PreethamTexture.h

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#pragma once
 
#include "Core/Texture/TTexture.h"
#include "Math/Color/Spectrum.h"
#include "Math/TVector3.h"
 
#include <Common/primitive_type.h>
 
#include <memory>
#include <cmath>
 
namespace ph
{
 
class PreethamTexture : public TTexture<math::Spectrum>
{
public:
    PreethamTexture(
        real phiSun,
        real thetaSun,
        real turbidity,
        real energyScale = 1.0_r);
 
    void sample(const SampleLocation& sampleLocation, math::Spectrum* out_value) const override;
 
private:
    real           m_phiSun;
    real           m_thetaSun;
    math::Vector3R m_A_xyY;
    math::Vector3R m_B_xyY;
    math::Vector3R m_C_xyY;
    math::Vector3R m_D_xyY;
    math::Vector3R m_E_xyY;
    math::Vector3R m_Yabs_xyY;
    real           m_energyScale;
 
    math::Vector3R F(real theta, real cosGamma) const;
};
 
// In-header Implementations:
 
inline math::Vector3R PreethamTexture::F(const real theta, const real cosGamma) const
{
    const auto rcpCosTheta = 1.0_r / std::cos(theta);
 
    // Gamma is the angle between direction to sun and view vector
    const auto gamma     = std::acos(cosGamma);
    const auto cos2Gamma = cosGamma * cosGamma;
 
    return {
        (1.0_r + m_A_xyY.x() * std::exp(m_B_xyY.x() * rcpCosTheta)) * (1.0_r + m_C_xyY.x() * std::exp(m_D_xyY.x() * gamma) + m_E_xyY.x() * cos2Gamma),
        (1.0_r + m_A_xyY.y() * std::exp(m_B_xyY.y() * rcpCosTheta)) * (1.0_r + m_C_xyY.y() * std::exp(m_D_xyY.y() * gamma) + m_E_xyY.y() * cos2Gamma),
        (1.0_r + m_A_xyY.z() * std::exp(m_B_xyY.z() * rcpCosTheta)) * (1.0_r + m_C_xyY.z() * std::exp(m_D_xyY.z() * gamma) + m_E_xyY.z() * cos2Gamma)};
}
 
}// end namespace ph