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two-sided coating

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Wenzel Jakob 2011-07-20 00:39:29 +02:00
parent c84be3969a
commit a4acf8b379
3 changed files with 81 additions and 71 deletions
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26
data/tests/test_bsdf.xml
View File

@ -2,6 +2,31 @@
to be tested for consistency. This is done
using the testcase 'test_chisquare' -->
<scene version="0.3.0">
<!-- Test the coating model with a transmissive
+ reflective material -->
<bsdf type="coating">
<rgb name="sigmaA" value="0.1 0.2 0.3"/>
<float name="thickness" value="2"/>
<bsdf type="mixture">
<string name="weights" value=".5 .3"/>
<bsdf type="diffuse">
<rgb name="reflectance" value=".5 0 0"/>
</bsdf>
<bsdf type="difftrans">
<rgb name="transmittance" value="0 .5 0"/>
</bsdf>
</bsdf>
</bsdf>
<!-- Test the coating model with the Hanrahan-Krueger model -->
<bsdf type="coating">
<rgb name="sigmaA" value="0.1 0.2 0.3"/>
<float name="thickness" value="2"/>
<bsdf type="hk"/>
</bsdf>
<!-- Test the Hanrahan-Krueger model with an
isotropic phase function -->
<bsdf type="hk"/>
@ -14,6 +39,7 @@
</phase>
</bsdf>
<!-- Test the smooth diffuse model -->
<bsdf type="diffuse"/>

