/*
    This file is part of Mitsuba, a physically based rendering system.

    Copyright (c) 2007-2014 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 <http://www.gnu.org/licenses/>.
*/

#include <mitsuba/render/bsdf.h>
#include <mitsuba/hw/basicshader.h>
#include "microfacet.h"
#include "rtrans.h"
#include "ior.h"

MTS_NAMESPACE_BEGIN

/*!\plugin{roughcoating}{Rough dielectric coating}
 * \order{11}
 * \icon{bsdf_roughcoating}
 * \parameters{
 *     \parameter{distribution}{\String}{
 *          Specifies the type of microfacet normal distribution
 *          used to model the surface roughness.
 *          \vspace{-1mm}
 *       \begin{enumerate}[(i)]
 *           \item \code{beckmann}: Physically-based distribution derived from
 *               Gaussian random surfaces. This is the default.\vspace{-1.5mm}
 *           \item \code{ggx}: The GGX \cite{Walter07Microfacet} distribution (also known as
 *               Trowbridge-Reitz \cite{Trowbridge19975Average} distribution)
 *               was designed to better approximate the long tails observed in measurements
 *               of ground surfaces, which are not modeled by the Beckmann distribution.
 *           \vspace{-1.5mm}
 *           \item \code{phong}: Classical Phong distribution.
 *              In most cases, the \code{ggx} and \code{beckmann} distributions
 *              should be preferred, since they provide better importance sampling
 *              and accurate shadowing/masking computations.
 *              \vspace{-4mm}
 *       \end{enumerate}
 *     }
 *     \parameter{alpha}{\Float\Or\Texture}{
 *         Specifies the roughness of the unresolved surface micro-geometry.
 *         When the Beckmann distribution is used, this parameter is equal to the
 *         \emph{root mean square} (RMS) slope of the microfacets.
 *         \default{0.1}.
 *     }
 *     \parameter{sampleVisible}{\Boolean}{
 *	       Enables an improved importance sampling technique. Refer to
 *	       pages \pageref{plg:roughconductor} and \pageref{sec:visiblenormal-sampling}
 *	       for details. \default{\code{true}}
 *     }
 *     \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 layer (to
 *      model absorption --- should be specified 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}}
 *     \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}}
 *     \parameter{\Unnamed}{\BSDF}{A nested BSDF model that should be coated.}
 * }
 * \renderings{
 *     \rendering{Rough gold coated with a \emph{smooth} varnish layer}
 *         {bsdf_roughcoating_gold_smooth}
 *     \rendering{Rough gold coated with a \emph{rough} ($\alpha\!=\!0.03$) varnish layer}
 *         {bsdf_roughcoating_gold_rough}
 * }
 *
 * This plugin implements a \emph{very} approximate\footnote{
 * The model only accounts for roughness
 * in the specular reflection and Fresnel transmittance through the interface.
 * The interior model receives incident illumination
 * that is transformed \emph{as if} the coating was smooth. While
 * that's not quite correct, it is a convenient workaround when the
 * \pluginref{coating} plugin produces specular highlights that are too sharp.}
 * model that simulates a rough dielectric coating. It is essentially the
 * roughened version of \pluginref{coating}.
 * Any BSDF in Mitsuba can be coated using this plugin and multiple coating
 * layers can even be applied in sequence, which allows designing interesting
 * custom materials. 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).
 *
 * The implementation here is motivated by the paper
 * ``Arbitrarily Layered Micro-Facet Surfaces'' by Weidlich and
 * Wilkie \cite{Weidlich2007Arbitrarily}, though the implementation
 * works differently.
 */
class RoughCoating : public BSDF {
public:
	/// \sa refractTo()
	enum EDestination {
		EInterior = 0,
		EExterior = 1
	};

	RoughCoating(const Properties &props) : BSDF(props) {
		/* Specifies the internal index of refraction at the interface */
		Float intIOR = lookupIOR(props, "intIOR", "bk7");

