Bidirectional path vertex data structure. More...

#include <mitsuba/bidir/vertex.h>

Public Member Functions
Sampling-related functions
void	makeEndpoint (const Scene *scene, Float time, ETransportMode mode)
	Generate a path endpoint that can be used to start a random walk. More...

bool	sampleNext (const Scene scene, Sampler sampler, const PathVertex pred, const PathEdge predEdge, PathEdge succEdge, PathVertex succ, ETransportMode mode, bool russianRoulette=false, Spectrum *throughput=NULL)
	Sample the next vertex in a random walk using the default sampling technique implemented by the current vertex. More...

Spectrum	sampleDirect (const Scene scene, Sampler sampler, PathVertex endpoint, PathEdge edge, PathVertex *sample, ETransportMode mode) const
	Direct sampling: given the current vertex as a reference sample an emitter (or sensor) position that has a nonzero emission (or response) towards it. More...

int	sampleSensor (const Scene scene, Sampler sampler, const Point2i &pixelPosition, PathEdge e0, PathVertex v1, PathEdge e1, PathVertex v2)
	Sample the first vertices on a sensor subpath such that they contribute to a specified pixel in the output image. More...

bool	perturbDirection (const Scene scene, const PathVertex pred, const PathEdge predEdge, PathEdge succEdge, PathVertex *succ, const Vector &d, Float dist, EVertexType desiredType, ETransportMode mode)
	Create a perturbed successor vertex and edge. More...

bool	perturbPosition (const Scene scene, Sampler sampler, Float stddev)
	Generate a path endpoint that can be used to start a random walk. More...

Float	perturbPositionPdf (const PathVertex *target, Float stddev) const
	Generate a path endpoint that can be used to start a random walk. More...

bool	propagatePerturbation (const Scene scene, const PathVertex pred, const PathEdge predEdge, PathEdge succEdge, PathVertex *succ, unsigned int componentType, Float dist, EVertexType desiredType, ETransportMode mode)
	Propagate a perturbation through an ideally specular interaction. More...

Query functions
Spectrum	eval (const Scene scene, const PathVertex pred, const PathVertex *succ, ETransportMode mode, EMeasure measure=EArea) const
	Evaluate the terms of the measurement contribution function that are associated with this vertex. More...

Float	evalPdf (const Scene scene, const PathVertex pred, const PathVertex *succ, ETransportMode mode, EMeasure measure=EArea) const
	Compute the density of a successor node. More...

Float	evalPdfDirect (const Scene scene, const PathVertex sample, ETransportMode mode, EMeasure measure=EArea) const
	Compute the area density of a provided emitter or sensor sample with respect the direct sampling technique implemented in sampleDirect(). More...

const Medium *	getTargetMedium (const PathEdge predEdge, const PathVertex succ) const
	Determine the medium that fills the space between the current vertex and a specified successor. More...

const Medium *	getTargetMedium (const PathEdge *predEdge, const Vector &d) const
	Determine the medium that fills the space in direction `d`. More...

Accessors
EVertexType	getType () const
	Return the type associated with this vertex. More...

Point	getPosition () const
	Return the position associated with this vertex. More...

bool	isOnSurface () const
	Check if the vertex lies on a surface. More...

bool	isNullInteraction () const
	Returns whether or not this vertex describes a "null" scattering interaction. More...

bool	isDiffuseInteraction () const
	Returns whether or not this vertex describes a diffuse surface scattering interaction. More...

bool	isAbsorbing () const
	Returns whether or not this vertex describes a 100% absorbing surface. More...

unsigned int	getComponentType () const
	Return the component type associated with this vertex. More...

Normal	getGeometricNormal () const
	Return the geometric surface normal associated with this vertex. More...

Normal	getShadingNormal () const
	Return the shading surface normal associated with this vertex. More...

Float	getTime () const
	Return the time value associated with this node. More...

bool	isSupernode () const
	Is this vertex a supernode? More...

bool	isSensorSupernode () const
	Is this vertex a sensor super-node? More...

bool	isEmitterSupernode () const
	Is this vertex a emitter super-node? More...

bool	isEmitterSample () const
	Is this vertex an emitter sample? More...

bool	isSensorSample () const
	Is this vertex a lens sample? More...

bool	isSurfaceInteraction () const
	Is this vertex a surface interaction? More...

bool	isMediumInteraction () const
	Is this vertex a medium interaction? More...

