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more accurate Fresnel reflectance computations involving conductors

metadata
Wenzel Jakob 2012-12-04 01:09:29 -05:00
parent b90faa309b
commit 4506e9daf7
7 changed files with 226 additions and 62 deletions
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8
include/mitsuba/core/spectrum.h
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@ -493,6 +493,14 @@ public:
return value;
}
/// Component-wise square root
inline TSpectrum safe_sqrt() const {
TSpectrum value;
for (int i=0; i<N; i++)
value.s[i] = math::safe_sqrt(s[i]);
return value;
}
/// Component-wise exponentation
inline TSpectrum exp() const {
TSpectrum value;

89
include/mitsuba/core/util.h
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@ -507,22 +507,99 @@ inline Float fresnelDielectricExt(Float cosThetaI, Float eta) { Float cosThetaT;
return fresnelDielectricExt(cosThetaI, cosThetaT, eta); }
/**
* \brief Calculates the unpolarized fresnel reflection coefficient
* at a planar interface between vacuum and a conductor.
* \brief Calculates the unpolarized Fresnel reflection coefficient
* at a planar interface having a complex-valued relative index of
* refraction (approximate scalar version)
*
* The implementation of this function relies on a simplified expression
* that becomes increasingly accurate as k grows.
*
* The name of this function is a slight misnomer, since it supports
* the general case of a complex-valued relative index of refraction
* (rather than being restricted to conductors)
*
* \param cosThetaI
* Cosine of the angle between the normal and the incident ray
* \param eta
* Real refractive index (wavelength-dependent)
* Relative refractive index (real component)
* \param k
* Imaginary refractive index (wavelength-dependent)
* Relative refractive index (imaginary component)
* \ingroup libpython
*/
extern MTS_EXPORT_CORE Spectrum fresnelConductor(Float cosThetaI,
extern MTS_EXPORT_CORE Float fresnelConductorApprox(Float cosThetaI,
Float eta, Float k);
/**
* \brief Calculates the unpolarized Fresnel reflection coefficient
* at a planar interface having a complex-valued relative index of
* refraction (approximate vectorized version)
*
* The implementation of this function relies on a simplified expression
* that becomes increasingly accurate as k grows.
*
* The name of this function is a slight misnomer, since it supports
* the general case of a complex-valued relative index of refraction
* (rather than being restricted to conductors)
*
* \param cosThetaI
* Cosine of the angle between the normal and the incident ray
* \param eta
* Relative refractive index (real component)
* \param k
* Relative refractive index (imaginary component)
* \ingroup libpython
*/
extern MTS_EXPORT_CORE Spectrum fresnelConductorApprox(Float cosThetaI,
const Spectrum &eta, const Spectrum &k);
/**
* \brief Calculates the diffuse unpolarized fresnel reflectance of
* \brief Calculates the unpolarized Fresnel reflection coefficient
* at a planar interface having a complex-valued relative index of
* refraction (accurate scalar version)
*
* The implementation of this function computes the exact unpolarized
* Fresnel reflectance for a complex index of refraction change.
*
* The name of this function is a slight misnomer, since it supports
* the general case of a complex-valued relative index of refraction
* (rather than being restricted to conductors)
*
* \param cosThetaI
* Cosine of the angle between the normal and the incident ray
* \param eta
* Relative refractive index (real component)
* \param k
* Relative refractive index (imaginary component)
* \ingroup libpython
*/
extern MTS_EXPORT_CORE Float fresnelConductorExact(Float cosThetaI,
Float eta, Float k);
/**
* \brief Calculates the unpolarized Fresnel reflection coefficient
* at a planar interface having a complex-valued relative index of
* refraction (accurate vectorized version)
*
* The implementation of this function computes the exact unpolarized
* Fresnel reflectance for a complex index of refraction change.
*
* The name of this function is a slight misnomer, since it supports
* the general case of a complex-valued relative index of refraction
* (rather than being restricted to conductors)
*
* \param cosThetaI
* Cosine of the angle between the normal and the incident ray
* \param eta
* Relative refractive index (real component)
* \param k
* Relative refractive index (imaginary component)
* \ingroup libpython
*/
extern MTS_EXPORT_CORE Spectrum fresnelConductorExact(Float cosThetaI,
const Spectrum &eta, const Spectrum &k);
/**
* \brief Calculates the diffuse unpolarized Fresnel reflectance of
* a dielectric material (sometimes referred to as "Fdr").
*
* This value quantifies what fraction of diffuse incident illumination

