/* This file is part of Mitsuba, a physically based rendering system. Copyright (c) 2007-2011 by Wenzel Jakob and others. Mitsuba is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License Version 3 as published by the Free Software Foundation. Mitsuba is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . */ #include #include #include "ior.h" MTS_NAMESPACE_BEGIN /*! \plugin{coating}{Smooth dielectric coating} * \order{9} * * \parameters{ * \parameter{intIOR}{\Float\Or\String}{Interior index of refraction specified * numerically or using a known material name. \default{\texttt{bk7} / 1.5046}} * \parameter{extIOR}{\Float\Or\String}{Exterior index of refraction specified * numerically or using a known material name. \default{\texttt{air} / 1.000277}} * \parameter{thickness}{\Float}{Denotes the thickness of the absorbing layer (given in inverse units of \code{sigmaA})\default{1}} * \parameter{sigmaA}{\Spectrum\Or\Texture}{The absorption coefficient of the coating layer. \default{0, i.e. there is no absorption}} * } * * \renderings{ * \rendering{Rough copper} * {bsdf_roughconductor_copper} * \rendering{The same material coated with a single layer of clear varnish (see \lstref{coating-roughcopper})} * {bsdf_coating_roughconductor} * } * * This plugin implements a smooth dielectric coating (e.g. a layer of varnish) * in the style of the paper ``Arbitrarily Layered Micro-Facet Surfaces'' by * Weidlich and Wilkie \cite{Weidlich2007Arbitrarily}. Any non-transmissive * BSDF in Mitsuba can be coated using this plugin, and multiple coating layers * can be applied in sequence. This allows designing interesting custom materials * like car paint or glazed metal foil. The coating layer can optionally be * tinted (i.e. filled with an absorbing medium), in which case this model also * accounts for the directionally dependent absorption within the layer. * * Note that the plugin discards illumination that undergoes internal * reflection within the coating. This can lead to a noticeable energy * loss for materials that reflect much of their energy near or below the critical * angle (i.e. diffuse or very rough materials). * Therefore, users are discouraged to use this plugin to coat smooth * diffuse materials, since there is a separately available plugin * named \pluginref{smoothplastic}, which covers the same case and does not * suffer from energy loss. * * Evaluating the internal component of this model entails refracting the * incident and exitant rays through the dielectric interface, followed by * querying the nested material with this modified direction pair. The result * is attenuated by the two Fresnel transmittances and the absorption, if any. * * \vspace{4mm} * * \begin{xml}[caption=Rough copper coated with a transparent layer of * varnish, label=lst:coating-roughcopper] * * * * * * * * \end{xml} */ class SmoothCoating : public BSDF { public: SmoothCoating(const Properties &props) : BSDF(props) { /* Specifies the internal index of refraction at the interface */ m_intIOR = lookupIOR(props, "intIOR", "bk7"); /* Specifies the external index of refraction at the interface */ m_extIOR = lookupIOR(props, "extIOR", "air"); /* Specifies the layer's thickness using the inverse units of sigmaA */ m_thickness = props.getFloat("thickness", 1); /* Specifies the absorption within the layer */ m_sigmaA = new ConstantSpectrumTexture( props.getSpectrum("sigmaA", Spectrum(0.0f))); } SmoothCoating(Stream *stream, InstanceManager *manager) : BSDF(stream, manager) { m_intIOR = stream->readFloat(); m_extIOR = stream->readFloat(); m_thickness = stream->readFloat(); m_nested = static_cast(manager->getInstance(stream)); m_sigmaA = static_cast(manager->getInstance(stream)); configure(); } 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!"); #if COMPENSATE if (m_nested->getClass()->getName() == "SmoothDiffuse") { /* For an ideally diffuse material, it is known how much energy will be lost to total internal reflection */ m_compensation = (m_intIOR*m_intIOR) / (m_extIOR * m_extIOR); } else { /* Otherwise, give up (for now) */ m_compensation = 1.0f; } #endif unsigned int extraFlags = 0; if (!m_sigmaA->isConstant()) extraFlags |= ESpatiallyVarying; m_components.clear(); for (int i=0; igetComponentCount(); ++i) m_components.push_back(m_nested->getType(i) | extraFlags); m_components.push_back(EDeltaReflection | EFrontSide); m_usesRayDifferentials = m_nested->usesRayDifferentials() || m_sigmaA->usesRayDifferentials(); BSDF::configure(); } void serialize(Stream *stream, InstanceManager *manager) const { BSDF::serialize(stream, manager); stream->writeFloat(m_intIOR); stream->writeFloat(m_extIOR); stream->writeFloat(m_thickness); manager->serialize(stream, m_nested.get()); manager->serialize(stream, m_sigmaA.get()); } void addChild(const std::string &name, ConfigurableObject *child) { if (child->getClass()->derivesFrom(MTS_CLASS(BSDF))) { if (m_nested != NULL) Log(EError, "Only a single nested BRDF can be added!"); m_nested = static_cast(child); } else { BSDF::addChild(name, child); } } /// Reflection in local coordinates inline Vector reflect(const Vector &wi) const { 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; 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, sinThetaTSqr = eta*eta * Frame::sinTheta2(wi); if (sinThetaTSqr >= 1.0f) { /* Total internal reflection */ F = 1.0f; return Vector(0.0f); } else { Float cosThetaT = std::sqrt(1.0f - sinThetaTSqr); /* Compute the Fresnel transmittance */ F = fresnelDielectric(std::abs(Frame::cosTheta(wi)), cosThetaT, m_extIOR, m_intIOR); 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) && (bRec.component == -1 || bRec.component < (int) m_components.size()-1); 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)); } else if (sampleNested) { Float R12, R21; BSDFQueryRecord bRec2(bRec); bRec2.wi = -refract(bRec.wi, R12); bRec2.wo = -refract(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) * ((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(); if (measure == ESolidAngle) result *= Frame::cosTheta(bRec.wo) / Frame::cosTheta(bRec2.wo); #ifdef COMPENSATE result *= m_compensation; #endif return result; } return Spectrum(0.0f); } 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); if (measure == EDiscrete && sampleSpecular && std::abs(1-dot(reflect(bRec.wi), bRec.wo)) < Epsilon) { return sampleNested ? fresnel( Frame::cosTheta(bRec.wi), m_extIOR, m_intIOR) : 1.0f; } else if (sampleNested) { Float R12, R21; BSDFQueryRecord bRec2(bRec); bRec2.wi = -refract(bRec.wi, R12); bRec2.wo = -refract(bRec.wo, R21); if (R12 == 1 || R21 == 1) /* Total internal reflection */ return 0.0f; Float pdf = m_nested->pdf(bRec2, measure); if (measure == ESolidAngle) pdf *= Frame::cosTheta(bRec.wo) / Frame::cosTheta(bRec2.wo); Float eta = m_extIOR / m_intIOR; pdf *= eta * eta; return sampleSpecular ? (pdf * (1-R12)) : pdf; } else { return 0.0f; } } Spectrum sample(BSDFQueryRecord &bRec, Float &pdf, const Point2 &_sample) const { 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); if ((!sampleSpecular && !sampleNested) || Frame::cosTheta(bRec.wi) <= 0) 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); } bool choseSpecular = sampleSpecular; Point2 sample(_sample); if (sampleSpecular && sampleNested) { if (sample.x > R12) { sample.x = (sample.x - R12) / (1 - R12); choseSpecular = false; } } if (choseSpecular) { bRec.sampledComponent = m_components.size()-1; bRec.sampledType = EDeltaReflection; bRec.wo = reflect(bRec.wi); pdf = sampleNested ? R12 : 1.0f; return Spectrum(R12); } else { if (R12 == 1.0f) /* Total internal reflection */ return Spectrum(0.0f); Vector wiBackup = bRec.wi; bRec.wi = -refract(bRec.wi, eta, cosThetaT); Spectrum result = m_nested->sample(bRec, pdf, sample); 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(); Float R21, cosThetaWoPrime = Frame::cosTheta(bRec.wo); bRec.wo = refract(-bRec.wo, R21); bRec.wi = wiBackup; if (R21 == 1.0f) /* Total internal reflection */ return Spectrum(0.0f); bool sampledSA = (BSDF::getMeasure(bRec.sampledType) == ESolidAngle); Float cosRatio = Frame::cosTheta(bRec.wo) / cosThetaWoPrime, commonTerms = (sampledSA ? cosRatio : 1.0f)* eta * eta; pdf *= (sampleSpecular ? (1 - R12) : 1.0f) * commonTerms; result *= (1 - R12) * (1 - R21) * commonTerms; #ifdef COMPENSATE result *= m_compensation; #endif return result; } } Spectrum sample(BSDFQueryRecord &bRec, const Point2 &sample) const { Float pdf; Spectrum result = SmoothCoating::sample(bRec, pdf, sample); if (result.isZero()) return Spectrum(0.0f); else return result / pdf; } std::string toString() const { std::ostringstream oss; oss << "SmoothCoating[" << endl << " name = \"" << getName() << "\"," << endl << " intIOR = " << m_intIOR << "," << endl << " extIOR = " << m_extIOR << "," << endl << " sigmaA = " << indent(m_sigmaA->toString()) << "," << endl << " thickness = " << m_thickness << "," << endl << " nested = " << indent(m_nested->toString()) << endl << "]"; return oss.str(); } MTS_DECLARE_CLASS() protected: Float m_intIOR, m_extIOR; ref m_sigmaA; ref m_nested; Float m_thickness; #ifdef COMPENSATE Float m_compensation; #endif }; MTS_IMPLEMENT_CLASS_S(SmoothCoating, false, BSDF) MTS_EXPORT_PLUGIN(SmoothCoating, "Smooth dielectric coating"); MTS_NAMESPACE_END