a few bugfixed, re-integrated twosided

data/tests/test_bsdf.xml

@@ -8,6 +8,11 @@
 	<!-- Test the rough diffuse model -->
 	<bsdf type="roughdiffuse"/>
 
+	<!-- Test the two-sided model -->
+	<bsdf type="twosided">
+		<bsdf type="diffuse"/>
+	</bsdf>
+
 	<!-- Test the diffuse transmission model -->
 	<bsdf type="difftrans"/>
 
@@ -110,4 +115,5 @@
 		<string name="distribution" value="beckmann"/>
 		<float name="alpha" value=".7"/>
 	</bsdf>
+
 </scene>

doc/main.bib

@@ -46,3 +46,15 @@
 	year      = {1994},
 	organization={ACM}
 }
+
+@inproceedings{Weidlich2007Arbitrarily,
+	author = {Weidlich, Andrea and Wilkie, Alexander},
+	title = {Arbitrarily layered micro-facet surfaces},
+	booktitle = {Proceedings of the 5th international conference on Computer graphics and interactive techniques in Australia and Southeast Asia},
+	series = {GRAPHITE '07},
+	year = {2007},
+	pages = {171--178},
+	publisher = {ACM},
+	address = {New York, NY, USA}
+} 
+

src/bsdfs/SConscript

@@ -12,15 +12,15 @@ plugins += env.SharedLibrary('roughplastic', ['roughplastic.cpp'])
 
 # Materials that act as modifiers
 #plugins += env.SharedLibrary('coating', ['coating.cpp'])
-#plugins += env.SharedLibrary('twosided', ['twosided.cpp'])
+plugins += env.SharedLibrary('twosided', ['twosided.cpp'])
 #plugins += env.SharedLibrary('mask', ['mask.cpp'])
 plugins += env.SharedLibrary('mixture', ['mixture.cpp'])
 
 
 # Other materials
 plugins += env.SharedLibrary('difftrans', ['difftrans.cpp'])
+plugins += env.SharedLibrary('phong', ['phong.cpp'])
 #plugins += env.SharedLibrary('ward', ['ward.cpp'])
-#plugins += env.SharedLibrary('phong', ['phong.cpp'])
 #plugins += env.SharedLibrary('irawan', ['irawan.cpp'])
 
 Export('plugins')

src/bsdfs/coating.cpp

@@ -27,6 +27,7 @@ MTS_NAMESPACE_BEGIN
  *     \parameter{intIOR}{\Float}{Interior index of refraction \default{1.5046}}
  *     \parameter{extIOR}{\Float}{Exterior index of refraction \default{1.0}}
  * }
+ * This class implements a smooth dielectric coating in the style of \cite{Weidlich2007Arbitrarily}.
  *
  *  XXX cancel out cosine factors?
  *  XXX did I get the measure conversion terms right?

src/bsdfs/microfacet.h

@@ -460,7 +460,7 @@ public:
 
 			nEvalsTotal += nEvals;
 		}
-		SLog(EInfo, "Created a " SIZE_T_FMT "-node cubic spline approximation to the rough Frensel "
+		SLog(EInfo, "Created a " SIZE_T_FMT "-node cubic spline approximation to the rough Fresnel "
 				"transmittance (integration took %i ms and " SIZE_T_FMT " function evaluations)",
 				resolution, timer->getMilliseconds(), nEvalsTotal);
 		spline->build();