EndpointRecord &	getEndpointRecord ()
	Return the endpoint record associated with this node. More...

const EndpointRecord &	getEndpointRecord () const
	Return the endpoint record associated with this node (const) More...

PositionSamplingRecord &	getPositionSamplingRecord ()
	Return the position sampling record associated with this node. More...

const PositionSamplingRecord &	getPositionSamplingRecord () const
	Return the position sampling record associated with this node (const) More...

Intersection &	getIntersection ()
	Return the intersection record associated with this node. More...

const Intersection &	getIntersection () const
	Return the intersection record associated with this node (const) More...

MediumSamplingRecord &	getMediumSamplingRecord ()
	Return the medium sampling record associated with this node. More...

const MediumSamplingRecord &	getMediumSamplingRecord () const
	Return the medium sampling record associated with this node. More...

const Point2 &	getSamplePosition () const
	Return the fractional pixel position associated with a sensor sample. More...

const AbstractEmitter *	getAbstractEmitter () const
	Return the abstract emitter associated with a sensor/emitter sample. More...

bool	isDegenerate () const
	Returns whether or not this vertex is degenerate, i.e. its distribution has measure zero. More...

bool	isConnectable () const
	Returns whether or not this vertex can be deterministically connected to other vertices. More...

bool	updateSamplePosition (const PathVertex *succ)
	Special routine for sensor sample vertices: given a successor `succ`, update the fractional pixel position stored in the vertex. More...

bool	getSamplePosition (const PathVertex *succ, Point2 &result) const
	Special routine for sensor sample vertices: given a successor `succ`, return its associated fractional pixel position. More...

Enumerations and Fields
enum	{ EDataSize }
	Denotes the size of the auxiliary data section associated with each node. More...

enum	EVertexType { EInvalid = 0, ESensorSupernode = 1, EEmitterSupernode = 2, ESensorSample = 4, EEmitterSample = 8, ESurfaceInteraction = 16, EMediumInteraction = 32, ESupernode = ESensorSupernode \| EEmitterSupernode, ENormal }
	What kind of vertex is this (e.g. medium, surface, emitter)? More...

EVertexType	type: 7
	Specifies one of several possible path vertex types. More...

bool	degenerate: 1
	Denotes whether this vertex only supports sampling from degenerate distributions. More...

EMeasure	measure: 8
	Denotes the measure associated with the probability densities stored in pdf. More...

uint16_t	componentType
	When the current vertex supports sampling from several components (this currently only applies to BSDF lobes), this attribute records the type sampled component. More...

Spectrum	weight [ETransportModes]
	Measurement contribution weight. More...

Float	pdf [ETransportModes]
	Area density of the two adjacent vertices. More...

Float	rrWeight
	Termination weight due to russian roulette (used by BDPT) More...

uint8_t	data [EDataSize]
	Auxilary node-depependent data associated with each vertex. More...

Miscellaneous
bool	cast (const Scene *scene, EVertexType desired)
	Cast this vertex into an equivalent from having a different type. More...

bool	verify (const Scene scene, const PathVertex adjL, const PathVertex *adjE, ETransportMode mode, std::ostream &os) const
	Verify the cached values stored in this path vertex for consistency. More...

bool	update (const Scene scene, const PathVertex pred, const PathVertex *succ, ETransportMode mode, EMeasure measure=EArea)
	Given the specified predecessor and successor, update the cached values stored in this vertex. More...

PathVertex *	clone (MemoryPool &pool) const
	Create a deep copy of this vertex. More...

std::string	toString () const
	Return a string representation of the information stored in this vertex. More...

bool	operator== (const PathVertex &vertex) const
	Compare this vertex against another vertex. More...

bool	operator!= (const PathVertex &vertex) const
	Compare this vertex against another vertex. More...

static bool	connect (const Scene scene, const PathVertex pred, const PathEdge predEdge, PathVertex vs, PathEdge edge, PathVertex vt, const PathEdge succEdge, const PathVertex succ)
	Create a connection between two disconnected subpaths. More...

static bool	connect (const Scene scene, const PathVertex pred, const PathEdge predEdge, PathVertex vs, PathEdge edge, PathVertex vt, const PathEdge succEdge, const PathVertex succ, EMeasure vsMeasure, EMeasure vtMeasure)
	Like the above, but can be used to connect delta endpoints. More...

