random.cpp

#include "common.h"

Vector2f disk_sample() {
    Vector2f u(next_float(), next_float());
    u = 2.f*u - Vector2f(1, 1);

    if (u.x == 0 && u.y == 0)
        return Vector2f(0,0);
    
    float theta, r;
    if (std::abs(u.x) > std::abs(u.y))
    {
        r = u.x;
        theta = M_PI4 * (u.y/u.x);
    } else {
        r = u.y;
        theta = M_PI2 - M_PI4 * (u.x/u.y);
    }

    return r*Vector2f(std::cos(theta), std::sin(theta));
}

Vector3f cosine_hemisphere() {
    Vector2f d = disk_sample();
    float z = std::sqrt(std::max((float)0, 1 - d.x*d.x - d.y*d.y));
    return Vector3f(d.x, d.y, z);
}

Vector3f rectangle_sample(Vector3f center, Vector3f vx, Vector3f vy) {
    Vector2f u(next_float(), next_float());
    u = 2.f*u - Vector2f(1, 1);

    return center + u.x*vx + u.y*vy;
}