为什么我的随机数生成器不起作用

Question

检查了输出，种子生成了相同的三个数字，这很烦人。有一次，种子生成器工作正常，但它开始做同样的事情，生成相同的三个数字。在main和random_In_unit_sphere((函数中，随机数生成器每次打印相同的数字，有时会完全跳过循环。这是随机数种子。

unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();

std::mt19937 gen(seed);

std::uniform_real_distribution<float> rn1(-1.0, 1.0)

我不明白为什么会发生这种事。

// Algorithm from http://corysimon.github.io/articles/uniformdistn-on-sphere/
vecfloat random_in_unit_sphere()
{
vecfloat p(0, 0, 0);
unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();
// static std::random_device rd;
std::mt19937 gen(seed);
///Random number generator for reflections
std::uniform_real_distribution<float> rn1(-1.0, 1.0);
do
{
auto x = rn1(gen);
auto y = rn1(gen);
auto z = rn1(gen);
std::cout << "Is it working?" << std::endl;
p = ((vecfloat((float)x, (float)y, (float)z) * (float)2.0) - vecfloat(1.0f, 1.0f, 1.0f)) * 2.0;
std::cout << (double)p.squared_length() << std::endl;
} while ((double)p.squared_length() >= 1.0);
std::cout << "Is this working?" << std::endl;
return p;
}
vecfloat color(const ray &r, hittable *world)
{
hit_record rec;
//vecfloat unit_direction(0, 0, 0);
// unit_direction = unit_direction.unit_vector(r.direction());
// float t = 0.5 * (unit_direction.get_y() + 1.0);
if (world->hit(r, 0.01, __FLT_MAX__, rec))
{
vecfloat target = (rec.p + rec.normal) + random_in_unit_sphere();
//Recursive function that models real time shadows
return color(ray(rec.p, target - rec.p), world) * 0.5;
}
else
{
vecfloat unit_direction(0, 0, 0);
vecfloat get_unit_direction = unit_direction.unit_vector(r.direction());
float t = 0.5 * (get_unit_direction.get_y() + 1.0);
return vecfloat(1.0, 1.0, 1.0) * (float)(1.0 - t) + vecfloat(0.5, 0.7, 1.0) * t;
}
}
int main()
{
int nx = 200;
int ny = 100;
float ns = 100;
unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();
std::mt19937 gen(seed);
std::uniform_real_distribution<float> rn1(-1.0, 1.0);
std::ofstream out("out.ppm");
raycaster::camera cam;
out << "P3n"
<< nx << " " << ny << "n255n";
vecfloat lower_left_corner(-2.0, -1.0, -1.0);
vecfloat _horizontial(4.0, 0.0, 0.0);
vecfloat vertical(0.0, 2.0, 0.0);
vecfloat origin(0.0, 0.0, 0.0);
hittable *list[2];
vecfloat a1(0, 0, -1);
vecfloat a2(0, -100.5, -1);
list[0] = new sphere(a1, 0.5);
list[1] = new sphere(a2, 100);
hittable *world = new hittable_list(list, 2);
for (int i = ny - 1; i >= 0; i--)
{
for (int j = 0; j < nx; j++)
{
vecfloat col(0, 0, 0);
for (int s = 0; s < ns; s++)
{
auto x = rn1(gen);
auto y = rn1(gen);
float u = float(j + x) / float(nx);
float v = float(i + y) / float(ny);
// ray r(origin, (lower_left_corner + ((_horizontial * u) + (vertical * v))));
ray r = cam.get_ray(u, v);
vecfloat p = r.point_at_parameter(2.0);
col += color(r, world);
}
col /= float(ns);
col = col.squared_sides();
int ir = int(255.99 * col.get_x());
int ig = int(255.99 * col.get_y());
int ib = int(255.99 * col.get_z());
out << ir << " " << ig << " " << ib << "n";
}
}
return 0;
}

Answer 1

我太累了，看不到你的代码，但如果你想生成一个随机数，那么你应该这样做：

#include <iostream>
#include <cstdlib> // for rand() and srand()
#include <ctime> // for time()
using namespace std;
int main()
{
// initialize random number generator
srand(time(0)); // set initial seed value to system clock
// generate random number
// ...
return 0;
}

或者这个：

#include <random>
#include <iostream>
using namespace std;
int main()
{
random_device rd;   // non-deterministic generator
mt19937 gen(rd());  // to seed mersenne twister.
// replace the call to rd() with a
// constant value to get repeatable
// results.
for (int i = 0; i < 5; ++i)
{
cout << gen() << " "; // print the raw output of the generator.
}
}