44
src/bsdfs/conductor.cpp
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@ -20,6 +20,7 @@
#include <mitsuba/core/fresolver.h>
#include <mitsuba/hw/basicshader.h>
#include <boost/algorithm/string.hpp>
#include "ior.h"
MTS_NAMESPACE_BEGIN
@ -29,11 +30,12 @@ MTS_NAMESPACE_BEGIN
* \parameters{
* \parameter{material}{\String}{Name of a material preset, see
* \tblref{conductor-iors}.\!\default{\texttt{Cu} / copper}}
* \parameter{eta}{\Spectrum}{Real part of the material's index
* of refraction \default{based on the value of \texttt{material}}}
* \parameter{k}{\Spectrum}{Imaginary part of the material's index of
* refraction, also known as absorption coefficient.
* \default{based on the value of \texttt{material}}}
* \parameter{eta, k}{\Spectrum}{Real and imaginary components of the material's index of
* refraction \default{based on the value of \texttt{material}}}
* \parameter{extEta}{\Float\Or\String}{
* Real-valued index of refraction of the surrounding dielectric,
* or a material name of a dielectric \default{\code{air}}
* }
* \parameter{specular\showbreak Reflectance}{\Spectrum\Or\Texture}{Optional
* factor that can be used to modulate the specular reflection component. Note
* that for physical realism, this parameter should never be touched. \default{1.0}}
@ -154,21 +156,23 @@ public:
m_specularReflectance = new ConstantSpectrumTexture(
props.getSpectrum("specularReflectance", Spectrum(1.0f)));
std::string material = props.getString("material", "Cu");
std::string materialName = props.getString("material", "Cu");
Spectrum materialEta, materialK;
if (boost::to_lower_copy(material) == "none") {
materialEta = Spectrum(0.0f);
materialK = Spectrum(1.0f);
Spectrum intEta, intK;
if (boost::to_lower_copy(materialName) == "none") {
intEta = Spectrum(0.0f);
intK = Spectrum(1.0f);
} else {
materialEta.fromContinuousSpectrum(InterpolatedSpectrum(
fResolver->resolve("data/ior/" + material + ".eta.spd")));
materialK.fromContinuousSpectrum(InterpolatedSpectrum(
fResolver->resolve("data/ior/" + material + ".k.spd")));
intEta.fromContinuousSpectrum(InterpolatedSpectrum(
fResolver->resolve("data/ior/" + materialName + ".eta.spd")));
intK.fromContinuousSpectrum(InterpolatedSpectrum(
fResolver->resolve("data/ior/" + materialName + ".k.spd")));
}
m_eta = props.getSpectrum("eta", materialEta);
m_k = props.getSpectrum("k", materialK);
Float extEta = lookupIOR(props, "extEta", "air");
m_eta = props.getSpectrum("eta", intEta) / extEta;
m_k = props.getSpectrum("k", intK) / extEta;
}
SmoothConductor(Stream *stream, InstanceManager *manager)
@ -229,7 +233,7 @@ public:
return Spectrum(0.0f);
return m_specularReflectance->eval(bRec.its) *
fresnelConductor(Frame::cosTheta(bRec.wi), m_eta, m_k);
fresnelConductorExact(Frame::cosTheta(bRec.wi), m_eta, m_k);
}
Float pdf(const BSDFSamplingRecord &bRec, EMeasure measure) const {
@ -260,7 +264,7 @@ public:
bRec.eta = 1.0f;
return m_specularReflectance->eval(bRec.its) *
fresnelConductor(Frame::cosTheta(bRec.wi), m_eta, m_k);
fresnelConductorExact(Frame::cosTheta(bRec.wi), m_eta, m_k);
}
Spectrum sample(BSDFSamplingRecord &bRec, Float &pdf, const Point2 &sample) const {
@ -277,7 +281,7 @@ public:
pdf = 1;
return m_specularReflectance->eval(bRec.its) *
fresnelConductor(Frame::cosTheta(bRec.wi), m_eta, m_k);
fresnelConductorExact(Frame::cosTheta(bRec.wi), m_eta, m_k);
}
Float getRoughness(const Intersection &its, int component) const {
@ -320,7 +324,7 @@ public:
m_specularReflectanceShader = renderer->registerShaderForResource(m_specularReflectance.get());
/* Compute the reflectance at perpendicular incidence */
m_R0 = fresnelConductor(1.0f, eta, k);
m_R0 = fresnelConductorExact(1.0f, eta, k);
m_alpha = 0.4f;
}