		/* Specifies the external index of refraction at the interface */
		Float extIOR = lookupIOR(props, "extIOR", "air");

		if (intIOR < 0 || extIOR < 0 || intIOR == extIOR)
			Log(EError, "The interior and exterior indices of "
				"refraction must be positive and differ!");

		m_eta = intIOR / extIOR;
		m_invEta = 1 / m_eta;

		/* Specifies the absorption within the layer */
		m_sigmaA = new ConstantSpectrumTexture(
			props.getSpectrum("sigmaA", Spectrum(0.0f)));

		/* Specifies the layer's thickness using the inverse units of sigmaA */
		m_thickness = props.getFloat("thickness", 1);

		/* Specifies a multiplier for the specular reflectance component */
		m_specularReflectance = new ConstantSpectrumTexture(
			props.getSpectrum("specularReflectance", Spectrum(1.0f)));

		MicrofacetDistribution distr(props);
		m_type = distr.getType();
		m_sampleVisible = distr.getSampleVisible();

		if (distr.isAnisotropic())
			Log(EError, "The 'roughplastic' plugin currently does not support "
				"anisotropic microfacet distributions!");

		m_alpha = new ConstantFloatTexture(distr.getAlpha());

		m_specularSamplingWeight = 0.0f;
	}

	RoughCoating(Stream *stream, InstanceManager *manager)
	 : BSDF(stream, manager) {
		m_type = (MicrofacetDistribution::EType) stream->readUInt();
		m_sampleVisible = stream->readBool();
		m_nested = static_cast<BSDF *>(manager->getInstance(stream));
		m_sigmaA = static_cast<Texture *>(manager->getInstance(stream));
		m_specularReflectance = static_cast<Texture *>(manager->getInstance(stream));
		m_alpha = static_cast<Texture *>(manager->getInstance(stream));
		m_eta = stream->readFloat();
		m_thickness = stream->readFloat();
		m_invEta = 1 / m_eta;

		configure();
	}

	void serialize(Stream *stream, InstanceManager *manager) const {
		BSDF::serialize(stream, manager);

		stream->writeUInt((uint32_t) m_type);
		stream->writeBool(m_sampleVisible);
		manager->serialize(stream, m_nested.get());
		manager->serialize(stream, m_sigmaA.get());
		manager->serialize(stream, m_specularReflectance.get());
		manager->serialize(stream, m_alpha.get());
		stream->writeFloat(m_eta);
		stream->writeFloat(m_thickness);
	}

	void configure() {
		unsigned int extraFlags = 0;
		if (!m_sigmaA->isConstant() || !m_alpha->isConstant())
			extraFlags |= ESpatiallyVarying;

		m_components.clear();
		for (int i=0; i<m_nested->getComponentCount(); ++i)
			m_components.push_back(m_nested->getType(i) | extraFlags);

		m_components.push_back(EGlossyReflection | EFrontSide | EBackSide
			| (m_specularReflectance->isConstant() ? 0 : ESpatiallyVarying));

		m_usesRayDifferentials = m_nested->usesRayDifferentials()
			|| m_sigmaA->usesRayDifferentials()
			|| m_alpha->usesRayDifferentials()
			|| m_specularReflectance->usesRayDifferentials();

		/* Compute weights that further steer samples towards
		   the specular or nested components */
		Float avgAbsorption = (m_sigmaA->getAverage()
			 *(-2*m_thickness)).exp().average();

		m_specularSamplingWeight = 1.0f / (avgAbsorption + 1.0f);

		/* Verify the input parameters and fix them if necessary */
		m_specularReflectance = ensureEnergyConservation(
			m_specularReflectance, "specularReflectance", 1.0f);

		if (!m_roughTransmittance.get()) {
			/* Load precomputed data used to compute the rough
			   transmittance through the dielectric interface */
			m_roughTransmittance = new RoughTransmittance(m_type);

			m_roughTransmittance->checkEta(m_eta);
			m_roughTransmittance->checkAlpha(m_alpha->getMinimum().average());
			m_roughTransmittance->checkAlpha(m_alpha->getMaximum().average());

			/* Reduce the rough transmittance data to a 2D slice */
			m_roughTransmittance->setEta(m_eta);

			/* If possible, even reduce it to a 1D slice */
			if (m_alpha->isConstant())
				m_roughTransmittance->setAlpha(
					m_alpha->eval(Intersection()).average());
		}

		BSDF::configure();
	}

	/// Helper function: reflect \c wi with respect to a given surface normal
	inline Vector reflect(const Vector &wi, const Normal &m) const {
		return 2 * dot(wi, m) * Vector(m) - wi;
	}

	/// Refraction in local coordinates
	Vector refractTo(EDestination dest, const Vector &wi) const {
		Float cosThetaI = Frame::cosTheta(wi);
		Float invEta = (dest == EInterior) ? m_invEta : m_eta;

		bool entering = cosThetaI > 0.0f;

		/* Using Snell's law, calculate the squared sine of the
		   angle between the normal and the transmitted ray */
		Float sinThetaTSqr = invEta*invEta * Frame::sinTheta2(wi);

		if (sinThetaTSqr >= 1.0f) {
			/* Total internal reflection */
			return Vector(0.0f);
		} else {
			Float cosThetaT = std::sqrt(1.0f - sinThetaTSqr);

			/* Retain the directionality of the vector */
			return Vector(invEta*wi.x, invEta*wi.y,
				entering ? cosThetaT : -cosThetaT);
		}
	}

	Spectrum eval(const BSDFSamplingRecord &bRec, EMeasure measure) const {
		bool hasNested = (bRec.typeMask & m_nested->getType() & BSDF::EAll)
			&& (bRec.component == -1 || bRec.component < (int) m_components.size()-1);
		bool hasSpecular = (bRec.typeMask & EGlossyReflection)
			&& (bRec.component == -1 || bRec.component == (int) m_components.size()-1)
			&& measure == ESolidAngle;

		/* Construct the microfacet distribution matching the
		   roughness values at the current surface position. */
		MicrofacetDistribution distr(
			m_type,
			m_alpha->eval(bRec.its).average(),
			m_sampleVisible
		);

		Spectrum result(0.0f);
		if (hasSpecular && Frame::cosTheta(bRec.wo) * Frame::cosTheta(bRec.wi) > 0) {
			/* Calculate the reflection half-vector */
			const Vector H = normalize(bRec.wo+bRec.wi)
				* math::signum(Frame::cosTheta(bRec.wo));

			/* Evaluate the microfacet normal distribution */
			const Float D = distr.eval(H);

			/* Fresnel term */
			const Float F = fresnelDielectricExt(absDot(bRec.wi, H), m_eta);

			/* Smith's shadow-masking function */
			const Float G = distr.G(bRec.wi, bRec.wo, H);

			/* Calculate the specular reflection component */
			Float value = F * D * G /
				(4.0f * std::abs(Frame::cosTheta(bRec.wi)));

			result += m_specularReflectance->eval(bRec.its) * value;
		}

		if (hasNested) {
			BSDFSamplingRecord bRecInt(bRec);
			bRecInt.wi = refractTo(EInterior, bRec.wi);
			bRecInt.wo = refractTo(EInterior, bRec.wo);

			Spectrum nestedResult = m_nested->eval(bRecInt, measure) *
				m_roughTransmittance->eval(std::abs(Frame::cosTheta(bRec.wi)), distr.getAlpha()) *
				m_roughTransmittance->eval(std::abs(Frame::cosTheta(bRec.wo)), distr.getAlpha());

			Spectrum sigmaA = m_sigmaA->eval(bRec.its) * m_thickness;
			if (!sigmaA.isZero())
				nestedResult *= (-sigmaA *
					(1/std::abs(Frame::cosTheta(bRecInt.wi)) +
					 1/std::abs(Frame::cosTheta(bRecInt.wo)))).exp();

			if (measure == ESolidAngle) {
				/* Solid angle compression & irradiance conversion factors */
				nestedResult *= m_invEta * m_invEta *
					  Frame::cosTheta(bRec.wi) * Frame::cosTheta(bRec.wo)
				   / (Frame::cosTheta(bRecInt.wi) * Frame::cosTheta(bRecInt.wo));
			}

			result += nestedResult;
		}

		return result;
	}

	Float pdf(const BSDFSamplingRecord &bRec, EMeasure measure) const {
		bool hasNested = (bRec.typeMask & m_nested->getType() & BSDF::EAll)
			&& (bRec.component == -1 || bRec.component < (int) m_components.size()-1);
		bool hasSpecular = (bRec.typeMask & EGlossyReflection)
			&& (bRec.component == -1 || bRec.component == (int) m_components.size()-1)
			&& measure == ESolidAngle;

		/* Calculate the reflection half-vector */
		const Vector H = normalize(bRec.wo+bRec.wi)
				* math::signum(Frame::cosTheta(bRec.wo));

		/* Construct the microfacet distribution matching the
		   roughness values at the current surface position. */
		MicrofacetDistribution distr(
			m_type,
			m_alpha->eval(bRec.its).average(),
			m_sampleVisible
		);

		Float probNested, probSpecular;
		if (hasSpecular && hasNested) {
			/* Find the probability of sampling the specular component */
			probSpecular = 1-m_roughTransmittance->eval(
				std::abs(Frame::cosTheta(bRec.wi)), distr.getAlpha());

			/* Reallocate samples */
			probSpecular = (probSpecular*m_specularSamplingWeight) /
				(probSpecular*m_specularSamplingWeight +
				(1-probSpecular) * (1-m_specularSamplingWeight));

			probNested = 1 - probSpecular;
		} else {
			probNested = probSpecular = 1.0f;
		}

		Float result = 0.0f;
		if (hasSpecular && Frame::cosTheta(bRec.wo) * Frame::cosTheta(bRec.wi) > 0) {
			/* Jacobian of the half-direction mapping */
			const Float dwh_dwo = 1.0f / (4.0f * absDot(bRec.wo, H));

			/* Evaluate the microfacet model sampling density function */
			const Float prob = distr.pdf(bRec.wi, H);

			result = prob * dwh_dwo * probSpecular;
		}

		if (hasNested) {
			BSDFSamplingRecord bRecInt(bRec);
			bRecInt.wi = refractTo(EInterior, bRec.wi);
			bRecInt.wo = refractTo(EInterior, bRec.wo);

			Float prob = m_nested->pdf(bRecInt, measure);

			if (measure == ESolidAngle) {
				prob *= m_invEta * m_invEta * Frame::cosTheta(bRec.wo)
			          / Frame::cosTheta(bRecInt.wo);
			}

			result += prob * probNested;
		}

		return result;
	}

	inline Spectrum sample(BSDFSamplingRecord &bRec, Float &_pdf, const Point2 &_sample) const {
		bool hasNested = (bRec.typeMask & m_nested->getType() & BSDF::EAll)
			&& (bRec.component == -1 || bRec.component < (int) m_components.size()-1);
		bool hasSpecular = (bRec.typeMask & EGlossyReflection)
			&& (bRec.component == -1 || bRec.component == (int) m_components.size()-1);

		bool choseSpecular = hasSpecular;
		Point2 sample(_sample);

		/* Construct the microfacet distribution matching the
		   roughness values at the current surface position. */
		MicrofacetDistribution distr(
			m_type,
			m_alpha->eval(bRec.its).average(),
			m_sampleVisible
		);

		Float probSpecular;
		if (hasSpecular && hasNested) {
			/* Find the probability of sampling the diffuse component */
			probSpecular = 1 - m_roughTransmittance->eval(
				std::abs(Frame::cosTheta(bRec.wi)), distr.getAlpha());

			/* Reallocate samples */
			probSpecular = (probSpecular*m_specularSamplingWeight) /
				(probSpecular*m_specularSamplingWeight +
				(1-probSpecular) * (1-m_specularSamplingWeight));

			if (sample.y < probSpecular) {
				sample.y /= probSpecular;
			} else {
				sample.y = (sample.y - probSpecular) / (1 - probSpecular);
				choseSpecular = false;
			}
		}

		if (choseSpecular) {
			/* Perfect specular reflection based on the microfacet normal */
			Normal m = distr.sample(bRec.wi, sample);
			bRec.wo = reflect(bRec.wi, m);
			bRec.sampledComponent = (int) m_components.size() - 1;
			bRec.sampledType = EGlossyReflection;
			bRec.eta = 1.0f;

			/* Side check */
			if (Frame::cosTheta(bRec.wo) * Frame::cosTheta(bRec.wi) <= 0)
				return Spectrum(0.0f);
		} else {
			Vector wiBackup = bRec.wi;
			bRec.wi = refractTo(EInterior, bRec.wi);
			Spectrum result = m_nested->sample(bRec, _pdf, sample);
			bRec.wi = wiBackup;
			if (result.isZero())
				return Spectrum(0.0f);
			bRec.wo = refractTo(EExterior, bRec.wo);
			if (bRec.wo.isZero())
				return Spectrum(0.0f);
		}

		/* Guard against numerical imprecisions */
		EMeasure measure = getMeasure(bRec.sampledType);
		_pdf = pdf(bRec, measure);

		if (_pdf == 0)
			return Spectrum(0.0f);
		else
			return eval(bRec, measure) / _pdf;
	}

	Spectrum sample(BSDFSamplingRecord &bRec, const Point2 &sample) const {
		Float pdf;
		return RoughCoating::sample(bRec, pdf, sample);
	}

	Float getRoughness(const Intersection &its, int component) const {
		return component < (int) m_components.size() - 1
			? m_nested->getRoughness(its, component)
			: m_alpha->eval(its).average();
	}

	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<BSDF *>(child);
		} else if (child->getClass()->derivesFrom(MTS_CLASS(Texture))) {
			if (name == "sigmaA")
				m_sigmaA = static_cast<Texture *>(child);
			else if (name == "alpha")
				m_alpha = static_cast<Texture *>(child);
			else
				BSDF::addChild(name, child);
		} else {
			BSDF::addChild(name, child);
		}
	}

	std::string toString() const {
		std::ostringstream oss;
		oss << "RoughCoating[" << endl
			<< "  id = \"" << getID() << "\"," << endl
			<< "  distribution = " << MicrofacetDistribution::distributionName(m_type) << "," << endl
			<< "  sampleVisible = " << m_sampleVisible << "," << endl
			<< "  alpha = " << indent(m_alpha->toString()) << "," << endl
			<< "  sigmaA = " << indent(m_sigmaA->toString()) << "," << endl
			<< "  specularReflectance = " << indent(m_specularReflectance->toString()) << "," << endl
			<< "  specularSamplingWeight = " << m_specularSamplingWeight << "," << endl
			<< "  diffuseSamplingWeight = " << (1-m_specularSamplingWeight) << "," << endl
			<< "  eta = " << m_eta << "," << endl
			<< "  nested = " << indent(m_nested.toString()) << endl
			<< "]";
		return oss.str();
	}

	Shader *createShader(Renderer *renderer) const;

	MTS_DECLARE_CLASS()
private:
	MicrofacetDistribution::EType m_type;
	ref<RoughTransmittance> m_roughTransmittance;
	ref<Texture> m_sigmaA;
	ref<Texture> m_alpha;
	ref<Texture> m_specularReflectance;
	ref<BSDF> m_nested;
	Float m_eta, m_invEta;
	Float m_specularSamplingWeight;
	Float m_thickness;
	bool m_sampleVisible;
};

/**
 * GLSL port of the rough coating shader. This version is much more
 * approximate -- it only supports the Beckmann distribution,
 * does everything in RGB, uses a cheaper shadowing-masking term, and
 * it also makes use of the Schlick approximation to the Fresnel
 * reflectance of dielectrics. When the roughness is lower than
 * \alpha < 0.2, the shader clamps it to 0.2 so that it will still perform
 * reasonably well in a VPL-based preview.
 */
class RoughCoatingShader : public Shader {
public:
	RoughCoatingShader(Renderer *renderer, const BSDF *nested,
				const Texture *sigmaA, const Texture *alpha,
				Float eta) : Shader(renderer, EBSDFShader),
			m_nested(nested), m_sigmaA(sigmaA), m_alpha(alpha), m_eta(eta) {
		m_nestedShader = renderer->registerShaderForResource(m_nested.get());
		m_sigmaAShader = renderer->registerShaderForResource(m_sigmaA.get());
		m_alphaShader = renderer->registerShaderForResource(m_alpha.get());
		m_R0 = fresnelDielectricExt(1.0f, eta);
	}

	bool isComplete() const {
		return m_nestedShader.get() != NULL
			&& m_sigmaAShader.get() != NULL
			&& m_alphaShader.get() != NULL;
	}

	void putDependencies(std::vector<Shader *> &deps) {
		deps.push_back(m_nestedShader.get());
		deps.push_back(m_sigmaAShader.get());
		deps.push_back(m_alphaShader.get());
	}

	void cleanup(Renderer *renderer) {
		renderer->unregisterShaderForResource(m_nested.get());
		renderer->unregisterShaderForResource(m_sigmaA.get());
		renderer->unregisterShaderForResource(m_alpha.get());
	}

	void resolve(const GPUProgram *program, const std::string &evalName, std::vector<int> &parameterIDs) const {
		parameterIDs.push_back(program->getParameterID(evalName + "_R0", false));
		parameterIDs.push_back(program->getParameterID(evalName + "_eta", false));
	}

	void bind(GPUProgram *program, const std::vector<int> &parameterIDs, int &textureUnitOffset) const {
		program->setParameter(parameterIDs[0], m_R0);
		program->setParameter(parameterIDs[1], m_eta);
	}

	void generateCode(std::ostringstream &oss,
			const std::string &evalName,
			const std::vector<std::string> &depNames) const {
		oss << "uniform float " << evalName << "_R0;" << endl
			<< "uniform float " << evalName << "_eta;" << endl
			<< endl
			<< "float " << evalName << "_schlick(float ct) {" << endl
			<< "    float ctSqr = ct*ct, ct5 = ctSqr*ctSqr*ct;" << endl
			<< "    return " << evalName << "_R0 + (1.0 - " << evalName << "_R0) * ct5;" << endl
			<< "}" << endl
			<< endl
			<< "vec3 " << evalName << "_refract(vec3 wi, out float T) {" << endl
			<< "    float cosThetaI = cosTheta(wi);" << endl
			<< "    bool entering = cosThetaI > 0.0;" << endl
			<< "    float invEta = 1.0 / " << evalName << "_eta;" << endl
			<< "    float sinThetaTSqr =  invEta * invEta * sinTheta2(wi);" << endl
			<< "    if (sinThetaTSqr >= 1.0) {" << endl
			<< "        T = 0.0; /* Total internal reflection */" << endl
			<< "        return vec3(0.0);" << endl
			<< "    } else {" << endl
			<< "        float cosThetaT = sqrt(1.0 - sinThetaTSqr);" << endl
			<< "        T = 1.0 - " << evalName << "_schlick(1.0 - abs(cosThetaI));" << endl
			<< "        return vec3(invEta*wi.x, invEta*wi.y, entering ? cosThetaT : -cosThetaT);" << endl
			<< "    }" << endl
			<< "}" << endl
			<< endl
			<< "float " << evalName << "_D(vec3 m, float alpha) {" << endl
			<< "    float ct = cosTheta(m);" << endl
			<< "    if (cosTheta(m) <= 0.0)" << endl
			<< "        return 0.0;" << endl
			<< "    float ex = tanTheta(m) / alpha;" << endl
			<< "    return exp(-(ex*ex)) / (pi * alpha * alpha *" << endl
			<< "               pow(cosTheta(m), 4.0));" << endl
			<< "}" << endl
			<< endl
			<< "float " << evalName << "_G(vec3 m, vec3 wi, vec3 wo) {" << endl
			<< "    if ((dot(wi, m) * cosTheta(wi)) <= 0 || " << endl
			<< "        (dot(wo, m) * cosTheta(wo)) <= 0)" << endl
			<< "        return 0.0;" << endl
			<< "    float nDotM = cosTheta(m);" << endl
			<< "    return min(1.0, min(" << endl
			<< "        abs(2 * nDotM * cosTheta(wo) / dot(wo, m))," << endl
			<< "        abs(2 * nDotM * cosTheta(wi) / dot(wi, m))));" << endl
			<< "}" << endl
			<< endl
			<< "vec3 " << evalName << "(vec2 uv, vec3 wi, vec3 wo) {" << endl
			<< "    float T12, T21;" << endl
			<< "    vec3 wiPrime = " << evalName << "_refract(wi, T12);" << endl
			<< "    vec3 woPrime = " << evalName << "_refract(wo, T21);" << endl
			<< "    vec3 nested = " << depNames[0] << "(uv, wiPrime, woPrime);" << endl
			<< "    vec3 sigmaA = " << depNames[1] << "(uv);" << endl
			<< "    vec3 result = nested * " << evalName << "_eta * " << evalName << "_eta" << endl
			<< "                  * T12 * T21 * (cosTheta(wi)*cosTheta(wo)) /" << endl
			<< "                  (cosTheta(wiPrime)*cosTheta(woPrime));" << endl
			<< "    if (sigmaA != vec3(0.0))" << endl
			<< "        result *= exp(-sigmaA * (1/abs(cosTheta(wiPrime)) + " << endl
			<< "                                 1/abs(cosTheta(woPrime))));" << endl
			<< "    if (cosTheta(wi)*cosTheta(wo) > 0) {" << endl
			<< "        vec3 H = normalize(wi + wo);" << endl
			<< "        float alpha = max(0.2, " << depNames[2] << "(uv)[0]);" << endl
			<< "        float D = " << evalName << "_D(H, alpha)" << ";" << endl
			<< "        float G = " << evalName << "_G(H, wi, wo);" << endl
			<< "        float F = " << evalName << "_schlick(1-dot(wi, H));" << endl
			<< "        result += vec3(F * D * G / (4*cosTheta(wi)));" << endl
			<< "    }" << endl
			<< "    return result;" << endl
			<< "}" << endl
			<< endl
			<< "vec3 " << evalName << "_diffuse(vec2 uv, vec3 wi, vec3 wo) {" << endl
			<< "    return " << depNames[0] << "_diffuse(uv, wi, wo);" << endl
			<< "}" << endl;
	}

	MTS_DECLARE_CLASS()
private:
	ref<const BSDF> m_nested;
	ref<Shader> m_nestedShader;
	ref<const Texture> m_sigmaA;
	ref<Shader> m_sigmaAShader;
	ref<const Texture> m_alpha;
	ref<Shader> m_alphaShader;
	Float m_R0, m_eta;
};

Shader *RoughCoating::createShader(Renderer *renderer) const {
	return new RoughCoatingShader(renderer, m_nested.get(),
		m_sigmaA.get(), m_alpha.get(), m_eta);
}

MTS_IMPLEMENT_CLASS(RoughCoatingShader, false, Shader)
MTS_IMPLEMENT_CLASS_S(RoughCoating, false, BSDF)
MTS_EXPORT_PLUGIN(RoughCoating, "Rough coating BSDF");
MTS_NAMESPACE_END