Samplers-Impl.hpp

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// This code is based on Jet framework.
// Copyright (c) 2018 Doyub Kim
// CubbyFlow is voxel-based fluid simulation engine for computer games.
// Copyright (c) 2020 CubbyFlow Team
// Core Part: Chris Ohk, Junwoo Hwang, Jihong Sin, Seungwoo Yoo
// AI Part: Dongheon Cho, Minseo Kim
// We are making my contributions/submissions to this project solely in our
// personal capacity and are not conveying any rights to any intellectual
// property of any third parties.

// Copyright (c) 1998-2014, Matt Pharr and Greg Humphreys.
// All rights reserved.

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#ifndef CUBBYFLOW_SAMPLERS_IMPL_HPP
#define CUBBYFLOW_SAMPLERS_IMPL_HPP

namespace CubbyFlow
{
template <typename T>
Vector3<T> UniformSampleCone(T u1, T u2, const Vector3<T>& axis, T angle)
{
    T cosAngle_2 = std::cos(angle / 2);
    T y = 1 - (1 - cosAngle_2) * u1;
    T r = std::sqrt(std::max<T>(0, 1 - y * y));
    T phi = static_cast<T>(2.0 * PI<T>()) * u2;
    T x = r * std::cos(phi);
    T z = r * std::sin(phi);
    auto ts = axis.Tangentials();

    return std::get<0>(ts) * x + axis * y + std::get<1>(ts) * z;
}

template <typename T>
Vector3<T> UniformSampleHemisphere(T u1, T u2, const Vector3<T>& normal)
{
    T y = u1;
    T r = std::sqrt(std::max<T>(0, 1 - y * y));
    T phi = static_cast<T>(2.0 * PI<T>()) * u2;
    T x = r * std::cos(phi);
    T z = r * std::sin(phi);
    auto ts = normal.Tangentials();

    return std::get<0>(ts) * x + normal * y + std::get<1>(ts) * z;
}

template <typename T>
Vector3<T> CosineWeightedSampleHemisphere(T u1, T u2, const Vector3<T>& normal)
{
    T phi = static_cast<T>(2.0 * PI<T>()) * u1;
    T y = std::sqrt(u2);
    T theta = std::acos(y);
    T x = std::cos(phi) * std::sin(theta);
    T z = std::sin(phi) * std::sin(theta);
    Vector3<T> t = Tangential(normal);
    auto ts = normal.Tangentials();

    return std::get<0>(ts) * x + normal * y + std::get<1>(ts) * z;
}

template <typename T>
Vector3<T> UniformSampleSphere(T u1, T u2)
{
    T y = 1 - 2 * u1;
    T r = std::sqrt(std::max<T>(0, 1 - y * y));
    T phi = static_cast<T>(2.0 * PI<T>()) * u2;
    T x = r * std::cos(phi);
    T z = r * std::sin(phi);

    return Vector3<T>(x, y, z);
}

template <typename T>
Vector2<T> UniformSampleDisk(T u1, T u2)
{
    T r = std::sqrt(u1);
    T theta = static_cast<T>(2.0 * PI<T>()) * u2;

    return Vector2<T>(r * std::cos(theta), r * std::sin(theta));
}
}  // namespace CubbyFlow

#endif