The RixBxdf interface is a shading plugin responsible for creating a RixBxdf from the the ShadingContext and the set of connected patterns. More...

#include <RixBxdf.h>

Inherited by RixNullBxdf.

Public Types
enum	BxdfProperty { k_Albedo, k_MaterialIor }

Public Member Functions
	RixBxdf (RixShadingContext const sCtx, RixBxdfFactory factory)

virtual	~RixBxdf ()

RixShadingContext const *	GetShadingCtx ()

RixBxdfFactory *	GetBxdfFactory ()

virtual RixBXEvaluateDomain	GetEvaluateDomain ()=0
	The domain over which this Bxdf evaluates samples. More...

virtual void	GetAggregateLobeTraits (RixBXLobeTraits *t)=0
	The types of samples this BxdfEvaluator can generate. More...

PRMAN_INLINE RixBXLobeTraits	GetAllLobeTraits ()

virtual RixSCDetail	GetProperty (BxdfProperty property, void const **result) const =0
	Get material property Bxdfs can be queried for general material properties to facilitate integration tasks. More...

virtual bool	EmitLocal (RtColorRGB *result)=0
	Used for baked, pre-integrated, indirect results. More...

virtual void	GenerateSample (RixBXTransportTrait transportTrait, RixBXLobeTraits const lobesWanted, RixRNG rng, RixBXLobeSampled lobesSampled, RtVector3 directions, RixBXLobeWeights &weights, float forwardPdfs, float reversePdfs, RtColorRGB *compTrans=NULL)=0
	Generate sample data for each point. More...

virtual void	EvaluateSample (RixBXTransportTrait transportTrait, RixBXLobeTraits const lobesWanted, RixRNG rng, RixBXLobeTraits lobesEvaluated, RtVector3 const directions, RixBXLobeWeights &weights, float forwardPdfs, float reversePdfs)=0
	Bxdf is expected to evaluate itself subject to the lobesWanted request. More...

virtual void	EvaluateSamplesAtIndex (RixBXTransportTrait transportTrait, RixBXLobeTraits const &lobesWanted, RixRNG rng, int index, int numSamples, RixBXLobeTraits lobesEvaluated, RtVector3 const directions, RixBXLobeWeights &weights, float forwardPdfs, float *reversePdfs)=0
	Do multiple evals at a single shading point. More...

virtual void	Release ()
	Release does any cleanup that might be needed (often none and the base implementation is fine) and then calls the base implementation. More...

Protected Attributes
RixShadingContext const *	shadingCtx

RixBxdfFactory *	bxdfFactory

Detailed Description

The RixBxdf interface is a shading plugin responsible for creating a RixBxdf from the the ShadingContext and the set of connected patterns.

The RixBxdf interface characterizes the light-scattering behavior at positions in a material.

Integrators 'drive' Bxdf subclasses by:

invoking RixBxdfFactory::Begin to obtain a RixBxdf parameterized by the Bxdf's potentially varying input parameters. BxdfFactory is expected to invoke EvalParam for those parameters that pertain to the integration request.
requesting the Bxdf to generate samples of the bxdf function to facilitate integrating a subset of the general light transport solution.
requesting the Bxdf to evaluate samples associated with a particular phase of integration.

To support several integrator-optimization strategies (diverse sampling frequencies, baking, etc.), we characterize a Bxdf as a collection of individually sampled lobes. Integrators may request samples from a subset of lobes and obtain insight into the general characteristics of each component.

Execution model:

there is one instance of a RixBxdfFactory per bound RiBxdf (RIB) request.
a single RixBxdfFactory may be active in multiple threads simultaneously.
the context for a per-thread execution is signaled via Begin/End. The RixBxdfFactory should stash state in the RixBxdf object and consider that the lifetime of a RixBxdf instance is under control of the integrator. Generally integrators should attempt to minimize the number of live RixBxdf objects but may nonetheless require a large number. For this reason, the RixBxdf instances should attempt to minimize memory consumption and construct/deconstruct costs.
the primary RixBxdf entrypoints operate on a collection of shading points in order to reasonably maximize shading coherency and support SIMD computation. Integrators rely on the RixBxdf's ability to generate and evaluate a sample across the entire collection of points. Should an integrator require multiple samples at the shading points, it will invoke the single-sample methods multiple times, taking care to initialize the random number contexts appropriately. Sample evaluation may be performed in a 1 sample all points variant - EvaluateSample, and a 1 point n samples variant via EvaluateSamplesAtIndex). Generation however is constrained to 1 sample n points. Evaluation typically has different requirements (eg. for making connections in a bidirectional integrator), whereas generation typically benefits from being performed all points at once.