src/bsdfs/roughconductor.cpp

@@ -36,6 +36,7 @@ MTS_NAMESPACE_BEGIN
  *           \item \code{ggx}: New distribution proposed by
  *              Walter et al. \cite{Walter07Microfacet}, which is meant to better handle 
  *              the long tails observed in measurements of ground surfaces. 
+ *              Renderings with this distribution may converge slowly.
  *           \item \code{phong}: Classical $\cos^p\theta$ distribution.
  *              Due to the underlying microfacet theory, 
  *              the use of this distribution here leads to more realistic 
@@ -67,13 +68,9 @@ MTS_NAMESPACE_BEGIN
  *         factor used to modulate the reflectance component\default{1.0}}
  * }
  * This plugin implements a realistic microfacet scattering model for rendering
- * rough conducting materials, such as metals. Microfacet theory describes rough 
+ * rough conducting materials, such as metals. It can be interpreted as a fancy 
- * surfaces as an arrangement of unresolved and ideally specular facets, whose 
+ * version of the Cook-Torrance model and should be preferred over 
- * normal directions are given by a specially chosen \emph{microfacet distribution}. 
+ * empirical models like \pluginref{phong} and \pluginref{ward} when possible.
- * By accounting for shadowing and masking effects between these facets, it is 
- * possible to reproduce the important off-specular reflections peaks observed 
- * in real-world measurements of such materials.
-
  * \renderings{
  *     \rendering{Rough copper (Beckmann, $\alpha=0.1$)}
  *     	   {bsdf_roughconductor_copper.jpg}
@@ -81,9 +78,16 @@ MTS_NAMESPACE_BEGIN
  *         $\alpha_u=0.05,\ \alpha_v=0.3$), see 
  *         \lstref{roughconductor-aluminium}}
  *         {bsdf_roughconductor_anisotropic_aluminium.jpg}
- *     \vspace{-7mm}
+ *     \vspace{-8mm}
  * }
  *
+ * Microfacet theory describes rough 
+ * surfaces as an arrangement of unresolved and ideally specular facets, whose 
+ * normal directions are given by a specially chosen \emph{microfacet distribution}. 
+ * By accounting for shadowing and masking effects between these facets, it is 
+ * possible to reproduce the important off-specular reflections peaks observed 
+ * in real-world measurements of such materials.
+ *
  * This plugin is essentially the ``roughened'' equivalent of the (smooth) plugin
  * \pluginref{conductor}. For very low values of $\alpha$, the two will
  * be very similar, though scenes using this plugin will take longer to render 
@@ -108,8 +112,8 @@ MTS_NAMESPACE_BEGIN
  * with slight imperfections on an
  * otherwise smooth surface finish, $\alpha=0.1$ is relatively rough,
  * and $\alpha=0.3-0.7$ is \emph{extremely} rough (e.g. an etched or ground
- * finish).
+ * finish). Values significantly above that are probably not too realistic.
- * \vspace{-2mm}
+ * \vspace{-6mm}
  * \subsubsection*{Techical details}\vspace{-2mm}
  * When rendering with the Ashikhmin-Shirley or Phong microfacet 
  * distributions, a conversion is used to turn the specified 
@@ -122,7 +126,7 @@ MTS_NAMESPACE_BEGIN
  * of two distinct roughness values along the tangent and bitangent
  * directions. This can be used to provide a material with a ``brushed''
  * appearance. The alignment of the anisotropy will follow the UV
- * parameterization of the underlying mesh in this case. This means that
+ * parameterization of the underlying mesh in this case. This also means that
  * such an anisotropic material cannot be applied to triangle meshes that 
  * are missing texture coordinates.
  *
@@ -131,7 +135,7 @@ MTS_NAMESPACE_BEGIN
  * in RGB mode, the computations will be much more approximate in this case.
  * Also note that this material is one-sided---that is, observed from the 
  * back side, it will be completely black. If this is undesirable, 
- * consider using the \pluginref{twosided} BRDF adapter plugin.
+ * consider using the \pluginref{twosided} BRDF adapter.
  *
  * \begin{xml}[caption={A material definition for brushed aluminium}, label=lst:roughconductor-aluminium]
  * <bsdf type="roughconductor">
@@ -310,10 +314,11 @@ public:
 		const Spectrum F = fresnelConductor(Frame::cosTheta(bRec.wi),
 				m_eta, m_k);
 
