361 lines
13 KiB
C++
361 lines
13 KiB
C++
/*
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This file is part of Mitsuba, a physically based rendering system.
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Copyright (c) 2007-2011 by Wenzel Jakob and others.
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Mitsuba is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License Version 3
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as published by the Free Software Foundation.
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Mitsuba is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <mitsuba/render/bsdf.h>
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#include <mitsuba/hw/basicshader.h>
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MTS_NAMESPACE_BEGIN
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/*!\plugin{roughdiffuse}{Rough diffuse material}
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* \order{2}
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* \parameters{
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* \parameter{reflectance}{\Spectrum\Or\Texture}{
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* Specifies the diffuse albedo of the
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* material. \default{0.5}
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* }
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* \parameter{alpha}{\Spectrum\Or\Texture}{
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* Specifies the roughness of the unresolved surface micro-geometry
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* using the \emph{root mean square} (RMS) slope of the
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* microfacets. \default{0.2}
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* }
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* \parameter{useFastApprox}{\Boolean}{
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* This parameter selects between the full version of the model
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* or a fast approximation that still retains most qualitative features.
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* \default{\texttt{false}, i.e. use the high-quality version}
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* }
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* }
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*
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* \renderings{
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* \rendering{Smooth diffuse surface ($\alpha=0$)}
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* {bsdf_roughdiffuse_0}
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* \rendering{Very rough diffuse surface ($\alpha=0.7$)}
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* {bsdf_roughdiffuse_0_7}
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* \vspace{-3mm}
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* \caption{The effect of switching from smooth to rough diffuse scattering
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* is fairly subtle on this model---generally, there will be higher
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* reflectance at grazing angles, as well as an overall reduced contrast.}\vspace{3mm}
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* }
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*
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* This reflectance model describes the interaction of light with a \emph{rough}
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* diffuse material, such as plaster, sand, clay, or concrete.
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* The underlying theory was developed by Oren and Nayar
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* \cite{Oren1994Generalization}, who model the microscopic surface structure as
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* unresolved planar facets arranged in V-shaped grooves, where each facet
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* is an ideal diffuse reflector. The model takes into account shadowing,
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* masking, as well as interreflections between the facets.
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*
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* Since the original publication, this approach has been shown to
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* be a good match for many real-world materials, particularly compared
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* to Lambertian scattering, which does not take surface roughness into account.
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*
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* The implementation in Mitsuba uses a surface roughness parameter $\alpha$ that
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* is slightly different from the slope-area variance in the original 1994 paper.
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* The reason for this change is to make the parameter $\alpha$ portable
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* across different models (i.e. \pluginref{roughdielectric}, \pluginref{roughplastic},
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* \pluginref{roughconductor}).
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*
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* To get an intuition about the effect of the
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* parameter $\alpha$, consider the following approximate differentiation:
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* a value of $\alpha=0.001-0.01$ corresponds to a material
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* with slight imperfections on an otherwise smooth surface (for such small
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* values, the model will behave identically to \pluginref{diffuse}), $\alpha=0.1$
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* is relatively rough, and $\alpha=0.3-0.7$ is \emph{extremely} rough
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* (e.g. an etched or ground surface).
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*
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* Note that this material is one-sided---that is, observed from the
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* back side, it will be completely black. If this is undesirable,
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* consider using the \pluginref{twosided} BRDF adapter plugin.
