Trowbridge-Reitz distribution (GGX). See the original paper by Trowbridge et al. [16]. The paper "Microfacet Models for Refraction through Rough Surfaces" by Walter et al. [18] provides a nice explanation, too. More...

#include <TrowbridgeReitz.h>

Inheritance diagram for ph::TrowbridgeReitz:

Public Member Functions
	TrowbridgeReitz (EMaskingShadowing maskingShadowingType)

std::array< real, 2 >	getAlphas (const SurfaceHit &X) const override=0

real	lambda (const SurfaceHit &X, const math::Vector3R &N, const math::Vector3R &H, const math::Vector3R &unitDir, const std::array< real, 2 > &alphas) const override=0
	The \( \Lambda \left( a \right) \) function that appears in the masking-shadowing term. For isotropic distributions, the variable \( a \) is normally calculated as \( a = \frac{1}{\alpha \tan \left( \theta \right)} \), where \( \frac{1}{\tan \left( \theta \right)} \) is the slope of the unit direction `unitDir` (with respect to the macrosurface normal `N`. For anisotropic distributions, see the implementation of `AnisoTrowbridgeReitz` as an example for calculating \( a \) from the parameters.

real	distribution (const SurfaceHit &X, const math::Vector3R &N, const math::Vector3R &H) const override=0
	Distribution of the microfacet normal. The \( D \) term. Also commonly knwon as the NDF (normal distribution function). This term is defined in the half-angle/microfacet space (the angle between `N` and `H`) unless otherwise noted.

void	sampleH (const SurfaceHit &X, const math::Vector3R &N, const std::array< real, 2 > &sample, math::Vector3R *out_H) const override=0
	Generate a microfacet normal `H` for the distribution. This samples all possible `H` vectors for the distribution.

void	sampleVisibleH (const SurfaceHit &X, const math::Vector3R &N, const math::Vector3R &V, const std::array< real, 2 > &sample, math::Vector3R *out_H) const override
	Same as `sampleH()`, but tries to take geometry term into consideration. This samples only potentially visible `H` vectors for the distribution. If unable to fully or partly incorporate visibility information from the geometry term, this method will fallback to `sampleH()`.

lta::PDF	pdfSampleVisibleH (const SurfaceHit &X, const math::Vector3R &N, const math::Vector3R &H, const math::Vector3R &V) const override

Public Member Functions inherited from ph::ShapeInvariantMicrofacet
	ShapeInvariantMicrofacet (EMaskingShadowing maskingShadowingType)

real	geometry (const SurfaceHit &X, const math::Vector3R &N, const math::Vector3R &H, const math::Vector3R &L, const math::Vector3R &V) const override
	Masking and shadowing due to nearby microfacets. The \( G \) term.

lta::PDF	pdfSampleH (const SurfaceHit &X, const math::Vector3R &N, const math::Vector3R &H) const override

Public Member Functions inherited from ph::Microfacet
virtual	~Microfacet ()=default

Additional Inherited Members
Protected Member Functions inherited from ph::ShapeInvariantMicrofacet
real	smithG1 (real lambdaValue) const

real	empiricalPhiCorrelation (const SurfaceHit &X, const math::Vector3R &L, const math::Vector3R &V) const

real	projectedDistribution (const SurfaceHit &X, const math::Vector3R &N, const math::Vector3R &H) const

real	visibleDistribution (const SurfaceHit &X, const math::Vector3R &N, const math::Vector3R &H, const math::Vector3R &V) const

Static Protected Member Functions inherited from ph::Microfacet
static bool	isSidednessAgreed (real NoD, real HoD)

static bool	isSidednessAgreed (real NoL, real NoV, real HoL, real HoV)

Protected Attributes inherited from ph::ShapeInvariantMicrofacet
EMaskingShadowing	m_maskingShadowingType

Detailed Description

Trowbridge-Reitz distribution (GGX). See the original paper by Trowbridge et al. [16]. The paper "Microfacet Models for Refraction through Rough Surfaces" by Walter et al. [18] provides a nice explanation, too.