Detailed Description

Bidirectional path vertex data structure.

The path vertex data structure represents a basic interaction within the path-space light transport framework. It abstracts away the specifics of the underlying interaction, which simplifies the implementation of bidirectional rendering techniques such as Bidirectional Path Tracing or Veach-style Metropolis Light Transport.

This data structure can describe a several different types of interactions, including surface and medium scattering events, as well as emission events by a light source or a sensor (in the bidirectional framework, the response of a sensor is treated as an emitted quantity)

A path vertex only describes what happens at the location of a scattering or emission event – what happens in between such interactions is captured in a separate data structure named PathEdge.

Author: Wenzel Jakob

Member Enumeration Documentation

anonymous enum

Denotes the size of the auxiliary data section associated with each node.

Enumerator
EDataSize

enum mitsuba::PathVertex::EVertexType

What kind of vertex is this (e.g. medium, surface, emitter)?

The two special 'supernode' types are used as path endpoints, which greatly simplifies the control flow of various functions in this data structure and the MLT/BDPT implementations.

Enumerator
EInvalid	Invalid/uninitialized vertex.
ESensorSupernode	Special sensor 'supernode' – just before the sensor sample.
EEmitterSupernode	Special emitter 'supernode' – just before the emitter sample.
ESensorSample	Sampled position on the surface of a sensor.
EEmitterSample	Sampled position on the surface of an emitter.
ESurfaceInteraction	Interaction with a scene surface.
EMediumInteraction	Interaction with a participating medium.
ESupernode	Union of the two supernode types.
ENormal	Union of all other vertex types.

Member Function Documentation

bool mitsuba::PathVertex::cast	(	const Scene *	scene,
		EVertexType	desired
	)

Cast this vertex into an equivalent from having a different type.

Sometimes it is necessary to cast a vertex into a different type. An example when this occurs is when a surface interaction vertex lies on the surface of an emitter or a sensor. In such a situation, it may be useful to retroactively turn it into an emitter or sensor sample vertex located at the same position. This function allows to do precisely that.

Parameters

scene	A pointer to the underlying scene
desired	Desired type after the cast

Returns: true on success. When returning false, the function did not make any changes.

PathVertex* mitsuba::PathVertex::clone ( MemoryPool & pool ) const

Create a deep copy of this vertex.

static bool mitsuba::PathVertex::connect	(	const Scene *	scene,
		const PathVertex *	pred,
		const PathEdge *	predEdge,
		PathVertex *	vs,
		PathEdge *	edge,
		PathVertex *	vt,
		const PathEdge *	succEdge,
		const PathVertex *	succ
	)

static

Create a connection between two disconnected subpaths.

This function can be used to connect two seperately created emitter and sensor subpaths so that they can be merged into a Path data structure. The function checks that the vertices vs and vt are mutually visible, and that there is a nonzero throughput between them. If that is the case, it updates the cached values stored in vs, edge, and vt.

The expected order of the parameters in path-space is

(pred) -> predEdge -> (vs) -> edge -> (vt) -> succEdge -> (succ)

where entries in parentheses denote vertices, pred is the closer to the light source, and succ is the closer to the sensor.

Parameters

scene	Pointer to the underlying scene
pred	Pointer to the predecessor vertex of `vs` (towards the emitter)
predEdge	Pointer to an edge between `pred` and `vs`.
vs	Last vertex of the emitter subpath to be connected. The cached values of this vertex will be updated should the connection attempt succeed.
edge	Pointer to an unused edge data structure, which will be annotated with information about the medium-related transport between `vs` and `vt`.
vt	Last vertex of the sensor subpath to be connected. The cached values of this vertex will be updated should the connection attempt succeed.
succEdge	Pointer to an edge between `vt` and `succ`.
succ	Pointer to the successor vertex of `vt` (towards the sensor)

Returns: true upon success, false when there is no throughput or an inconsistency has been detected.

static bool mitsuba::PathVertex::connect	(	const Scene *	scene,
		const PathVertex *	pred,
		const PathEdge *	predEdge,
		PathVertex *	vs,
		PathEdge *	edge,
		PathVertex *	vt,
		const PathEdge *	succEdge,
		const PathVertex *	succ,
		EMeasure	vsMeasure,
		EMeasure	vtMeasure
	)

static

Like the above, but can be used to connect delta endpoints.