Member Enumeration Documentation

enum RixBxdf::BxdfProperty

See Also: GetProperty

Enumerator
k_Albedo	RtColorRGB.
k_MaterialIor	float

Constructor & Destructor Documentation

RixBxdf::RixBxdf	(	RixShadingContext const *	sCtx,
		RixBxdfFactory *	factory
	)

inline

virtual RixBxdf::~RixBxdf ( )

inlinevirtual

Member Function Documentation

virtual bool RixBxdf::EmitLocal ( RtColorRGB * result)

pure virtual

Used for baked, pre-integrated, indirect results.

A trivial implementation with no local emission should simply return false, indicating to the integrator that 'result' is untouched and that the integrator should not do anything with the results. For bxdfs that do have local emission, they should return true and write shadingCtx->numPts colors to the 'result' array. The integrator will then include the returned colors in the direct lighting for the geometry.

Parameters

[out] result Local emission color buffer

virtual void RixBxdf::EvaluateSample	(	RixBXTransportTrait	transportTrait,
		RixBXLobeTraits const *	lobesWanted,
		RixRNG *	rng,
		RixBXLobeTraits *	lobesEvaluated,
		RtVector3 const *	directions,
		RixBXLobeWeights &	weights,
		float *	forwardPdfs,
		float *	reversePdfs
	)

pure virtual

Bxdf is expected to evaluate itself subject to the lobesWanted request.

In addition to directions, the ShadingContext variables (primarily Vn, Nn, Tn) must be consulted.

The lobesEvaluated output can be set to indicate invalid conditions. If and only if the bxdf is unable to satisfy the request, then lobesEvaluated should be set to invalid using SetValid(false). For example, if the lobesWanted argument requests a specific lobe (e.g., diffuse reflection) that the Bxdf does not support (for instance, that Bxdf only supports glossy reflections), then lobesEvaluated should be marked invalid. However, if it is possible to evaluate the request, then lobesEvaluated should not be marked as invalid (and should instead be set to the evaluated lobe for each point in the ShadingContext). For valid samples, usually the pdf will be non-zero but the weight may be set to 0 if there is no surface response for the given directions. In some cases, it is appropriate to set the pdf to zero when a given sample could never have been generated (for example, if the sample direction is below the horizon of the surface for a purely reflective surface).

This function can assume that the input directions are normalized.

Parameters

[in]	transportTrait	The subset of light transport to consider
[in]	lobesWanted	Specify lobes for evaluation
[in]	rng	Random number generator
[out]	lobesEvaluated	Evaluated lobe for each point in the ShadingContext
[out]	directions	Generated sample direction for each point (normalized)
[out]	weights	Generated lobe weights for each point
[out]	forwardPdfs	Generated forward PDF for each point
[out]	reversePdfs	Generated reverse PDF for each point

Implemented in RixNullBxdf.

virtual void RixBxdf::EvaluateSamplesAtIndex	(	RixBXTransportTrait	transportTrait,
		RixBXLobeTraits const &	lobesWanted,
		RixRNG *	rng,
		int	index,
		int	numSamples,
		RixBXLobeTraits *	lobesEvaluated,
		RtVector3 const *	directions,
		RixBXLobeWeights &	weights,
		float *	forwardPdfs,
		float *	reversePdfs
	)

pure virtual

Do multiple evals at a single shading point.

Also see the documentation above for EvaluateSample().

Parameters

[in]	transportTrait	The subset of light transport to consider
[in]	lobesWanted	Specify lobes for evaluation
[in]	rng	Random number generator
[in]	index	Shading point index
[in]	numSamples	Number of evaluations at this point
[out]	lobesEvaluated	Evaluated lobe for each point in the ShadingContext
[out]	directions	Generated sample direction for each point (normalized)
[out]	weights	Generated lobe weights for each point
[out]	forwardPdfs	Generated forward PDF for each point
[out]	reversePdfs	Generated reverse PDF for each point

Implemented in RixNullBxdf.

virtual void RixBxdf::GenerateSample	(	RixBXTransportTrait	transportTrait,
		RixBXLobeTraits const *	lobesWanted,
		RixRNG *	rng,
		RixBXLobeSampled *	lobesSampled,
		RtVector3 *	directions,
		RixBXLobeWeights &	weights,
		float *	forwardPdfs,
		float *	reversePdfs,
		RtColorRGB *	compTrans = `NULL`
	)

pure virtual

Generate sample data for each point.