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*/
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class RoughDiffuse : public BSDF {
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public:
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RoughDiffuse(const Properties &props)
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: BSDF(props) {
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/* For better compatibility with other models, support both
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'reflectance' and 'diffuseReflectance' as parameter names */
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m_reflectance = new ConstantSpectrumTexture(props.getSpectrum(
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props.hasProperty("reflectance") ? "reflectance"
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: "diffuseReflectance", Spectrum(0.5f)));
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m_useFastApprox = props.getBoolean("useFastApprox", false);
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m_alpha = new ConstantFloatTexture(props.getFloat("alpha", 0.2f));
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}
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RoughDiffuse(Stream *stream, InstanceManager *manager)
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: BSDF(stream, manager) {
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m_reflectance = static_cast<Texture *>(manager->getInstance(stream));
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m_alpha = static_cast<Texture *>(manager->getInstance(stream));
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m_useFastApprox = stream->readBool();
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configure();
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}
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void configure() {
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/* Verify the input parameter and fix them if necessary */
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m_reflectance = ensureEnergyConservation(m_reflectance, "reflectance", 1.0f);
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m_components.clear();
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m_components.push_back(EGlossyReflection | EFrontSide
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| ((!m_reflectance->isConstant() || !m_alpha->isConstant())
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? ESpatiallyVarying : 0));
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m_usesRayDifferentials = m_reflectance->usesRayDifferentials() ||
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m_alpha->usesRayDifferentials();
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BSDF::configure();
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}
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Spectrum getDiffuseReflectance(const Intersection &its) const {
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return m_reflectance->getValue(its);
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}
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Spectrum eval(const BSDFQueryRecord &bRec, EMeasure measure) const {
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if (!(bRec.typeMask & EGlossyReflection) || measure != ESolidAngle
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|| Frame::cosTheta(bRec.wi) <= 0
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|| Frame::cosTheta(bRec.wo) <= 0)
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return Spectrum(0.0f);
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/* Conversion from Beckmann-style RMS roughness to
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Oren-Nayar-style slope-area variance. The factor
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of 1/sqrt(2) was found to be a perfect fit up
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to extreme roughness values (>.5), after which
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the match is not as good anymore */
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const Float conversionFactor = 1 / std::sqrt((Float) 2);
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Float sigma = m_alpha->getValue(bRec.its).average()
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* conversionFactor;
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const Float sigma2 = sigma*sigma;
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Float sinThetaI = Frame::sinTheta(bRec.wi),
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sinThetaO = Frame::sinTheta(bRec.wo);
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Float cosPhiDiff = 0;
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if (sinThetaI > Epsilon && sinThetaO > Epsilon) {
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/* Compute cos(phiO-phiI) using the half-angle formulae */
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Float sinPhiI = Frame::sinPhi(bRec.wi),
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cosPhiI = Frame::cosPhi(bRec.wi),
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sinPhiO = Frame::sinPhi(bRec.wo),
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cosPhiO = Frame::cosPhi(bRec.wo);
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cosPhiDiff = cosPhiI * cosPhiO + sinPhiI * sinPhiO;
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}
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if (m_useFastApprox) {
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Float A = 1.0f - 0.5f * sigma2 / (sigma2 + 0.33f),
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B = 0.45f * sigma2 / (sigma2 + 0.09f),
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sinAlpha, tanBeta;
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if (Frame::cosTheta(bRec.wi) > Frame::cosTheta(bRec.wo)) {
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sinAlpha = sinThetaO;
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tanBeta = sinThetaI / Frame::cosTheta(bRec.wi);
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} else {
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sinAlpha = sinThetaI;
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tanBeta = sinThetaO / Frame::cosTheta(bRec.wo);
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}
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return m_reflectance->getValue(bRec.its)
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* (INV_PI * Frame::cosTheta(bRec.wo) * (A + B
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* std::max(cosPhiDiff, (Float) 0.0f) * sinAlpha * tanBeta));
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} else {
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Float sinThetaI = Frame::sinTheta(bRec.wi),
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sinThetaO = Frame::sinTheta(bRec.wo),
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thetaI = std::acos(Frame::cosTheta(bRec.wi)),