50
src/bsdfs/roughconductor.cpp
View File

@ -20,6 +20,7 @@
#include <mitsuba/render/bsdf.h>
#include <mitsuba/hw/basicshader.h>
#include "microfacet.h"
#include "ior.h"
MTS_NAMESPACE_BEGIN
@ -32,15 +33,15 @@ MTS_NAMESPACE_BEGIN
* used to model the surface roughness.
* \begin{enumerate}[(i)]
* \item \code{beckmann}: Physically-based distribution derived from
* Gaussian random surfaces. This is the default.
* Gaussian random surfaces. This is the default.\vspace{-1mm}
* \item \code{ggx}: New distribution proposed by
* Walter et al. \cite{Walter07Microfacet}, which is meant to better handle
* the long tails observed in measurements of ground surfaces.
* Renderings with this distribution may converge slowly.
* Renderings with this distribution may converge slowly.\vspace{-1mm}
* \item \code{phong}: Classical $\cos^p\theta$ distribution.
* Due to the underlying microfacet theory,
* the use of this distribution here leads to more realistic
* behavior than the separately available \pluginref{phong} plugin.
* behavior than the separately available \pluginref{phong} plugin.\vspace{-1mm}
* \item \code{as}: Anisotropic Phong-style microfacet distribution proposed by
* Ashikhmin and Shirley \cite{Ashikhmin2005Anisotropic}.\vspace{-3mm}
* \end{enumerate}
@ -59,11 +60,12 @@ MTS_NAMESPACE_BEGIN
* }
* \parameter{material}{\String}{Name of a material preset, see
* \tblref{conductor-iors}.\!\default{\texttt{Cu} / copper}}
* \parameter{eta}{\Spectrum}{Real part of the material's index
* of refraction \default{based on the value of \texttt{material}}}
* \parameter{k}{\Spectrum}{Imaginary part of the material's index of
* refraction (the absorption coefficient).
* \default{based on \texttt{material}}}
* \parameter{eta, k}{\Spectrum}{Real and imaginary components of the material's index of
* refraction \default{based on the value of \texttt{material}}}
* \parameter{extEta}{\Float\Or\String}{
* Real-valued index of refraction of the surrounding dielectric,
* or a material name of a dielectric \default{\code{air}}
* }
* \parameter{specular\showbreak Reflectance}{\Spectrum\Or\Texture}{Optional
* factor that can be used to modulate the specular reflection component. Note
* that for physical realism, this parameter should never be touched. \default{1.0}}
@ -158,21 +160,23 @@ public:
m_specularReflectance = new ConstantSpectrumTexture(
props.getSpectrum("specularReflectance", Spectrum(1.0f)));
std::string material = props.getString("material", "Cu");
Spectrum materialEta, materialK;
std::string materialName = props.getString("material", "Cu");
if (boost::to_lower_copy(material) == "none") {
materialEta = Spectrum(0.0f);
materialK = Spectrum(1.0f);
Spectrum intEta, intK;
if (boost::to_lower_copy(materialName) == "none") {
intEta = Spectrum(0.0f);
intK = Spectrum(1.0f);
} else {
materialEta.fromContinuousSpectrum(InterpolatedSpectrum(
fResolver->resolve("data/ior/" + material + ".eta.spd")));
materialK.fromContinuousSpectrum(InterpolatedSpectrum(
fResolver->resolve("data/ior/" + material + ".k.spd")));
intEta.fromContinuousSpectrum(InterpolatedSpectrum(
fResolver->resolve("data/ior/" + materialName + ".eta.spd")));
intK.fromContinuousSpectrum(InterpolatedSpectrum(
fResolver->resolve("data/ior/" + materialName + ".k.spd")));
}
m_eta = props.getSpectrum("eta", materialEta);
m_k = props.getSpectrum("k", materialK);
Float extEta = lookupIOR(props, "extEta", "air");
m_eta = props.getSpectrum("eta", intEta) / extEta;
m_k = props.getSpectrum("k", intK) / extEta;
m_distribution = MicrofacetDistribution(
props.getString("distribution", "beckmann")
@ -262,7 +266,7 @@ public:
return Spectrum(0.0f);
/* Fresnel factor */
const Spectrum F = fresnelConductor(dot(bRec.wi, H), m_eta, m_k);
const Spectrum F = fresnelConductorExact(dot(bRec.wi, H), m_eta, m_k);
/* Smith's shadow-masking function */
const Float G = m_distribution.G(bRec.wi, bRec.wo, H, alphaU, alphaV);
@ -324,7 +328,7 @@ public:
if (Frame::cosTheta(bRec.wo) <= 0)
return Spectrum(0.0f);
const Spectrum F = fresnelConductor(dot(bRec.wi, m),
const Spectrum F = fresnelConductorExact(dot(bRec.wi, m),
m_eta, m_k);
Float numerator = m_distribution.eval(m, alphaU, alphaV)
@ -367,7 +371,7 @@ public:
if (Frame::cosTheta(bRec.wo) <= 0)
return Spectrum(0.0f);
const Spectrum F = fresnelConductor(dot(bRec.wi, m),
const Spectrum F = fresnelConductorExact(dot(bRec.wi, m),
m_eta, m_k);
Float numerator = m_distribution.eval(m, alphaU, alphaV)
@ -460,7 +464,7 @@ public:
m_alphaVShader = renderer->registerShaderForResource(m_alphaV.get());
/* Compute the reflectance at perpendicular incidence */
m_R0 = fresnelConductor(1.0f, eta, k);
m_R0 = fresnelConductorExact(1.0f, eta, k);
}
bool isComplete() const {

