ph::lta Namespace Reference

Light transport algorithms. More...

Classes
class	PDF
	A sample from a Probability Density Function (PDF). More...
class	PtVolumetricEstimator
class	RussianRoulette
	Russian roulette random termination scheme. More...
class	SenseEvent
class	SidednessAgreement
class	SurfaceHitRefinery
	Algorithms for various hit point adjustments. For surface escaping routines, the generated ray is not guaranteed to "actually" avoid the surface. In other words, self-intersection may still happen under different circumstances dpending on the method used. More...
class	SurfaceTracer
	Common operations for surface tracing. This class also handles many subtle cases for surface tracing. You may take the implementations here as reference if a more fine-grained control is needed for a custom operation. More...
class	TDirectLightEstimator
	Estimate direct lighting for a surface point. This is a lightweight helper type for estimating direct lighting. Do not think "direct light" as lighting from a directional light source, it means the first-bounce lighting for any surface point, and the surface point can be the N-th one in a path. More...
class	TIndirectLightEstimator
	Estimate indirect lighting for a surface point. More...
class	TMIS
	Static helper for Multiple Importance Sampling (MIS). See the paper by Veach et al. [17] for more theoretical background. More...

Enumerations
enum class	EMISStyle : uint8 { Balance , Power }
	Type of Multiple Importance Sampling (MIS). More...
enum class	EDomain : uint8 {   Empty = 0 , SolidAngle , HalfSolidAngle , Area ,   UV01 , UVW01 , Discrete }
	Type of the set of all possible inputs for a mathematical function. More...
enum class	ETransport { Radiance , Importance }
	Type of the transported quantity. More...
enum class	ESidednessPolicy { DoNotCare , Strict , TrustGeometry , TrustShading }

Functions
real	pdfA_to_pdfW (const real pdfA, const math::Vector3R &dAPosToTargetPos, const math::Vector3R &dANormal)
	Transform area domain PDF to solid angle domain PDF w.r.t. a position.
real	importance_scatter_Ns_corrector (const math::Vector3R &Ns, const math::Vector3R &Ng, const math::Vector3R &L, const math::Vector3R &V)
real	importance_BSDF_Ns_corrector (const math::Vector3R &Ns, const math::Vector3R &Ng, const math::Vector3R &V)
real	tamed_importance_scatter_Ns_corrector (const math::Vector3R &Ns, const math::Vector3R &Ng, const math::Vector3R &L, const math::Vector3R &V)
	Smoother version of importance_scatter_Ns_corrector().
real	tamed_importance_BSDF_Ns_corrector (const math::Vector3R &Ns, const math::Vector3R &Ng, const math::Vector3R &V)
	Smoother version of importance_BSDF_Ns_corrector(). See tamed_importance_scatter_Ns_corrector() for explanation.

Detailed Description

Light transport algorithms.

Enumeration Type Documentation

EDomain

enum class ph::lta::EDomain : uint8

strong

Type of the set of all possible inputs for a mathematical function.

Enumerator
Empty
SolidAngle
HalfSolidAngle
Area
UV01
UVW01
Discrete

EMISStyle

enum class ph::lta::EMISStyle : uint8

strong

Type of Multiple Importance Sampling (MIS).

Enumerator
Balance
Power

ESidednessPolicy

enum class ph::lta::ESidednessPolicy

strong

Options for dealing with situations where a vector is within the hemisphere defined by geometry normal but outside the one defined by shading normal or vice versa.

Enumerator
DoNotCare	Perform any calculations without caring sidedness agreement.
Strict	A vector must lies in hemispheres defined by geometry normal and shading normal simultaneously.
TrustGeometry	Judging sidedness agreement solely on geometry normal.
TrustShading	Judging sidedness agreement solely on shading normal.

ETransport

enum class ph::lta::ETransport

strong

Type of the transported quantity.

Enumerator
Radiance
Importance

Function Documentation

importance_BSDF_Ns_corrector()

real ph::lta::importance_BSDF_Ns_corrector ( const math::Vector3R & Ns, const math::Vector3R & Ng, const math::Vector3R & V )

inline

This correction factor is for the same reason as importance_scatter_Ns_corrector(), to restore the consistency of importance transport when shading normal is used for light transport. This factor works on the BSDF itself only. Using this factor accounts the fact that shading normals make a BSDF asymmetric during light/importance transport.

This factor does not take the geometry factor Ns.dot(L) into account. It considers the BSDF only.

Parameters

Ns	Shading normal.
Ng	Geometry normal.
V	Direction of excitant importance.

Note

All vectors are expected to be in unit length and leaving the surface.

importance_scatter_Ns_corrector()

real ph::lta::importance_scatter_Ns_corrector ( const math::Vector3R & Ns, const math::Vector3R & Ng, const math::Vector3R & L, const math::Vector3R & V )

inline

Using shading normal for light transport algorithms is equivalent to using asymmetric BSDFs. This can lead to inconsistent results between regular and adjoint algorithms. This correction factor, when multiplied with the weight of an importance scatter event, restores the consistency when adjoint algorithms also use shading normals during importance transport.

This factor also considers the geometry factor Ns.dot(L). The geometry factor is expected to be used (multiplied) together with this factor.

References: [1] Eric Veach, "Non-symmetric Scattering in Light Transport Algorithms", Eurographics Rendering Workshop 1996 Proceedings.

Parameters

Ns	Shading normal.
Ng	Geometry normal.
L	Direction of incident importance.
V	Direction of excitant importance.

Note

All vectors are expected to be in unit length and leaving the surface.

pdfA_to_pdfW()

real ph::lta::pdfA_to_pdfW ( const real pdfA, const math::Vector3R & dAPosToTargetPos, const math::Vector3R & dANormal )

inline

Transform area domain PDF to solid angle domain PDF w.r.t. a position.

tamed_importance_BSDF_Ns_corrector()

real ph::lta::tamed_importance_BSDF_Ns_corrector ( const math::Vector3R & Ns, const math::Vector3R & Ng, const math::Vector3R & V )

inline

Smoother version of importance_BSDF_Ns_corrector(). See tamed_importance_scatter_Ns_corrector() for explanation.

tamed_importance_scatter_Ns_corrector()

real ph::lta::tamed_importance_scatter_Ns_corrector ( const math::Vector3R & Ns, const math::Vector3R & Ng, const math::Vector3R & L, const math::Vector3R & V )

inline

Smoother version of importance_scatter_Ns_corrector().

The weighting for importance transport is only correct (same scene interpretation and rendered result) if we account for the BSDF asymmetry when shading normal is used. However, this factor introduces high variance (big firefly marks). This version attempts to lower the variance by removing large correction factor (and this introduces bias, though not easily noticeable).

In PBRT-v3, this factor is completely ignored. In Mitsuba 0.6, this factor is only applied on last bounce, i.e., during radiance estimation (applying the importance_BSDF_Ns_corrector(), not the scattering/throughput one).