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thetaO = std::acos(Frame::cosTheta(bRec.wo)),
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alpha = std::max(thetaI, thetaO),
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beta = std::min(thetaI, thetaO);
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Float sinAlpha, sinBeta, tanBeta;
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if (Frame::cosTheta(bRec.wi) > Frame::cosTheta(bRec.wo)) {
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sinAlpha = sinThetaO; sinBeta = sinThetaI;
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tanBeta = sinThetaI / Frame::cosTheta(bRec.wi);
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} else {
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sinAlpha = sinThetaI; sinBeta = sinThetaO;
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tanBeta = sinThetaO / Frame::cosTheta(bRec.wo);
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}
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Float tmp = sigma2 / (sigma2 + 0.09f),
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tmp2 = (4*INV_PI*INV_PI) * alpha * beta,
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tmp3 = 2*beta*INV_PI;
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Float C1 = 1.0f - 0.5f * sigma2 / (sigma2 + 0.33f),
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C2 = 0.45f * tmp,
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C3 = 0.125f * tmp * tmp2 * tmp2,
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C4 = 0.17f * sigma2 / (sigma2 + 0.13f);
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if (cosPhiDiff > 0)
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C2 *= sinAlpha;
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else
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C2 *= sinAlpha - tmp3*tmp3*tmp3;
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/* Compute tan(0.5 * (alpha+beta)) using the half-angle formulae */
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Float tanHalf = (sinAlpha + sinBeta) / (
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std::sqrt(std::max((Float) 0.0f, 1.0f - sinAlpha * sinAlpha)) +
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std::sqrt(std::max((Float) 0.0f, 1.0f - sinBeta * sinBeta)));
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Spectrum rho = m_reflectance->getValue(bRec.its),
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snglScat = rho * (C1 + cosPhiDiff * C2 * tanBeta +
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(1.0f - std::abs(cosPhiDiff)) * C3 * tanHalf),
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dblScat = rho * rho * (C4 * (1.0f - cosPhiDiff*tmp3*tmp3));
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return (snglScat + dblScat) * (INV_PI * Frame::cosTheta(bRec.wo));
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}
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}
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Float pdf(const BSDFQueryRecord &bRec, EMeasure measure) const {
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if (!(bRec.typeMask & EGlossyReflection) || measure != ESolidAngle
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|| Frame::cosTheta(bRec.wi) <= 0
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|| Frame::cosTheta(bRec.wo) <= 0)
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return 0.0f;
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return Frame::cosTheta(bRec.wo) * INV_PI;
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}
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Spectrum sample(BSDFQueryRecord &bRec, const Point2 &sample) const {
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if (!(bRec.typeMask & EGlossyReflection) || Frame::cosTheta(bRec.wi) <= 0)
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return Spectrum(0.0f);
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bRec.wo = squareToHemispherePSA(sample);
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bRec.sampledComponent = 0;
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bRec.sampledType = EGlossyReflection;
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return eval(bRec, ESolidAngle) /
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(Frame::cosTheta(bRec.wo) * INV_PI);
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}
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Spectrum sample(BSDFQueryRecord &bRec, Float &pdf, const Point2 &sample) const {
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if (!(bRec.typeMask & EGlossyReflection) || Frame::cosTheta(bRec.wi) <= 0)
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return Spectrum(0.0f);
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bRec.wo = squareToHemispherePSA(sample);
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bRec.sampledComponent = 0;
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bRec.sampledType = EGlossyReflection;
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pdf = Frame::cosTheta(bRec.wo) * INV_PI;
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return eval(bRec, ESolidAngle);
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}
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void addChild(const std::string &name, ConfigurableObject *child) {
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if (child->getClass()->derivesFrom(MTS_CLASS(Texture))) {
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if (name == "reflectance" || name == "diffuseReflectance")
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m_reflectance = static_cast<Texture *>(child);
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if (name == "alpha")
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m_alpha = static_cast<Texture *>(child);
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else
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BSDF::addChild(name, child);
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} else {
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BSDF::addChild(name, child);
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}
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}
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void serialize(Stream *stream, InstanceManager *manager) const {
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BSDF::serialize(stream, manager);
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manager->serialize(stream, m_reflectance.get());
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manager->serialize(stream, m_alpha.get());
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stream->writeBool(m_useFastApprox);
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}
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std::string toString() const {
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std::ostringstream oss;
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oss << "RoughDiffuse[" << endl
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<< " name = \"" << getName() << "\"," << endl