80
src/libcore/util.cpp
View File

@ -586,18 +586,84 @@ Float fresnelDielectricExt(Float cosThetaI_, Float &cosThetaT_, Float eta) {
return 0.5f * (Rs * Rs + Rp * Rp);
}
Spectrum fresnelConductor(Float cosThetaI, const Spectrum &eta, const Spectrum &k) {
Spectrum tmp = (eta*eta + k*k) * (cosThetaI * cosThetaI);
Float fresnelConductorApprox(Float cosThetaI, Float eta, Float k) {
Float cosThetaI2 = cosThetaI*cosThetaI;
Spectrum rParl2 = (tmp - (eta * (2.0f * cosThetaI)) + Spectrum(1.0f))
/ (tmp + (eta * (2.0f * cosThetaI)) + Spectrum(1.0f));
Float tmp = (eta*eta + k*k) * cosThetaI2;
Float Rp2 = (tmp - (eta * (2 * cosThetaI)) + 1)
/ (tmp + (eta * (2 * cosThetaI)) + 1);
Float tmpF = eta*eta + k*k;
Float Rs2 = (tmpF - (eta * (2 * cosThetaI)) + cosThetaI2) /
(tmpF + (eta * (2 * cosThetaI)) + cosThetaI2);
return 0.5f * (Rp2 + Rs2);
}
Spectrum fresnelConductorApprox(Float cosThetaI, const Spectrum &eta, const Spectrum &k) {
Float cosThetaI2 = cosThetaI*cosThetaI;
Spectrum tmp = (eta*eta + k*k) * cosThetaI2;
Spectrum Rp2 = (tmp - (eta * (2 * cosThetaI)) + Spectrum(1.0f))
/ (tmp + (eta * (2 * cosThetaI)) + Spectrum(1.0f));
Spectrum tmpF = eta*eta + k*k;
Spectrum rPerp2 = (tmpF - (eta * (2.0f * cosThetaI)) + Spectrum(cosThetaI*cosThetaI)) /
(tmpF + (eta * (2.0f * cosThetaI)) + Spectrum(cosThetaI*cosThetaI));
Spectrum Rs2 = (tmpF - (eta * (2 * cosThetaI)) + Spectrum(cosThetaI2)) /
(tmpF + (eta * (2 * cosThetaI)) + Spectrum(cosThetaI2));
return (rParl2 + rPerp2) / 2.0f;
return 0.5f * (Rp2 + Rs2);
}
Float fresnelConductorExact(Float cosThetaI, Float eta, Float k) {
/* Modified from "Optics" by K.D. Moeller, University Science Books, 1988 */
Float cosThetaI2 = cosThetaI*cosThetaI,
sinThetaI2 = 1-cosThetaI2,
sinThetaI4 = sinThetaI2*sinThetaI2;
Float temp1 = eta*eta - k*k - sinThetaI2,
a2pb2 = math::safe_sqrt(temp1*temp1 + 4*k*k*eta*eta),
a = math::safe_sqrt(0.5f * (a2pb2 + temp1));
Float term1 = a2pb2 + cosThetaI2,
term2 = 2*a*cosThetaI;
Float Rs2 = (term1 - term2) / (term1 + term2);
Float term3 = a2pb2*cosThetaI2 + sinThetaI4,
term4 = term2*sinThetaI2;
Float Rp2 = Rs2 * (term3 - term4) / (term3 + term4);
return 0.5f * (Rp2 + Rs2);
}
Spectrum fresnelConductorExact(Float cosThetaI, const Spectrum &eta, const Spectrum &k) {
/* Modified from "Optics" by K.D. Moeller, University Science Books, 1988 */
Float cosThetaI2 = cosThetaI*cosThetaI,
sinThetaI2 = 1-cosThetaI2,
sinThetaI4 = sinThetaI2*sinThetaI2;
Spectrum temp1 = eta*eta - k*k - Spectrum(sinThetaI2),
a2pb2 = (temp1*temp1 + k*k*eta*eta*4).safe_sqrt(),
a = ((a2pb2 + temp1) * 0.5f).safe_sqrt();
Spectrum term1 = a2pb2 + Spectrum(cosThetaI2),
term2 = a*(2*cosThetaI);
Spectrum Rs2 = (term1 - term2) / (term1 + term2);
Spectrum term3 = a2pb2*cosThetaI2 + Spectrum(sinThetaI4),
term4 = term2*sinThetaI2;
Spectrum Rp2 = Rs2 * (term3 - term4) / (term3 + term4);
return 0.5f * (Rp2 + Rs2);
}
Vector reflect(const Vector &wi, const Normal &n) {