124
src/bsdfs/coating.cpp
View File

@ -94,6 +94,12 @@ MTS_NAMESPACE_BEGIN
*/
class SmoothCoating : public BSDF {
public:
/// \sa refractTo()
enum EDestination {
EInterior = 0,
EExterior = 1
};
SmoothCoating(const Properties &props)
: BSDF(props) {
/* Specifies the internal index of refraction at the interface */
@ -123,9 +129,6 @@ public:
void configure() {
if (!m_nested)
Log(EError, "A child BSDF instance is required");
if (m_nested->getType() & BSDF::ETransmission)
Log(EError, "Tried to put a smooth coating layer on top of a BSDF "
"with a transmission component -- this is currently not allowed!");
unsigned int extraFlags = 0;
if (!m_sigmaA->isConstant())
@ -135,7 +138,7 @@ public:
for (int i=0; i<m_nested->getComponentCount(); ++i)
m_components.push_back(m_nested->getType(i) | extraFlags);
m_components.push_back(EDeltaReflection | EFrontSide);
m_components.push_back(EDeltaReflection | EFrontSide | EBackSide);
m_usesRayDifferentials = m_nested->usesRayDifferentials()
|| m_sigmaA->usesRayDifferentials();
@ -175,26 +178,21 @@ public:
return Vector(-wi.x, -wi.y, wi.z);
}
/**
* \brief Refraction in local coordinates
*
* To be used when some of the data is already available
*/
inline Vector refract(const Vector &wi, Float eta, Float cosThetaT) const {
return Vector(-eta*wi.x, -eta*wi.y, cosThetaT);
}
/// Refraction in local coordinates (full version)
inline Vector refract(const Vector &wi, Float &F) const {
Float cosThetaI = Frame::cosTheta(wi),
etaI = m_extIOR, etaT = m_intIOR;
/// Refraction in local coordinates
Vector refractTo(EDestination dest,
const Vector &wi, Float &F) const {
Float etaI, etaT;
if (dest == EInterior) {
etaI = m_extIOR;
etaT = m_intIOR;
} else {
etaI = m_intIOR;
etaT = m_extIOR;
}
Float cosThetaI = Frame::cosTheta(wi);
bool entering = cosThetaI > 0.0f;
/* Determine the respective indices of refraction */
if (!entering)
std::swap(etaI, etaT);
/* Using Snell's law, calculate the squared sine of the
angle between the normal and the transmitted ray */
Float eta = etaI / etaT,
@ -210,18 +208,15 @@ public:
/* Compute the Fresnel transmittance */
F = fresnelDielectric(std::abs(Frame::cosTheta(wi)),
cosThetaT, m_extIOR, m_intIOR);
cosThetaT, etaI, etaT);
return Vector(-eta*wi.x, -eta*wi.y,
entering ? -cosThetaT : cosThetaT);
/* Retain the directionality of the vector */
return Vector(eta*wi.x, eta*wi.y,
entering ? cosThetaT : -cosThetaT);
}
}
Spectrum eval(const BSDFQueryRecord &bRec, EMeasure measure) const {
if (Frame::cosTheta(bRec.wi) <= 0 ||
Frame::cosTheta(bRec.wo) <= 0)
return Spectrum(0.0f);
bool sampleSpecular = (bRec.typeMask & EDeltaReflection)
&& (bRec.component == -1 || bRec.component == (int) m_components.size()-1);
bool sampleNested = (bRec.typeMask & m_nested->getType() & BSDF::EAll)
@ -230,29 +225,29 @@ public:
if (measure == EDiscrete && sampleSpecular &&
std::abs(1-dot(reflect(bRec.wi), bRec.wo)) < Epsilon) {
return Spectrum(fresnel(
Frame::cosTheta(bRec.wi), m_extIOR, m_intIOR));
std::abs(Frame::cosTheta(bRec.wi)), m_extIOR, m_intIOR));
} else if (sampleNested) {
Float R12, R21;
BSDFQueryRecord bRec2(bRec);
bRec2.wi = -refract(bRec.wi, R12);
bRec2.wo = -refract(bRec.wo, R21);
BSDFQueryRecord bRecInt(bRec);
bRecInt.wi = refractTo(EInterior, bRec.wi, R12);
bRecInt.wo = refractTo(EInterior, bRec.wo, R21);
if (R12 == 1 || R21 == 1) /* Total internal reflection */
return Spectrum(0.0f);
Float eta = m_extIOR / m_intIOR;
Spectrum result = m_nested->eval(bRec2, measure)
Spectrum result = m_nested->eval(bRecInt, measure)
* ((1-R12) * (1-R21) * eta * eta);
Spectrum sigmaA = m_sigmaA->getValue(bRec.its) * m_thickness;
if (!sigmaA.isZero())
result *= (-sigmaA *
(1/std::abs(Frame::cosTheta(bRec2.wi)) +
1/std::abs(Frame::cosTheta(bRec2.wo)))).exp();
(1/std::abs(Frame::cosTheta(bRecInt.wi)) +
1/std::abs(Frame::cosTheta(bRecInt.wo)))).exp();
if (measure == ESolidAngle)
result *= Frame::cosTheta(bRec.wo)