Spectrum mitsuba::PathVertex::eval	(	const Scene *	scene,
		const PathVertex *	pred,
		const PathVertex *	succ,
		ETransportMode	mode,
		EMeasure	measure = `EArea`
	)		const

Evaluate the terms of the measurement contribution function that are associated with this vertex.

Compute a single term of the contribution weighting function associated with the current node given a predecessor and successor node.

Note: this function only accounts for the factor associated with this specific vertex – to account for an adjacent edge, refer to PathEdge::eval.

Parameters

scene	Pointer to the underlying scene
pred	Pointer to the preceding vertex (if any) and `NULL` otherwise
succ	Pointer to the successor vertex (if any) and `NULL` otherwise
mode	Specifies whether radiance or importance is being transported
measure	Specifies the measure of the queried component. This is necessary to handle mixture scattering functions, whose components are defined on spaces with different measures.

Returns: The contribution weighting factor

Float mitsuba::PathVertex::evalPdf	(	const Scene *	scene,
		const PathVertex *	pred,
		const PathVertex *	succ,
		ETransportMode	mode,
		EMeasure	measure = `EArea`
	)		const

Compute the density of a successor node.

This function computes the hypothetical scattering-related sampling density of a given successor node when using the sampling technique implemented by sampleNext(). Since this technique conditions on a predecessor vertex, it must also be provided here. The desired measure (e.g. area/solid angle/discrete) can be provided as an extra parameter.

Note: this function only computes probability associated with the vertices – to account for edges, refer to PathEdge::evalPdf.

Parameters

scene	Pointer to the underlying scene
pred	Pointer to the preceding vertex (if any) and `NULL` otherwise
succ	Pointer to the successor vertex (if any) and `NULL` otherwise
mode	Specifies whether radiance or importance is being transported
measure	Specifies the measure of the queried component. This is necessary to handle mixture scattering functions, whose components are defined on spaces with different measures.

Returns: The computed probability density

Float mitsuba::PathVertex::evalPdfDirect	(	const Scene *	scene,
		const PathVertex *	sample,
		ETransportMode	mode,
		EMeasure	measure = `EArea`
	)		const

Compute the area density of a provided emitter or sensor sample with respect the direct sampling technique implemented in sampleDirect().

The current vertex is taken to be the reference point of the direct sampling technique.

Parameters

scene	Pointer to the underlying scene
mode	Specifies whether radiance or importance is being transported
sample	An emitter or sensor sample
measure	Specifies the measure of the queried component. This is necessary to handle scattering functions, whose components are defined on spaces with different measures.

Returns: The density of sample conditioned on this vertex.

const AbstractEmitter* mitsuba::PathVertex::getAbstractEmitter ( ) const

inline

Return the abstract emitter associated with a sensor/emitter sample.

unsigned int mitsuba::PathVertex::getComponentType ( ) const

inline

Return the component type associated with this vertex.

This currently only applies to surface interactions. The returned result will consist of flags in BSDF::EBSDFType.

EndpointRecord& mitsuba::PathVertex::getEndpointRecord ( )

inline

Return the endpoint record associated with this node.

const EndpointRecord& mitsuba::PathVertex::getEndpointRecord ( ) const

inline

Return the endpoint record associated with this node (const)

Normal mitsuba::PathVertex::getGeometricNormal ( ) const

Return the geometric surface normal associated with this vertex.

Throws an exception when called on a supernode or a medium interaction

Intersection& mitsuba::PathVertex::getIntersection ( )

inline

Return the intersection record associated with this node.

const Intersection& mitsuba::PathVertex::getIntersection ( ) const

inline

Return the intersection record associated with this node (const)

MediumSamplingRecord& mitsuba::PathVertex::getMediumSamplingRecord ( )

inline

Return the medium sampling record associated with this node.

const MediumSamplingRecord& mitsuba::PathVertex::getMediumSamplingRecord ( ) const

inline

Return the medium sampling record associated with this node.

Point mitsuba::PathVertex::getPosition ( ) const

Return the position associated with this vertex.

Throws an exception when called on a supernode

PositionSamplingRecord& mitsuba::PathVertex::getPositionSamplingRecord ( )

inline

Return the position sampling record associated with this node.

const PositionSamplingRecord& mitsuba::PathVertex::getPositionSamplingRecord ( ) const

inline

Return the position sampling record associated with this node (const)

const Point2& mitsuba::PathVertex::getSamplePosition ( ) const

inline

Return the fractional pixel position associated with a sensor sample.

bool mitsuba::PathVertex::getSamplePosition	(	const PathVertex *	succ,
		Point2 &	result
	)		const

Special routine for sensor sample vertices: given a successor succ, return its associated fractional pixel position.

Parameters

v	Pointer to the target vertex
result	Reference to a 2D point that will be set to the fractional pixel coordinates associated with `succ`.

Returns: true upon success (i.e. when the point is in the sensor's field of view)

Normal mitsuba::PathVertex::getShadingNormal ( ) const

Return the shading surface normal associated with this vertex.

Throws an exception when called on a supernode or a medium interaction

const Medium* mitsuba::PathVertex::getTargetMedium	(	const PathEdge *	predEdge,
		const PathVertex *	succ
	)		const

Determine the medium that fills the space between the current vertex and a specified successor.

This function assumes that there is no surface between this and succ, hence it does not account for intermediate medium changes.

Parameters

predEdge	Pointer to an edge that connects the current node to its predecessor
succ	Pointer to the successor vertex in question

Returns: The medium between this and succ

const Medium* mitsuba::PathVertex::getTargetMedium	(	const PathEdge *	predEdge,
		const Vector &	d
	)		const

Determine the medium that fills the space in direction d.

Parameters

predEdge	Pointer to an edge that connects the current node to its predecessor
d	A world-space direction

Returns: The medium containing the ray (this->getPosition(), d)

Float mitsuba::PathVertex::getTime ( ) const

Return the time value associated with this node.

EVertexType mitsuba::PathVertex::getType ( ) const

inline

Return the type associated with this vertex.

bool mitsuba::PathVertex::isAbsorbing ( ) const

inline

Returns whether or not this vertex describes a 100% absorbing surface.

Such is the case on emitters/sensors that don't have an explicit BSDF assigned to them. It is useful to be able to query this to avoid some useless connection attempts involving these vertices.

bool mitsuba::PathVertex::isConnectable ( ) const

inline

Returns whether or not this vertex can be deterministically connected to other vertices.

This is the case when degenerate == false and measure != EDiscrete.

bool mitsuba::PathVertex::isDegenerate ( ) const

inline

Returns whether or not this vertex is degenerate, i.e. its distribution has measure zero.

bool mitsuba::PathVertex::isDiffuseInteraction ( ) const

inline

Returns whether or not this vertex describes a diffuse surface scattering interaction.

bool mitsuba::PathVertex::isEmitterSample ( ) const

inline

Is this vertex an emitter sample?

bool mitsuba::PathVertex::isEmitterSupernode ( ) const

inline

Is this vertex a emitter super-node?

bool mitsuba::PathVertex::isMediumInteraction ( ) const

inline

Is this vertex a medium interaction?

bool mitsuba::PathVertex::isNullInteraction ( ) const

inline

Returns whether or not this vertex describes a "null" scattering interaction.

A null interaction is a degenerate scattering event with a Dirac delta peak in the forward direction. Apart from a potential influence on their weight, particles will pass through such an interface unchanged.

bool mitsuba::PathVertex::isOnSurface ( ) const

inline

Check if the vertex lies on a surface.

bool mitsuba::PathVertex::isSensorSample ( ) const

inline

Is this vertex a lens sample?

bool mitsuba::PathVertex::isSensorSupernode ( ) const

inline

Is this vertex a sensor super-node?

bool mitsuba::PathVertex::isSupernode ( ) const

inline

Is this vertex a supernode?

bool mitsuba::PathVertex::isSurfaceInteraction ( ) const

inline

Is this vertex a surface interaction?

void mitsuba::PathVertex::makeEndpoint	(	const Scene *	scene,
		Float	time,
		ETransportMode	mode
	)

Generate a path endpoint that can be used to start a random walk.

Parameters

scene	Pointer to the underlying scene
mode	Specifies the desired mode of transport, i.e. radiance or importance transport
time	Denotes the time value that will be associated with this endpoint and any paths generated starting from there.

bool mitsuba::PathVertex::operator!= ( const PathVertex & vertex ) const

inline

Compare this vertex against another vertex.

bool mitsuba::PathVertex::operator== ( const PathVertex & vertex ) const

Compare this vertex against another vertex.

bool mitsuba::PathVertex::perturbDirection	(	const Scene *	scene,
		const PathVertex *	pred,
		const PathEdge *	predEdge,
		PathEdge *	succEdge,
		PathVertex *	succ,
		const Vector &	d,
		Float	dist,
		EVertexType	desiredType,
		ETransportMode	mode
	)

Create a perturbed successor vertex and edge.

This function behaves similar to sampleNext() in that it generates a successor edge and vertex.

The main difference is that the desired direction, distance, and type of the successor vertex are all specified, which makes the sampling process completely deterministic. This is useful for implementing path-space perturbation strategies.

This function only applies to non-supernode vertices.

Parameters

scene	Pointer to the underlying scene
pred	Pointer to the preceding vertex (if any) and `NULL` otherwise
predEdge	Edge to the preceding edge (if any) and `NULL` otherwise
succEdge	Pointer to an unused edge data structure, which will be filled with information about the edge between the current vertex and the new successor.
succ	Pointer to an unused vertex data structure, which will be filled with information about the successor vertex
d	Specifies the desired outgoing direction at the current vertex
dist	Specifies the desired distance between the current vertex and `succ` (this only applies when `desiredType=EMediumInteraction`)
desiredType	Specifies the desired vertex type of `succ`.
mode	Specifies whether radiance or importance is being transported

Returns: true on success

bool mitsuba::PathVertex::perturbPosition	(	const Scene *	scene,
		Sampler *	sampler,
		Float	stddev
	)

Generate a path endpoint that can be used to start a random walk.

Parameters

scene	Pointer to the underlying scene
mode	Specifies the desired mode of transport, i.e. radiance or importance transport
time	Denotes the time value that will be associated with this endpoint and any paths generated starting from there.

Float mitsuba::PathVertex::perturbPositionPdf	(	const PathVertex *	target,
		Float	stddev
	)		const

Generate a path endpoint that can be used to start a random walk.

Parameters

scene	Pointer to the underlying scene
mode	Specifies the desired mode of transport, i.e. radiance or importance transport
time	Denotes the time value that will be associated with this endpoint and any paths generated starting from there.

bool mitsuba::PathVertex::propagatePerturbation	(	const Scene *	scene,
		const PathVertex *	pred,
		const PathEdge *	predEdge,
		PathEdge *	succEdge,
		PathVertex *	succ,
		unsigned int	componentType,
		Float	dist,
		EVertexType	desiredType,
		ETransportMode	mode
	)

Propagate a perturbation through an ideally specular interaction.

This function behaves similar to sampleNext() and perturbDirection() in that it generates a successor edge and vertex.

The main difference is that it only works for specular interactions, where the requested type of interaction (reflection/refraction) is additionally specified, which makese the sampling process completely deterministic. This is useful for implementing path-space perturbation strategies. For now, it is only used by the perturbations of Veach and Guibas.

This function only applies to surface interaction vertices.

Parameters

scene	Pointer to the underlying scene
pred	Pointer to the preceding vertex (if any) and `NULL` otherwise
predEdge	Edge to the preceding edge (if any) and `NULL` otherwise
succEdge	Pointer to an unused edge data structure, which will be filled with information about the edge between the current vertex and the new successor.
dist	Specifies the desired distance between the current vertex and `succ` (this only applies when `desiredType=EMediumInteraction`)
desiredType	Specifies the desired vertex type of `succ`.
componentType	Specifies the desired type of scattering interaction (equivalent to BSDF::typeMask)
succ	Pointer to an unused vertex data structure, which will be filled with information about the successor vertex
dist	Specifies the desired distance between the current vertex and `succ` (this only applies to medium interactions)
mode	Specifies whether radiance or importance is being transported

Returns: true on success

Spectrum mitsuba::PathVertex::sampleDirect	(	const Scene *	scene,
		Sampler *	sampler,
		PathVertex *	endpoint,
		PathEdge *	edge,
		PathVertex *	sample,
		ETransportMode	mode
	)		const

Direct sampling: given the current vertex as a reference sample an emitter (or sensor) position that has a nonzero emission (or response) towards it.

This can be seen as a generalization of direct illumination sampling that can be used for both emitter and sensor endpoints.

Ideally, the implementation should importance sample the product of the emission or response profile and the geometry term between the reference point and the sampled position. In practice, one of these usually has to be sacrificed.

