RayDifferential.h

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#pragma once
 
#include "Math/TVector3.h"
 
#include <limits>
 
namespace ph
{
 
class RayDifferential final
{
public:
    RayDifferential();
    RayDifferential(const math::Vector3R& dPdX, const math::Vector3R& dPdY,
                    const math::Vector3R& dDdX, const math::Vector3R& dDdY);
 
    // Propagate differential quantities to some location on a surface the ray
    // has intersected. Specifically, calculate ray differentials on location
    // <surfaceP> with surface normal <surfaceN>.
    void transferToSurface(const math::Vector3R& surfaceP, const math::Vector3R& surfaceN);
 
    // Modify differential quantities as if the ray is reversed in
    // direction.
    inline void reverse()
    {
        m_dDdX.mulLocal(-1);
        m_dDdY.mulLocal(-1);
    }
 
    inline void setPartialPs(const math::Vector3R& dPdX, const math::Vector3R& dPdY)
    {
        m_dPdX = dPdX;
        m_dPdY = dPdY;
 
        m_isPartialPsNonZero = isVectorNonZero(dPdX) || isVectorNonZero(dPdY);
    }
 
    inline void setPartialDs(const math::Vector3R& dDdX, const math::Vector3R& dDdY)
    {
        m_dDdX = dDdX;
        m_dDdY = dDdY;
 
        m_isPartialDsNonZero = isVectorNonZero(dDdX) || isVectorNonZero(dDdY);
    }
 
    inline const math::Vector3R& getdPdX() const { return m_dPdX; }
    inline const math::Vector3R& getdPdY() const { return m_dPdY; }
    inline const math::Vector3R& getdDdX() const { return m_dDdX; }
    inline const math::Vector3R& getdDdY() const { return m_dDdY; }
 
    inline bool isNonZero() const { return m_isPartialPsNonZero || m_isPartialDsNonZero; }
 
private:
    // A point P on a ray.
    math::Vector3R m_P;
 
    // Direction D of a ray.
    math::Vector3R m_D;
 
    // Partial derivatives for P & D with respect to raster coordinates x & y.
    math::Vector3R m_dPdX, m_dPdY;
    math::Vector3R m_dDdX, m_dDdY;
 
    bool m_isPartialPsNonZero;
    bool m_isPartialDsNonZero;
 
    static inline bool isVectorNonZero(const math::Vector3R& vec)
    {
        return vec.lengthSquared() > std::numeric_limits<real>::epsilon();
    }
};
 
}// end namespace ph