Samplers-Impl.h

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/*************************************************************************
> File Name: Samplers-Impl.h
> Project Name: CubbyFlow
> Author: Chan-Ho Chris Ohk
> Purpose: Sampler functions for CubbyFlow.
> Created Time: 2017/06/21
> Copyright (c) 2018, Chan-Ho Chris Ohk
*************************************************************************/

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

// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:

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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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#ifndef CUBBYFLOW_SAMPLERS_IMPL_H
#define CUBBYFLOW_SAMPLERS_IMPL_H

namespace CubbyFlow
{
    template <typename T>
    inline 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.Tangential();

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

    template <typename T>
    inline 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.Tangential();

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

    template <typename T>
    inline 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.Tangential();

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

    template <typename T>
    inline 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>
    inline 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));
    }
}

#endif