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<< " reflectance = " << indent(m_reflectance->toString()) << "," << endl
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<< " alpha = " << indent(m_alpha->toString()) << "," << endl
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<< " useFastApprox = " << m_useFastApprox << endl
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<< "]";
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return oss.str();
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}
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Shader *createShader(Renderer *renderer) const;
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MTS_DECLARE_CLASS()
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private:
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ref<Texture> m_reflectance;
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ref<Texture> m_alpha;
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bool m_useFastApprox;
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};
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// ================ Hardware shader implementation ================
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class RoughDiffuseShader : public Shader {
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public:
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RoughDiffuseShader(Renderer *renderer, const Texture *reflectance, const Texture *alpha)
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: Shader(renderer, EBSDFShader), m_reflectance(reflectance), m_alpha(alpha) {
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m_reflectanceShader = renderer->registerShaderForResource(m_reflectance.get());
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m_alphaShader = renderer->registerShaderForResource(m_alpha.get());
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}
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bool isComplete() const {
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return m_reflectanceShader.get() != NULL &&
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m_alphaShader.get() != NULL;
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}
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void cleanup(Renderer *renderer) {
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renderer->unregisterShaderForResource(m_reflectance.get());
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renderer->unregisterShaderForResource(m_alpha.get());
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}
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void putDependencies(std::vector<Shader *> &deps) {
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deps.push_back(m_reflectanceShader.get());
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deps.push_back(m_alphaShader.get());
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}
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void generateCode(std::ostringstream &oss,
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const std::string &evalName,
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const std::vector<std::string> &depNames) const {
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oss << "vec3 " << evalName << "(vec2 uv, vec3 wi, vec3 wo) {" << endl
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<< " if (cosTheta(wi) <= 0.0 || cosTheta(wo) <= 0.0)" << endl
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<< " return vec3(0.0);" << endl
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<< " float sigma = " << depNames[1] << "(uv)[0] * 0.70711;" << endl
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<< " float sigma2 = sigma * sigma;" << endl
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<< " float A = 1.0 - 0.5 * sigma2 / (sigma2 + 0.33);" << endl
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<< " float B = 0.45 * sigma2 / (sigma2 + 0.09);" << endl
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<< " float maxCos = max(0.0, cosPhi(wi)*cosPhi(wo)+sinPhi(wi)*sinPhi(wo));" << endl
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<< " float sinAlpha, tanBeta;" << endl
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<< " if (cosTheta(wi) > cosTheta(wo)) {" << endl
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<< " sinAlpha = sinTheta(wo);" << endl
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<< " tanBeta = sinTheta(wi) / cosTheta(wi);" << endl
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<< " } else {" << endl
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<< " sinAlpha = sinTheta(wi);" << endl
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<< " tanBeta = sinTheta(wo) / cosTheta(wo);" << endl
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<< " }" << endl
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<< " float value = A + B * maxCos * sinAlpha * tanBeta;" << endl
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<< " return " << depNames[0] << "(uv) * 0.31831 * cosTheta(wo) * value;" << endl
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<< "}" << endl
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<< endl
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<< "vec3 " << evalName << "_diffuse(vec2 uv, vec3 wi, vec3 wo) {" << endl
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<< " if (cosTheta(wi) <= 0.0 || cosTheta(wo) <= 0.0)" << endl
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<< " return vec3(0.0);" << endl
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<< " return " << depNames[0] << "(uv) * 0.31831 * cosTheta(wo);" << endl
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<< "}" << endl;
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}
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MTS_DECLARE_CLASS()
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private:
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ref<const Texture> m_reflectance;
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ref<const Texture> m_alpha;
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ref<Shader> m_reflectanceShader;
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ref<Shader> m_alphaShader;
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};
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Shader *RoughDiffuse::createShader(Renderer *renderer) const {
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return new RoughDiffuseShader(renderer, m_reflectance.get(), m_alpha.get());
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}
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MTS_IMPLEMENT_CLASS(RoughDiffuseShader, false, Shader)
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MTS_IMPLEMENT_CLASS_S(RoughDiffuse, false, BSDF)
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MTS_EXPORT_PLUGIN(RoughDiffuse, "Rough diffuse BRDF")
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MTS_NAMESPACE_END
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