangle (with the
// determinant being zero). The rotation by this function is
// to prepare for the ray-edge intersection calculations in 2D.
// The rotation is around the z-axis. For any point after
// the rotation, its new x* equals its original length
// with the correct sign, and the new y* = z. The current
// implementation avoids explicitly defining rotation angles
// and directions. The following ray-edge intersection will
// be in the x*-y* plane.
KOKKOS_INLINE_FUNCTION Point rotate2D(Point const &point)
{
Point point_star;
float r = std::sqrt(point[0] * point[0] + point[1] * point[1]);
if (point[0] != 0)
{
point_star[0] = (point[0] > 0 ? 1 : -1) * r;
}
else
{
point_star[0] = (point[1] > 0 ? 1 : -1) * r;
}
point_star[1] = point[2];
point_star[2] = 0.f;
return point_star;
}
// The function is for ray-edge intersection
// with the rotated ray along the z-axis and
// the transformed and rotated triangle edges
// The algorithm is described in
// https://en.wikipedia.org/wiki/Line%E2%80%93line_intersection#Given_two_points_on_each_line_segment
KOKKOS_INLINE_FUNCTION bool rayEdgeIntersect(Point const &edge_vertex_1,
Point const &edge_vertex_2,
float &t)
{
float x3 = edge_vertex_1[0];
float y3 = edge_vertex_1[1];
float x4 = edge_vertex_2[0];
float y4 = edge_vertex_2[1];
float y2 = std::fabs(y3) > std::fabs(y4) ? y3 : y4;
float det = y2 * (x3 - x4);
// the ray is parallel to the edge if det == 0.0
// When the ray overlaps the edge (x3==x4==0.0), it also returns false,
// and the intersection will be captured by the other two edges.
if (det == 0)
{
return false;
}
t = (x3 * y4 - x4 * y3) / det * y2;
float u = x3 * y2 / det;
auto const epsilon = 0.00001f;
return (u >= 0 - epsilon && u <= 1 + epsilon);
}
// The algorithm is described in
// Watertight Ray/Triangle Intersection
// [1] Woop, S. et al. (2013),
// Journal of Computer Graphics Techniques Vol. 2(1)
// The major difference is that here we return the intersection points
// when the ray and the triangle is coplanar.
// In the paper, they just need the boolean return.
KOKKOS_INLINE_FUNCTION
bool intersection(Ray const &ray,
ExperimentalHyperGeometry::Triangle<3> const &triangle,
float &tmin, float &tmax)
{
namespace KokkosExt = Details::KokkosExt;
auto dir = ray.direction();
// normalize the direction vector by its largest component.
auto kz = findLargestComp(dir);
int kx = (kz + 1) % 3;
int ky = (kz + 2) % 3;
if (dir[kz] < 0)
KokkosExt::swap(kx, ky);
Vector s;
s[2] = 1.0f / dir[kz];
s[0] = dir[kx] * s[2];
s[1] = dir[ky] * s[2];
// calculate vertices relative to ray origin
Vector const oA = makeVector(ray.origin(), triangle.a);
Vector const oB = makeVector(ray.origin(), triangle.b);
Vector const oC = makeVector(ray.origin(), triangle.c);
// oA, oB, oB need to be normalized, otherwise they
// will scale with the problem size.
float const mag_oA = std::sqrt(dotProduct(oA, oA));
float const mag_oB = std::sqrt(dotProduct(oB, oB));
float const mag_oC = std::sqrt(dotProduct(oC, oC));
auto mag_bar = 3.0 / (mag_oA + mag_oB + mag_oC);
Point A;
Point B;
Point C;
// perform shear and scale of vertices
// normalized by mag_bar
A[0] = (oA[kx] - s[0] * oA[kz]) * mag_bar;
A[1] = (oA[ky] - s[1] * oA[kz]) * mag_bar;
B[0] = (oB[kx] - s[0] * oB[kz]) * mag_bar;
B[1] = (oB[ky] - s[1] * oB[kz]) * mag_bar;
C[0] = (oC[kx] - s[0] * oC[kz]) * mag_bar;
C[1] = (oC[ky] - s[1] * oC[kz]) * mag_bar;
// calculate scaled barycentric coordinates
float u = C[0] * B[1] - C[1] * B[0];
float v = A[0] * C[1] - A[1] * C[0];
float w = B[0] * A[1] - B[1] * A[0];
// fallback to double precision
if (u == 0 || v == 0 || w == 0)
{
u = (double)C[0] * B[1] - (double)C[1] * B[0];
v = (double)A[0] * C[1] - (double)A[1] * C[0];
w = (double)B[0] * A[1] - (double)B[1] * A[0];
}
constexpr auto inf = KokkosExt::ArithmeticTraits::infinity<float>::value;
tmin = inf;
tmax = -inf;
// 'Back-face culling' is not supported.