Constructor & Destructor Documentation

◆ TrowbridgeReitz()

ph::TrowbridgeReitz::TrowbridgeReitz ( EMaskingShadowing maskingShadowingType )

explicit

Member Function Documentation

◆ distribution()

real ph::TrowbridgeReitz::distribution	(	const SurfaceHit &	X,
		const math::Vector3R &	N,
		const math::Vector3R &	H ) const

overridepure virtual

Distribution of the microfacet normal. The \( D \) term. Also commonly knwon as the NDF (normal distribution function). This term is defined in the half-angle/microfacet space (the angle between N and H) unless otherwise noted.

Parameters

H	The microfacet normal.

Remarks: Do not treat this term as the probability density of microfacet normal over solid angle.

Implements ph::ShapeInvariantMicrofacet.

Implemented in ph::AnisoTrowbridgeReitz, and ph::IsoTrowbridgeReitz.

◆ getAlphas()

std::array< real, 2 > ph::TrowbridgeReitz::getAlphas ( const SurfaceHit & X ) const

overridepure virtual

Returns: \( \left( \alpha_u, \alpha_v \right) \) in the U and V directions of the macrosirface parametrization. Guaranteed to have \( \alpha_u = \alpha_v \) for an isotropic distribution.

Implements ph::ShapeInvariantMicrofacet.

Implemented in ph::AnisoTrowbridgeReitz, ph::IsoTrowbridgeReitz, ph::IsoTrowbridgeReitzConstant, and ph::IsoTrowbridgeReitzTextured.

◆ lambda()

real ph::TrowbridgeReitz::lambda	(	const SurfaceHit &	X,
		const math::Vector3R &	N,
		const math::Vector3R &	H,
		const math::Vector3R &	unitDir,
		const std::array< real, 2 > &	alphas ) const

overridepure virtual

The \( \Lambda \left( a \right) \) function that appears in the masking-shadowing term. For isotropic distributions, the variable \( a \) is normally calculated as \( a = \frac{1}{\alpha \tan \left( \theta \right)} \), where \( \frac{1}{\tan \left( \theta \right)} \) is the slope of the unit direction unitDir (with respect to the macrosurface normal N. For anisotropic distributions, see the implementation of AnisoTrowbridgeReitz as an example for calculating \( a \) from the parameters.

Note: This method does not handle sidedness agreement.

Implements ph::ShapeInvariantMicrofacet.

Implemented in ph::AnisoTrowbridgeReitz, and ph::IsoTrowbridgeReitz.

◆ pdfSampleVisibleH()

lta::PDF ph::TrowbridgeReitz::pdfSampleVisibleH	(	const SurfaceHit &	X,
		const math::Vector3R &	N,
		const math::Vector3R &	H,
		const math::Vector3R &	V ) const

overridevirtual

Returns: PDF of generating the specific microfacet normal H using sampleVisibleH().

Reimplemented from ph::Microfacet.

◆ sampleH()

void ph::TrowbridgeReitz::sampleH	(	const SurfaceHit &	X,
		const math::Vector3R &	N,
		const std::array< real, 2 > &	sample,
		math::Vector3R *	out_H ) const

overridepure virtual

Generate a microfacet normal H for the distribution. This samples all possible H vectors for the distribution.

Parameters

out_H The generated microfacet normal.

Remarks: Use pdfSampleH() for the probability density of sampling the generated H. distribution() is not a probability density of microfacet normal.

Implements ph::ShapeInvariantMicrofacet.

Implemented in ph::AnisoTrowbridgeReitz, and ph::IsoTrowbridgeReitz.

◆ sampleVisibleH()

void ph::TrowbridgeReitz::sampleVisibleH	(	const SurfaceHit &	X,
		const math::Vector3R &	N,
		const math::Vector3R &	V,
		const std::array< real, 2 > &	sample,
		math::Vector3R *	out_H ) const

overridevirtual

Same as sampleH(), but tries to take geometry term into consideration. This samples only potentially visible H vectors for the distribution. If unable to fully or partly incorporate visibility information from the geometry term, this method will fallback to sampleH().

Reimplemented from ph::Microfacet.

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

Source/Core/SurfaceBehavior/Property/TrowbridgeReitz.h
Source/Core/SurfaceBehavior/Property/TrowbridgeReitz.cpp

Public Member Functions

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ TrowbridgeReitz()

Member Function Documentation

◆ distribution()

◆ getAlphas()

◆ lambda()

◆ pdfSampleVisibleH()

◆ sampleH()

◆ sampleVisibleH()