Parameters

scene	Pointer to the underlying scene
sampler	Pointer to a sample generator
endpoint	Unused vertex data structure, which will be configured as the endpoint associated with `sample`.
edge	Unused edge data structure, which will be configured as the edge between `endpoint` and `sample`.
sample	Unused vertex data structure, which will hold the sampled sensor or emitter position
mode	Specifies whether radiance or importance is being transported

Returns: The emitted radiance or importance divided by the sample probability per unit area per unit solid angle.

bool mitsuba::PathVertex::sampleNext	(	const Scene *	scene,
		Sampler *	sampler,
		const PathVertex *	pred,
		const PathEdge *	predEdge,
		PathEdge *	succEdge,
		PathVertex *	succ,
		ETransportMode	mode,
		bool	russianRoulette = `false`,
		Spectrum *	throughput = `NULL`
	)

Sample the next vertex in a random walk using the default sampling technique implemented by the current vertex.

Given a vertex, its predecessor, as well as the edge in between them, this function samples a new successor edge and vertex.

Parameters

scene	Pointer to the underlying scene
sampler	Pointer to a sample generator
pred	Pointer to the preceding vertex (if any) and `NULL` otherwise
predEdge	Edge to the preceding edge (if any) and `NULL` otherwise
succEdge	Pointer to an unused edge data structure, which will be filled with information about the edge between the current vertex and the newly sampled successor.
succ	Pointer to an unused vertex data structure, which will be filled with information about the successor vertex
mode	Specifies whether radiance or importance is being transported
russianRoulette	Should russian roulette be used while sampling the successor? Note that the effects of this are only captured in the `rrWeight` field – the weight and pdf fields intentionally remain unchanged.
throughput	If russian roulette is active, this parameter should point to a spectrum value that is used to record the aggregate path weight thus far. It will be updated automatically to account for the current interaction.

Returns: true on success

int mitsuba::PathVertex::sampleSensor	(	const Scene *	scene,
		Sampler *	sampler,
		const Point2i &	pixelPosition,
		PathEdge *	e0,
		PathVertex *	v1,
		PathEdge *	e1,
		PathVertex *	v2
	)

Sample the first vertices on a sensor subpath such that they contribute to a specified pixel in the output image.

This function samples the spatial and directional components of the sensor and is similar to calling sampleNext() two times in sequence starting from a sensor supernode. The main difference is that the resulting subpath passes through a specified pixel position, which is important to implement algorithms that parallelize rendering of images by processing it in separate blocks. If this function is called once for every pixel in the output image, the resulting path distribution is identical to what would have been obtained via sampleNext().

The function throws an exception when the current vertex is not a sensor supernode.

Parameters

scene	Pointer to the underlying scene
sampler	Pointer to a sample generator
pixelPosition	Specifies the desired pixel position
e0	Pointer to the first edge on the sensor subpath
e0	Pointer to the first edge on the sensor subpath
v1	Pointer to the second vertex on the sensor subpath
v2	Pointer to the third vertex on the sensor subpath

Returns: The number of successful sampling operations (i.e. 0 if sensor sampling failed, 1 if no surface/medium interaction was encountered, or 2 if all data structures were successfully filled)

std::string mitsuba::PathVertex::toString ( ) const

Return a string representation of the information stored in this vertex.

bool mitsuba::PathVertex::update	(	const Scene *	scene,
		const PathVertex *	pred,
		const PathVertex *	succ,
		ETransportMode	mode,
		EMeasure	measure = `EArea`
	)

Given the specified predecessor and successor, update the cached values stored in this vertex.

Parameters

pred	Pointer to the predecessor vertex (if any) and `NULL` otherwise
succ	Pointer to the successor vertex (if any) and `NULL` otherwise
mode	Specifies the direction of light transport

Returns: false when there is no throughput

bool mitsuba::PathVertex::updateSamplePosition ( const PathVertex * succ )

Special routine for sensor sample vertices: given a successor succ, update the fractional pixel position stored in the vertex.

Parameters

v	Pointer to the target vertex

Returns: true upon success (i.e. when the point is in the sensor's field of view)

bool mitsuba::PathVertex::verify	(	const Scene *	scene,
		const PathVertex *	adjL,
		const PathVertex *	adjE,
		ETransportMode	mode,
		std::ostream &	os
	)		const

Verify the cached values stored in this path vertex for consistency.

