distance.h

#pragma once
 
#include "fvec.h"
 
namespace cgv {
namespace math {
 
template <typename T>
T point_box_distance(const fvec<T, 3>& point, fvec<T, 3> extent) {
 
    fvec<T, 3> q = abs(point) - T(0.5) * extent;
    return length(max(q, T(0))) + std::min(std::max(q.x(), std::max(q.y(), q.z())), T(0));
}
 
template <typename T>
T point_plane_distance(const fvec<T, 3>& point, const fvec<T, 3>& origin, const fvec<T, 3>& normal) {
 
    return dot(point - origin, normal);
};
 
template <typename T, cgv::type::uint32_type N>
T point_sphere_distance(const fvec<T, N>& point, const fvec<T, N>& center, T radius) {
 
    return length(center - point) - radius;
}
 
template<typename T>
static std::pair<T, T> point_quadratic_bezier_distance(const fvec<T, 3>& point, const fvec<T, 3>& p0, const fvec<T, 3>& p1, const fvec<T, 3>& p2) {
    // (Copyright 2013 Inigo Quilez: https://iquilezles.org/articles/bezierbbox/ and https://www.shadertoy.com/view/ldj3Wh)
    using vec_type = fvec<T, 3>;
    vec_type a = p1 - p0;
    vec_type b = p0 - T(2) * p1 + p2;
    vec_type c = a * T(2);
    vec_type d = p0 - point;
 
    T kk = T(1) / dot(b, b);
    T kx = kk * dot(a, b);
    T ky = kk * (T(2) * dot(a, a) + dot(d, b)) / T(3);
    T kz = kk * dot(d, a);
 
    T dist = T(0);
    T t = T(0);
 
    T p = ky - kx * kx;
    T p3 = p * p * p;
    T q = kx * (T(2) * kx * kx - T(3) * ky) + kz;
    T h = q * q + T(4) * p3;
 
    if(h >= T(0)) {
        h = std::sqrt(h);
        fvec<T, 2> x = (vec2(h, -h) - q) / T(2);
        fvec<T, 2> uv = sign(x) * pow(abs(x), vec2(T(1) / T(3)));
        t = clamp(uv.x() + uv.y() - kx, T(0), T(1));
 
        // 1 root
        dist = sqr_length(d + (c + b * t) * t);
    } else {
        T z = std::sqrt(-p);
        T v = std::acos(q / (p * z * T(2))) / T(3);
        T m = std::cos(v);
        T n = std::sin(v) * T(1.732050808);
        vec_type ts = clamp(vec_type(m + m, -n - m, n - m) * z - kx, T(0), T(1));
 
        // 3 roots, but only need two
        T dt = sqr_length(d + (c + b * ts.x()) * ts.x());
        dist = dt;
        t = ts.x();
 
        dt = sqr_length(d + (c + b * ts.y()) * ts.y());
        if(dt < dist) {
            dist = dt;
            t = ts.y();
        }
    }
 
    dist = sqrt(dist);
 
    return { dist, t };
}
 
} // namespace math
} // namespace cgv