14
src/libpython/core.cpp
View File

@ -79,10 +79,10 @@ void initializeFramework() {
if (GetModuleHandleExA(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS |
GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT, (LPCSTR) &initializeFramework, &hm)) {
std::vector<WCHAR> lpFilename(MAX_PATH);
// Try to get the path with the default MAX_PATH length (260 chars)
DWORD nSize = GetModuleFileNameW(hm, &lpFilename[0], MAX_PATH);
// Adjust the buffer size in case if was too short
while (nSize == lpFilename.size()) {
lpFilename.resize(nSize * 2);
@ -1261,11 +1261,19 @@ void export_core() {
.staticmethod("glOrthographic")
.staticmethod("fromFrame");
Float (*fresnelConductorApprox1)(Float, Float, Float) = &fresnelConductorApprox;
Float (*fresnelConductorExact1)(Float, Float, Float) = &fresnelConductorExact;
Spectrum (*fresnelConductorApprox2)(Float, const Spectrum &, const Spectrum &) = &fresnelConductorApprox;
Spectrum (*fresnelConductorExact2)(Float, const Spectrum &, const Spectrum &) = &fresnelConductorExact;
/* Functions from utility.h */
bp::def("fresnelDielectric", &fresnelDielectric);
bp::def("fresnelDielectricExt", &fresnelDielectricExt1);
bp::def("fresnelDielectricExt", &fresnelDielectricExt2);
bp::def("fresnelConductor", &fresnelConductor, BP_RETURN_VALUE);
bp::def("fresnelConductorApprox", fresnelConductorApprox1, BP_RETURN_VALUE);
bp::def("fresnelConductorApprox", fresnelConductorApprox2, BP_RETURN_VALUE);
bp::def("fresnelConductorExact", fresnelConductorExact1, BP_RETURN_VALUE);
bp::def("fresnelConductorExact", fresnelConductorExact2, BP_RETURN_VALUE);
bp::def("fresnelDiffuseReflectance", &fresnelDiffuseReflectance);
bp::def("reflect", &reflect);
bp::def("refract", &refract1);

3
src/mtsgui/mainwindow.cpp
View File

@ -1478,9 +1478,6 @@ void MainWindow::on_actionExportImage_triggered() {
}
void MainWindow::onExportDialogClose(int reason) {
int currentIndex = ui->tabBar->currentIndex();
SceneContext *ctx = m_context[currentIndex];
QSettings settings;
QFileDialog *dialog = static_cast<QFileDialog *>(sender());
m_currentChild = NULL;