A Bxdf is expected to generate a sample direction and lobe weights for each point in the ShadingContext (shadingCtx). Bxdfs must respect the transportTrait and lobesWanted request and indicate which class of lobe is associated with each sample by setting lobesSampled for each generated sample. If and only if the bxdf is unable to generate a requested sample, then lobesSampled should be marked as invalid using SetValid(false). For example, if the lobesWanted argument requests a specific lobe (e.g., diffuse reflection) that the Bxdf does not support (e.g. because it only supports glossy reflection), then lobesSampled should be marked as invalid. However, if it is possible to generate the requested samples, then lobesSampled should instead be set to the sampled lobe for each point in the ShadingContext. Note that it is possible for the returned lobe weights to be set to zero for one or more of the points in the ShadingContext when there is no surface response for the sampled directions, although usually the returned pdfs will be non-zero. The pdf should be set to zero only if the probability of the Bxdf model generating a given sample is zero (see the documentation for EvaluateSample() for an example where setting the pdf to zero is appropriate).

The generated sample directions must be normalized.

Bxdf can (but not expected to) return a colored transmission value in "compTrans" which is used to generate "alpha" in the integrator. The main purpose of this "alpha" is compositing. Bxdf should check against null pointer before setting compTrans. If compTrans is non zero (caller of GenerateSample is responsible for memory allocation of compTrans) and bxdf does not set compTrans, the integrator is responsible for setting compTrans to (0,0,0) by default.

Parameters

[in]	transportTrait	The subset of light transport to consider.
[in]	lobesWanted	Specify lobes for evaluation.
[in]	rng	Random number generator.
[out]	lobesSampled	Sampled lobe for each point in the ShadingContext.
[out]	directions	Generated sample direction for each point (normalized).
[out]	weights	Generated lobe weights for each point.
[out]	forwardPdfs	Generated forward PDF for each point.
[out]	reversePdfs	Generated reverse PDF for each point.
[out]	compTrans	Generated color transmission for compositing.

Implemented in RixNullBxdf.

virtual void RixBxdf::GetAggregateLobeTraits ( RixBXLobeTraits * t)

pure virtual

The types of samples this BxdfEvaluator can generate.

Referenced by GetAllLobeTraits().

PRMAN_INLINE RixBXLobeTraits RixBxdf::GetAllLobeTraits ( )

inline

References GetAggregateLobeTraits().

RixBxdfFactory* RixBxdf::GetBxdfFactory ( )

inline

References bxdfFactory.

virtual RixBXEvaluateDomain RixBxdf::GetEvaluateDomain ( )

pure virtual

The domain over which this Bxdf evaluates samples.

Note that it may Generate discrete samples in any direction, this only tells where incoming samples could Evaluate to non-zero.

Implemented in RixNullBxdf.

virtual RixSCDetail RixBxdf::GetProperty	(	BxdfProperty	property,
		void const **	result
	)		const

pure virtual

Get material property Bxdfs can be queried for general material properties to facilitate integration tasks.

Bxdfs should return k_RixSCInvalidDetail if a particular property is unsupported. If a property is supported Bxdf should return k_RixSCUniform or k_RixSCVarying according to the detail of the result. A trivial implementation that supports no properties of any sort should simply return k_RixSCInvalidDetail.

Parameters

[in]	property	Property to query
[out]	result	Results

RixShadingContext const* RixBxdf::GetShadingCtx ( )

inline

References shadingCtx.

virtual void RixBxdf::Release ( )

inlinevirtual

Release does any cleanup that might be needed (often none and the base implementation is fine) and then calls the base implementation.

A RixBxdf that contains another RixBxdf would need to call Release on its child as part of its own Release.

References bxdfFactory, and RixBxdfFactory::EndScatter().

Member Data Documentation

RixBxdfFactory* RixBxdf::bxdfFactory

protected

Referenced by GetBxdfFactory(), and Release().

RixShadingContext const* RixBxdf::shadingCtx

protected

Referenced by GetShadingCtx().

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

RixBxdf.h

Public Types

Public Member Functions

Protected Attributes

Detailed Description

Member Enumeration Documentation

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation