/*
    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 <http://www.gnu.org/licenses/>.
*/

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

MTS_NAMESPACE_BEGIN

/*!\plugin{plastic}{Smooth plastic material}
 * \order{7}
 * \icon{bsdf_plastic}
 * \parameters{
 *     \parameter{intIOR}{\Float\Or\String}{Interior index of refraction specified
 *      numerically or using a known material name. \default{\texttt{polypropylene} / 1.49}}
 *     \parameter{extIOR}{\Float\Or\String}{Exterior index of refraction specified
 *      numerically or using a known material name. \default{\texttt{air} / 1.000277}}
 *     \parameter{specular\showbreak Reflectance}{\Spectrum\Or\Texture}{Optional
 *         factor used to modulate the specular reflection component. Note that for physical 
 *         realism, this parameter should never be touched. \default{1.0}}
 *     \parameter{diffuse\showbreak Reflectance}{\Spectrum\Or\Texture}{Optional
 *         factor used to modulate the diffuse reflection component\default{0.5}}
 * }
 *
 * \renderings{
 *     \rendering{A rendering with the default parameters}{bsdf_plastic_default}
 *     \rendering{A rendering with custom parameters (\lstref{plastic-shiny})}
 *         {bsdf_plastic_shiny}
 * }
 *
 * This plugin describes a perfectly smooth plastic-like dielectric material
 * with internal scattering. The model interpolates between ideally specular 
 * and ideally diffuse reflection based on the Fresnel reflectance (i.e. it 
 * does so in a way that depends on the angle of incidence). Similar to the 
 * \pluginref{dielectric} plugin, IOR values can either be specified 
 * numerically, or based on a list of known materials (see 
 * \tblref{dielectric-iors} for an overview). 
 *
 * Since it is very simple and fast, this model is often a better choice
 * than the \pluginref{phong}, \pluginref{ward}, and \pluginref{roughplastic}
 * plugins when rendering very smooth plastic-like materials. \vspace{4mm}
 *
 * \begin{xml}[caption=A shiny material whose diffuse reflectance is 
 *     specified using sRGB, label=lst:plastic-shiny]
 * <bsdf type="plastic">
 *     <srgb name="diffuseReflectance" value="#18455c"/>
 *     <float name="intIOR" value="1.9"/>
 * </bsdf>
 * \end{xml}
 */
class SmoothPlastic : public BSDF {
public:
	SmoothPlastic(const Properties &props) : BSDF(props) {
		/* Specifies the internal index of refraction at the interface */
		m_intIOR = lookupIOR(props, "intIOR", "polypropylene");

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

		m_specularReflectance = new ConstantSpectrumTexture(
			props.getSpectrum("specularReflectance", Spectrum(1.0f)));
		m_diffuseReflectance = new ConstantSpectrumTexture(
			props.getSpectrum("diffuseReflectance", Spectrum(0.5f)));
		m_specularSamplingWeight = 0.0f;
	}

	SmoothPlastic(Stream *stream, InstanceManager *manager) 
			: BSDF(stream, manager) {
		m_intIOR = stream->readFloat();
		m_extIOR = stream->readFloat();
		m_specularReflectance = static_cast<Texture *>(manager->getInstance(stream));
		m_diffuseReflectance = static_cast<Texture *>(manager->getInstance(stream));
		configure();
	}

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

		/* Compute weights that further steer samples towards
		   the specular or diffuse components */
		Float dAvg = m_diffuseReflectance->getAverage().getLuminance(),
			  sAvg = m_specularReflectance->getAverage().getLuminance();
		m_specularSamplingWeight = sAvg / (dAvg + sAvg);

		m_usesRayDifferentials = 
			m_specularReflectance->usesRayDifferentials() ||
			m_diffuseReflectance->usesRayDifferentials();
		
		m_components.clear();
		m_components.push_back(EDeltaReflection | EFrontSide
			| (m_specularReflectance->isConstant() ? 0 : ESpatiallyVarying));
		m_components.push_back(EDiffuseReflection | EFrontSide
			| (m_diffuseReflectance->isConstant() ? 0 : ESpatiallyVarying));
		
		BSDF::configure();
	}


	Spectrum getDiffuseReflectance(const Intersection &its) const {
		return m_diffuseReflectance->getValue(its);
	}

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

		stream->writeFloat(m_intIOR);
		stream->writeFloat(m_extIOR);
		manager->serialize(stream, m_specularReflectance.get());
		manager->serialize(stream, m_diffuseReflectance.get());
	}

	void addChild(const std::string &name, ConfigurableObject *child) {
		if (child->getClass()->derivesFrom(MTS_CLASS(Texture))) {
			if (name == "specularReflectance") 
				m_specularReflectance = static_cast<Texture *>(child);
			else if (name == "diffuseReflectance")
				m_diffuseReflectance = static_cast<Texture *>(child);
			else 
				BSDF::addChild(name, 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);
	}

	Spectrum eval(const BSDFQueryRecord &bRec, EMeasure measure) const {
		bool hasSpecular   = (bRec.typeMask & EDeltaReflection)
				&& (bRec.component == -1 || bRec.component == 0);
		bool hasDiffuse = (bRec.typeMask & EDiffuseReflection)
				&& (bRec.component == -1 || bRec.component == 1);

		if (Frame::cosTheta(bRec.wo) <= 0 || Frame::cosTheta(bRec.wi) <= 0)
			return Spectrum(0.0f);
				  
		Float Fr = fresnel(Frame::cosTheta(bRec.wi), m_extIOR, m_intIOR);

		if (measure == EDiscrete && hasSpecular) {
			/* Check if the provided direction pair matches an ideal
			   specular reflection; tolerate some roundoff errors */
			bool reflection = std::abs(1 - dot(reflect(bRec.wi), bRec.wo)) < Epsilon;
			if (reflection)
				return m_specularReflectance->getValue(bRec.its) * Fr;
		} else if (measure == ESolidAngle && hasDiffuse) {
			if (hasDiffuse)
				return m_diffuseReflectance->getValue(bRec.its) 
					* (INV_PI * Frame::cosTheta(bRec.wo) * (1-Fr));
		}

		return Spectrum(0.0f);
	}

	Float pdf(const BSDFQueryRecord &bRec, EMeasure measure) const {
		bool hasSpecular   = (bRec.typeMask & EDeltaReflection)
				&& (bRec.component == -1 || bRec.component == 0);
		bool hasDiffuse = (bRec.typeMask & EDiffuseReflection)
				&& (bRec.component == -1 || bRec.component == 1);

		if (Frame::cosTheta(bRec.wo) <= 0 || Frame::cosTheta(bRec.wi) <= 0)
			return 0.0f;

		Float probSpecular = 1.0f;
		if (hasSpecular && hasDiffuse) {
			Float Fr = fresnel(Frame::cosTheta(bRec.wi), m_extIOR, m_intIOR);
			probSpecular = (Fr*m_specularSamplingWeight) /
				(Fr*m_specularSamplingWeight + 
				(1-Fr) * (1-m_specularSamplingWeight));
		}

		if (measure == EDiscrete && hasSpecular) {
			/* Check if the provided direction pair matches an ideal
			   specular reflection; tolerate some roundoff errors */
			if (std::abs(1 - dot(reflect(bRec.wi), bRec.wo)) < Epsilon)
				return probSpecular;
		} else if (measure == ESolidAngle && hasDiffuse) {
			return Frame::cosTheta(bRec.wo) * INV_PI *
				(hasSpecular ? (1 - probSpecular) : 1.0f);
		}

		return 0.0f;
	}

	Spectrum sample(BSDFQueryRecord &bRec, const Point2 &sample) const {
		bool hasSpecular   = (bRec.typeMask & EDeltaReflection)
				&& (bRec.component == -1 || bRec.component == 0);
		bool hasDiffuse = (bRec.typeMask & EDiffuseReflection)
				&& (bRec.component == -1 || bRec.component == 1);
		
		if ((!hasDiffuse && !hasSpecular) || Frame::cosTheta(bRec.wi) <= 0)
			return Spectrum(0.0f);

		Float Fr = fresnel(Frame::cosTheta(bRec.wi), m_extIOR, m_intIOR);
		Float probSpecular = (Fr*m_specularSamplingWeight) /
			(Fr*m_specularSamplingWeight + 
			(1-Fr) * (1-m_specularSamplingWeight));

		if (hasDiffuse && hasSpecular) {
			/* Importance sample wrt. the Fresnel reflectance */
			if (sample.x <= probSpecular) {
				bRec.sampledComponent = 0;
				bRec.sampledType = EDeltaReflection;
				bRec.wo = reflect(bRec.wi);

				return m_specularReflectance->getValue(bRec.its) *
					(Fr / probSpecular);
			} else {
				bRec.sampledComponent = 1;
				bRec.sampledType = EDiffuseReflection;
				bRec.wo = squareToHemispherePSA(Point2(
					(sample.x - probSpecular) / (1 - probSpecular),
					sample.y
				));

				return m_diffuseReflectance->getValue(bRec.its) *
					((1-Fr) / (1-probSpecular));
			}
		} else if (hasSpecular) {
			bRec.sampledComponent = 0;
			bRec.sampledType = EDeltaReflection;
			bRec.wo = reflect(bRec.wi);
			return m_specularReflectance->getValue(bRec.its) * Fr;
		} else {
			bRec.sampledComponent = 1;
			bRec.sampledType = EDiffuseReflection;

			if (Fr == 1.0f) /* Total internal reflection */
				return Spectrum(0.0f);
				
			bRec.wo = squareToHemispherePSA(sample);

			return m_diffuseReflectance->getValue(bRec.its) * (1-Fr);
		}
	}

	Spectrum sample(BSDFQueryRecord &bRec, Float &pdf, const Point2 &sample) const {
		bool hasSpecular   = (bRec.typeMask & EDeltaReflection)
				&& (bRec.component == -1 || bRec.component == 0);
		bool hasDiffuse = (bRec.typeMask & EDiffuseReflection)
				&& (bRec.component == -1 || bRec.component == 1);
		
		if ((!hasDiffuse && !hasSpecular) || Frame::cosTheta(bRec.wi) <= 0)
			return Spectrum(0.0f);

		Float Fr = fresnel(Frame::cosTheta(bRec.wi), m_extIOR, m_intIOR);
		Float probSpecular = (Fr*m_specularSamplingWeight) /
			(Fr*m_specularSamplingWeight + 
			(1-Fr) * (1-m_specularSamplingWeight));

		if (hasDiffuse && hasSpecular) {
			/* Importance sample wrt. the Fresnel reflectance */
			if (sample.x <= probSpecular) {
				bRec.sampledComponent = 0;
				bRec.sampledType = EDeltaReflection;
				bRec.wo = reflect(bRec.wi);

				pdf = probSpecular;
				return m_specularReflectance->getValue(bRec.its)
					* Fr / probSpecular;
			} else {
				bRec.sampledComponent = 1;
				bRec.sampledType = EDiffuseReflection;
				bRec.wo = squareToHemispherePSA(Point2(
					(sample.x - probSpecular) / (1 - probSpecular),
					sample.y
				));
				pdf = (1-probSpecular) * Frame::cosTheta(bRec.wo) * INV_PI;
	
				return m_diffuseReflectance->getValue(bRec.its) 
					* (1-Fr) / (1-probSpecular);
			}
		} else if (hasSpecular) {
			bRec.sampledComponent = 0;
			bRec.sampledType = EDeltaReflection;
			bRec.wo = reflect(bRec.wi);
			pdf = 1;
			return m_specularReflectance->getValue(bRec.its) * Fr;
		} else {
			bRec.sampledComponent = 1;
			bRec.sampledType = EDiffuseReflection;

			if (Fr == 1.0f) /* Total internal reflection */
				return Spectrum(0.0f);
				
			bRec.wo = squareToHemispherePSA(sample);

			pdf = Frame::cosTheta(bRec.wo) * INV_PI;

			return m_diffuseReflectance->getValue(bRec.its) * (1-Fr);
		}
	}

	Shader *createShader(Renderer *renderer) const;

	std::string toString() const {
		std::ostringstream oss;
		oss << "SmoothPlastic[" << endl
			<< "  name = \"" << getName() << "\"," << endl
			<< "  specularReflectance = " << indent(m_specularReflectance->toString()) << "," << endl
			<< "  diffuseReflectance = " << indent(m_diffuseReflectance->toString()) << "," << endl
			<< "  specularSamplingWeight = " << m_specularSamplingWeight << "," << endl
			<< "  diffuseSamplingWeight = " << (1-m_specularSamplingWeight) << "," << endl
			<< "  intIOR = " << m_intIOR << "," << endl 
			<< "  extIOR = " << m_extIOR << endl
			<< "]";
		return oss.str();
	}

	MTS_DECLARE_CLASS()
private:
	Float m_intIOR, m_extIOR;
	ref<Texture> m_diffuseReflectance;
	ref<Texture> m_specularReflectance;
	Float m_specularSamplingWeight;
};

/**
 * Smooth plastic shader -- it is really hopeless to visualize
 * this material in the VPL renderer, so let's try to do at least 
 * something that suggests the presence of a specularly-reflecting
 * dielectric coating.
 */
class SmoothPlasticShader : public Shader {
public:
	SmoothPlasticShader(Renderer *renderer, const Texture *specularReflectance,
			const Texture *diffuseReflectance, Float extIOR, 
			Float intIOR) : Shader(renderer, EBSDFShader), 
			m_specularReflectance(specularReflectance), 
			m_diffuseReflectance(diffuseReflectance), 
			m_extIOR(extIOR), m_intIOR(intIOR) {
		m_specularReflectanceShader = renderer->registerShaderForResource(m_specularReflectance.get());
		m_diffuseReflectanceShader = renderer->registerShaderForResource(m_diffuseReflectance.get());
		m_alpha = 0.4f;
		m_R0 = fresnel(1.0f, m_extIOR, m_intIOR);
	}

	bool isComplete() const {
		return m_specularReflectanceShader.get() != NULL &&
			m_diffuseReflectanceShader.get() != NULL;
	}

	void putDependencies(std::vector<Shader *> &deps) {
		deps.push_back(m_specularReflectanceShader.get());
		deps.push_back(m_diffuseReflectanceShader.get());
	}

	void cleanup(Renderer *renderer) {
		renderer->unregisterShaderForResource(m_specularReflectance.get());
		renderer->unregisterShaderForResource(m_diffuseReflectance.get());
	}

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

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

	void generateCode(std::ostringstream &oss,
			const std::string &evalName,
			const std::vector<std::string> &depNames) const {
		oss << "uniform float " << evalName << "_alpha;" << endl
			<< "uniform float " << evalName << "_R0;" << endl
			<< endl
			<< "float " << evalName << "_D(vec3 m) {" << endl
			<< "    float ct = cosTheta(m);" << endl
			<< "    if (cosTheta(m) <= 0.0)" << endl
			<< "        return 0.0;" << endl
			<< "    float ex = tanTheta(m) / " << evalName << "_alpha;" << endl
			<< "    return exp(-(ex*ex)) / (pi * " << evalName << "_alpha" << endl
			<< "        * " << evalName << "_alpha * 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
			<< "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 << "(vec2 uv, vec3 wi, vec3 wo) {" << endl
			<< "    if (cosTheta(wi) <= 0 || cosTheta(wo) <= 0)" << endl
			<< "        return vec3(0.0);" << endl
			<< "    vec3 H = normalize(wi + wo);" << endl
			<< "    vec3 specRef = " << depNames[0] << "(uv);" << endl
			<< "    vec3 diffuseRef = " << depNames[1] << "(uv);" << endl
			<< "    float D = " << evalName << "_D(H)" << ";" << endl
			<< "    float G = " << evalName << "_G(H, wi, wo);" << endl
			<< "    float F = " << evalName << "_schlick(1-dot(wi, H));" << endl
			<< "    return specRef    * (F * D * G / (4*cosTheta(wi))) + " << endl
			<< "           diffuseRef * ((1-F) * cosTheta(wo) * 0.31831);" << endl
			<< "}" << endl
			<< endl
			<< "vec3 " << evalName << "_diffuse(vec2 uv, vec3 wi, vec3 wo) {" << endl
			<< "    vec3 diffuseRef = " << depNames[1] << "(uv);" << endl
			<< "    return diffuseRef * 0.31831 * cosTheta(wo);"<< endl
			<< "}" << endl;
	}
	MTS_DECLARE_CLASS()
private:
	ref<const Texture> m_specularReflectance;
	ref<const Texture> m_diffuseReflectance;
	ref<Shader> m_specularReflectanceShader;
	ref<Shader> m_diffuseReflectanceShader;
	Float m_alpha, m_extIOR, m_intIOR, m_R0;
};

Shader *SmoothPlastic::createShader(Renderer *renderer) const { 
	return new SmoothPlasticShader(renderer,
		m_specularReflectance.get(), m_diffuseReflectance.get(), m_extIOR, m_intIOR);
}

MTS_IMPLEMENT_CLASS(SmoothPlasticShader, false, Shader)

MTS_IMPLEMENT_CLASS_S(SmoothPlastic, false, BSDF)
MTS_EXPORT_PLUGIN(SmoothPlastic, "Smooth plastic BRDF");
MTS_NAMESPACE_END