// Back-facing culling is to check whether
// a surface is 'visible' to a ray, which requires
// consistent definition of the facing of triangles.
// Once the facing of triangle is defined,
// only one of the conditions is needed,
// either (u < 0 || v < 0 || w < 0) or
// (u > 0 || v > 0 || w > 0), for Back-facing culling.
float const epsilon = 0.0000001f;
if ((u < -epsilon || v < -epsilon || w < -epsilon) &&
(u > epsilon || v > epsilon || w > epsilon))
return false;
// calculate determinant
float det = u + v + w;
A[2] = s[2] * oA[kz];
B[2] = s[2] * oB[kz];
C[2] = s[2] * oC[kz];
if (det < -epsilon || det > epsilon)
{
float t = (u * A[2] + v * B[2] + w * C[2]) / det;
tmax = t;
tmin = t;
return true;
}
// The ray is co-planar to the triangle.
// Check the intersection with each edge
// the rotate2D function is to make sure the ray-edge
// intersection check is at the plane where ray and edges
// are at.
auto A_star = rotate2D(A);
auto B_star = rotate2D(B);
auto C_star = rotate2D(C);
float t_ab = inf;
bool ab_intersect = rayEdgeIntersect(A_star, B_star, t_ab);
if (ab_intersect)
{
tmin = t_ab;
tmax = t_ab;
}
float t_bc = inf;
bool bc_intersect = rayEdgeIntersect(B_star, C_star, t_bc);
if (bc_intersect)
{
tmin = KokkosExt::min(tmin, t_bc);
tmax = KokkosExt::max(tmax, t_bc);
}
float t_ca = inf;
bool ca_intersect = rayEdgeIntersect(C_star, A_star, t_ca);
if (ca_intersect)
{
tmin = KokkosExt::min(tmin, t_ca);
tmax = KokkosExt::max(tmax, t_ca);
}
if (ab_intersect || bc_intersect || ca_intersect)
{
// When (1) the origin of the ray is within the triangle
// and (2) they ray is coplanar with the triangle, the
// intersection length is zero.
if (tmin * tmax <= 0)
{
tmin = 0;
tmax = 0;
}
else
{
// need to separate tmin tmax >0 and <0 cases
// e.g., tmin = -2 and tmax = -1, but
// we want tmin = -1 and tmax = -2, when the
// ray travels backward
if (tmin < 0)
KokkosExt::swap(tmin, tmax);
}
return true;
}
return false;
} // namespace Experimental
KOKKOS_INLINE_FUNCTION bool
intersects(Ray const &ray,
ExperimentalHyperGeometry::Triangle<3> const &triangle)
{
float tmin;
float tmax;
// intersects only if triangle is in front of the ray
return intersection(ray, triangle, tmin, tmax) && (tmax >= 0.f);
}
// Returns the first positive value for t such that ray.origin + t * direction
// intersects the given box. If no such value exists, returns inf.
// Note that this definiton is different from the standard
// "smallest distance between a point on the ray and a point in the box"
// so we can use nearest queries for ray tracing.
KOKKOS_INLINE_FUNCTION
float distance(Ray const &ray, Box const &box)
{
float tmin;
float tmax;
bool intersects = intersection(ray, box, tmin, tmax) && (tmax >= 0.f);
return intersects
? (tmin > 0.f ? tmin : 0.f)
: Details::KokkosExt::ArithmeticTraits::infinity<float>::value;
}
// Solves a*x^2 + b*x + c = 0.