This function re-evaluates a series of quantities associated with this vertex and compares them to locally cached values including pdf, value, and degenerate. If any mismatch is found, the function sends debug output to a specified output stream and returns false.

Parameters

scene	Pointer to the underlying scene
pred	Pointer to the preceding vertex (if any) and `NULL` otherwise
succ	Pointer to the successor vertex (if any) and `NULL` otherwise
mode	Transport mode – disambiguates the meaning of `pred` and `succ`.
os	Target output stream for error messages

Member Data Documentation

uint16_t mitsuba::PathVertex::componentType

When the current vertex supports sampling from several components (this currently only applies to BSDF lobes), this attribute records the type sampled component.

Otherwise, it will be set to zero.

uint8_t mitsuba::PathVertex::data[EDataSize]

Auxilary node-depependent data associated with each vertex.

This "payload" field is large enough to describe any possible kind of vertex. Currently, it is cast to the desired type of data structure which wreaks havoc with strict aliasing (and hence it is disabled for all bidirectional code).

Once C++11 is widely supported across all target platforms, this should be replaced by an unrestricted union.

bool mitsuba::PathVertex::degenerate

Denotes whether this vertex only supports sampling from degenerate distributions.

It's useful to cache this information, since it allows to quickly determine when certain pairs of vertices cannot be deterministically connected.

Examples of degenerate vertices are surface interactions with dielectric boundaries and certain special cases. For instance, the sensor supernode can be degenerate when the used sensor does not cover any area (e.g. because it is a point camera).

EMeasure mitsuba::PathVertex::measure

Denotes the measure associated with the probability densities stored in pdf.

Certain vertices use sampling methods, whose probability mass lies on domains that have different associated measures. An example would be a surface interaction with a smooth plastic material, where the specular reflection component is degenerate and the glossy reflection component is non-degenerate.

This attribute stores the actual measure (an enumeration item of type EMeasure) and therefore clarifies whether or not a degenerate component was sampled. When no sampling event was generated yet, it is undefined.

Currently, only three values are permissible: EArea, EDiscrete, or EInvalidMeasure.

See Also: EMeasure

Float mitsuba::PathVertex::pdf[ETransportModes]

Area density of the two adjacent vertices.

This field stores the density of the predecessor and sucessor nodes with respect of the sampling technique implemented by sampleNext(). The measure of this value is specified by the measure field (generally, it is the density per unit area).

When one of the adjacent vertices is a medium interaction (i.e. it is not located on a surface), the stored probability will specify the density on a hypothetical surface oriented perpendicularly to the transport direction.

Note that this field does not account for medium-related terms. When an adjacent vertex is a medium interaction, its volume density can be recovered by computing the product of pdf and PathEdge::pdf of the associated transport edge.

Float mitsuba::PathVertex::rrWeight

Termination weight due to russian roulette (used by BDPT)

EVertexType mitsuba::PathVertex::type

Specifies one of several possible path vertex types.

See Also: EVertexType

Spectrum mitsuba::PathVertex::weight[ETransportModes]

Measurement contribution weight.

This field stores the terms of the path-space measurement contribution function that are coupled to this specific vertex, divided by the density of the adjacent vertices in the radiance and importance transport directions (hence, it is an array with two entries).

More precisely, it stores

\[ f(\mathbf{x}_{i-1}\to \mathbf{x}_i\to\mathbf{x}_{i+1})\, G(\mathbf{x}_i\leftrightarrow\mathbf{x}_{i+1})\,p_A(\mathbf{x}_{i-1}\to \mathbf{x}_i\to\mathbf{x}_{i+1})^{-1} \]

and

\[ f(\mathbf{x}_{i+1}\to \mathbf{x}_i\to\mathbf{x}_{i-1})\, G(\mathbf{x}_i\leftrightarrow\mathbf{x}_{i-1})\,p_A(\mathbf{x}_{i+1}\to \mathbf{x}_i\to\mathbf{x}_{i-1})^{-1} \]

Where \(G\) is the geometric term, \(p_A\) is an area density, and increasing indices are closer to the sensor. Generally much cancellation will occur in the above expressions. For instance, for a surface iteractions, this is equal to the BRDF times a cosine foreshortening factor divided by the solid angle density of the default sampling method.

Note that this field does not account for medium-related terms. These can be found in PathEdge::weight

The documentation for this struct was generated from the following file:

include/mitsuba/bidir/vertex.h

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