/ Frame::cosTheta(bRec2.wo);
result *= std::abs(Frame::cosTheta(bRec.wo)
/ Frame::cosTheta(bRecInt.wo));
return result;
}
@ -261,17 +256,13 @@ public:
}
Float pdf(const BSDFQueryRecord &bRec, EMeasure measure) const {
if (Frame::cosTheta(bRec.wi) <= 0 ||
Frame::cosTheta(bRec.wo) <= 0)
return 0.0f;
bool sampleSpecular = (bRec.typeMask & EDeltaReflection)
&& (bRec.component == -1 || bRec.component == (int) m_components.size()-1);
bool sampleNested = (bRec.typeMask & m_nested->getType() & BSDF::EAll)
&& (bRec.component == -1 || bRec.component < (int) m_components.size()-1);
Float R12;
Vector wiPrime = -refract(bRec.wi, R12);
Vector wiPrime = refractTo(EInterior, bRec.wi, R12);
/* Reallocate samples */
Float probSpecular = (R12*m_specularSamplingWeight) /
@ -283,18 +274,18 @@ public:
return sampleNested ? probSpecular : 1.0f;
} else if (sampleNested) {
Float R21;
BSDFQueryRecord bRec2(bRec);
bRec2.wi = wiPrime;
bRec2.wo = -refract(bRec.wo, R21);
BSDFQueryRecord bRecInt(bRec);
bRecInt.wi = wiPrime;
bRecInt.wo = refractTo(EInterior, bRec.wo, R21);
if (R12 == 1 || R21 == 1) /* Total internal reflection */
return 0.0f;
Float pdf = m_nested->pdf(bRec2, measure);
Float pdf = m_nested->pdf(bRecInt, measure);
if (measure == ESolidAngle)
pdf *= Frame::cosTheta(bRec.wo)
/ Frame::cosTheta(bRec2.wo);
pdf *= std::abs(Frame::cosTheta(bRec.wo)
/ Frame::cosTheta(bRecInt.wo));
Float eta = m_extIOR / m_intIOR;
pdf *= eta * eta;
@ -311,21 +302,11 @@ public:
bool sampleNested = (bRec.typeMask & m_nested->getType() & BSDF::EAll)
&& (bRec.component == -1 || bRec.component < (int) m_components.size()-1);
if ((!sampleSpecular && !sampleNested) || Frame::cosTheta(bRec.wi) <= 0)
if ((!sampleSpecular && !sampleNested))
return Spectrum(0.0f);
/* Refract the incident direction and compute the Fresnel reflectance */
Float eta = m_extIOR / m_intIOR,
sinThetaTSqr = eta*eta * Frame::sinTheta2(bRec.wi),
R12, cosThetaT = 0;
if (sinThetaTSqr >= 1.0f) {
R12 = 1.0f; /* Total internal reflection */
} else {
cosThetaT = -std::sqrt(1.0f - sinThetaTSqr);
R12 = fresnelDielectric(Frame::cosTheta(bRec.wi),
-cosThetaT, m_extIOR, m_intIOR);
}
Float R12;
Vector wiPrime = refractTo(EInterior, bRec.wi, R12);
/* Reallocate samples */
Float probSpecular = (R12*m_specularSamplingWeight) /
@ -353,27 +334,30 @@ public:
return Spectrum(0.0f);
Vector wiBackup = bRec.wi;
bRec.wi = -refract(bRec.wi, eta, cosThetaT);
bRec.wi = wiPrime;
Spectrum result = m_nested->sample(bRec, pdf, sample);
bRec.wi = wiBackup;
Vector woPrime = bRec.wo;
if (result.isZero())
return Spectrum(0.0f);
Spectrum sigmaA = m_sigmaA->getValue(bRec.its) * m_thickness;
if (!sigmaA.isZero())
result *= (-sigmaA *
(1/std::abs(Frame::cosTheta(bRec.wi)) +
1/std::abs(Frame::cosTheta(bRec.wo)))).exp();
(1/std::abs(Frame::cosTheta(wiPrime)) +
1/std::abs(Frame::cosTheta(woPrime)))).exp();
Float R21, cosThetaWoPrime = Frame::cosTheta(bRec.wo);
bRec.wo = refract(-bRec.wo, R21);
bRec.wi = wiBackup;
Float R21;
bRec.wo = refractTo(EExterior, woPrime, R21);
if (R21 == 1.0f) /* Total internal reflection */
return Spectrum(0.0f);
Float eta = m_extIOR / m_intIOR;
bool sampledSA = (BSDF::getMeasure(bRec.sampledType) == ESolidAngle);
Float cosRatio = Frame::cosTheta(bRec.wo) / cosThetaWoPrime,
commonTerms = (sampledSA ? cosRatio : 1.0f)* eta * eta;
Float cosRatio = std::abs(Frame::cosTheta(bRec.wo) / Frame::cosTheta(woPrime)),
commonTerms = (sampledSA ? cosRatio : 1.0f) * eta * eta;
pdf *= (sampleSpecular ? (1 - probSpecular) : 1.0f) * commonTerms;
result *= (1 - R12) * (1 - R21) * commonTerms;

2
src/libcore/util.cpp
View File

@ -667,7 +667,7 @@ Vector squareToCone(Float cosCutoff, const Point2 &sample) {
}
Point2 squareToStdNormal(const Point2 &sample) {
Float tmp1 = std::sqrt(-2 * std::log(sample.x)),
Float tmp1 = std::sqrt(-2 * std::log(1-sample.x)),
tmp2 = 2 * M_PI * sample.y;
return Point2(
tmp1 * std::cos(tmp2),