// If a solution exists, return true and stores roots at x1, x2.
// If a solution does not exist, returns false.
KOKKOS_INLINE_FUNCTION bool solveQuadratic(float const a, float const b,
float const c, float &x1, float &x2)
{
KOKKOS_ASSERT(a != 0);
auto const discriminant = b * b - 4 * a * c;
if (discriminant < 0)
return false;
if (discriminant == 0)
{
x1 = x2 = -b / (2 * a);
return true;
}
// Instead of doing a simple
// (-b +- std::sqrt(discriminant)) / (2*a)
// we use a more stable algorithm with less loss of precision (see, for
// clang-format off
// example, https://www.scratchapixel.com/lessons/3d-basic-rendering/minimal-ray-tracer-rendering-simple-shapes/ray-sphere-intersection).
// clang-format on
auto const q = (b > 0) ? (-b - std::sqrt(discriminant)) / 2.0
: (-b + std::sqrt(discriminant)) / 2.0;
x1 = q / a;
x2 = c / q;
return true;
}
// Ray-Sphere intersection algorithm.
//
// The sphere can be expressed as the solution to
// |p - c|^2 - r^2 = 0, (1)
// where c is the center of the sphere, and r is the radius. On the other
// hand, any point on a bidirectional ray satisfies
// p = o + t*d, (2)
// where o is the origin, and d is the direction vector.
// Substituting (2) into (1),
// |(o + t*d) - c|^2 - r^2 = 0, (3)
// results in a quadratic equation for unknown t
// a2 * t^2 + a1 * t + a0 = 0
// with
// a2 = |d|^2, a1 = 2*(d, o - c), and a0 = |o - c|^2 - r^2.
// Then, we only need to intersect the solution interval [tmin, tmax] with
// [0, +inf) for the unidirectional ray.
KOKKOS_INLINE_FUNCTION bool intersection(Ray const &ray, Sphere const &sphere,
float &tmin, float &tmax)
{
namespace KokkosExt = ArborX::Details::KokkosExt;
auto const &r = sphere.radius();
// Vector oc = (origin_of_ray - center_of_sphere)
Vector const oc = makeVector(sphere.centroid(), ray.origin());
float const a2 = 1.f; // directions are normalized
float const a1 = 2.f * dotProduct(ray.direction(), oc);
float const a0 = dotProduct(oc, oc) - r * r;
if (solveQuadratic(a2, a1, a0, tmin, tmax))
{
// ensures that tmin <= tmax
if (tmin > tmax)
KokkosExt::swap(tmin, tmax);
return true;
}
constexpr auto inf = KokkosExt::ArithmeticTraits::infinity<float>::value;
tmin = inf;
tmax = -inf;
return false;
}
template <typename Geometry>
KOKKOS_INLINE_FUNCTION void
overlapDistance(Ray const &ray, Geometry const &geometry, float &length,
float &distance_to_origin)
{
namespace KokkosExt = ArborX::Details::KokkosExt;
float tmin;
float tmax;
if (intersection(ray, geometry, tmin, tmax) && (tmin <= tmax && tmax >= 0))
{
// Overlap [tmin, tmax] with [0, +inf)
tmin = KokkosExt::max(0.f, tmin);
// As direction is normalized,
// |(o + tmax*d) - (o + tmin*d)| = tmax - tmin
length = tmax - tmin;
distance_to_origin = tmin;
}
else
{
length = 0;
distance_to_origin = KokkosExt::ArithmeticTraits::infinity<float>::value;
}
}
KOKKOS_INLINE_FUNCTION float overlapDistance(Ray const &ray,
Sphere const &sphere)
{
float distance_to_origin;
float length;
overlapDistance(ray, sphere, length, distance_to_origin);
return length;
}
} // namespace ArborX::Experimental
template <>
struct ArborX::GeometryTraits::dimension<ArborX::Experimental::Ray>
{
static constexpr int value = 3;
};
template <>
struct ArborX::GeometryTraits::tag<ArborX::Experimental::Ray>
{
using type = RayTag;
};
template <>
struct ArborX::GeometryTraits::coordinate_type<ArborX::Experimental::Ray>
{
using type = float;
};
#endif