-		Float numerator = m_distribution.G(bRec.wi, bRec.wo, m, alphaU, alphaV)
+		Float numerator = m_distribution.eval(m, alphaU, alphaV)
+			* m_distribution.G(bRec.wi, bRec.wo, m, alphaU, alphaV)
 			* dot(bRec.wi, m);
 
-		Float denominator = Frame::cosTheta(m)
+		Float denominator = m_distribution.pdf(m, alphaU, alphaV)
 			* Frame::cosTheta(bRec.wi);
 
 		return m_specularReflectance->getValue(bRec.its) * F

src/bsdfs/roughdielectric.cpp

@@ -135,7 +135,7 @@ MTS_NAMESPACE_BEGIN
  * of two distinct roughness values along the tangent and bitangent
  * directions. This can be used to provide a material with a ``brushed''
  * appearance. The alignment of the anisotropy will follow the UV
- * parameterization of the underlying mesh in this case. This means that
+ * parameterization of the underlying mesh in this case. This also means that
  * such an anisotropic material cannot be applied to triangle meshes that 
  * are missing texture coordinates.\newpage
  *

src/bsdfs/roughplastic.cpp

@@ -53,7 +53,7 @@ MTS_NAMESPACE_BEGIN
  *         \default{0.1}. 
  *     }
  *     \parameter{intIOR}{\Float\Or\String}{Interior index of refraction specified
- *      numerically or using a known material name. \default{\texttt{bk7} / 1.5046}}
+ *      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
@@ -62,10 +62,73 @@ MTS_NAMESPACE_BEGIN
  *         factor used to modulate the diffuse reflectance component\default{0.5}}
  * }
  * \renderings{
- *     \rendering{Beckmann, $\alpha=0.1$}{bsdf_roughplastic_ggx}
+ *     \medrendering{Beckmann, $\alpha=0.05$, \texttt{diffuse}
- *     \rendering{GGX, $\alpha=0.3$}{bsdf_roughplastic_ggx}
+ *         \showbreak\texttt{Reflectance=0}, \lstref{roughplastic-lacquer}}{bsdf_roughplastic_beckmann_lacquer}
+ *     \medrendering{Beckmann, $\alpha=0.1$}{bsdf_roughplastic_beckmann}
+ *     \medrendering{GGX, $\alpha=0.3$}{bsdf_roughplastic_ggx}
  * }
  *
+ * This plugin implements a realistic microfacet scattering model for rendering
+ * rough dielectric materials with internal scattering, such as plastic. It can 
+ * be interpreted as a fancy version of the Cook-Torrance model and should be 
+ * preferred over empirical models like \pluginref{phong} and \pluginref{ward} 
+ * when possible.
+ *
+ * Microfacet theory describes rough surfaces as an arrangement of unresolved and 
+ * ideally specular facets, whose normal directions are given by a specially
+ * chosen \emph{microfacet distribution}. 
+ * By accounting for shadowing and masking effects between these facets, it is 
+ * possible to reproduce the important off-specular reflections peaks observed 
+ * in real-world measurements of such materials.
+ *
+ * This plugin is essentially the ``roughened'' equivalent of the (smooth) plugin
+ * \pluginref{plastic}. For very low values of $\alpha$, the two will
+ * be very similar, though scenes using this plugin will take longer to render 
+ * due to the additional computational burden of tracking surface roughness.
+ *
+ * The model uses the integrated specular reflectance to interpolate between the 
+ * specular and diffuse components (i.e. any light that is not scattered
+ * specularly is assumed to contribute to the diffuse component).
+ * 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). 
+ * 
+ * The implementation is based on the paper ``Microfacet Models
+ * for Refraction through Rough Surfaces'' by Walter et al. 
+ * \cite{Walter07Microfacet}. It supports several different types of microfacet
+ * distributions. Note that the choices are a bit more restricted here---in 
+ * comparison to other rough scattering models in Mitsuba,
+ * the roughness cannot be textured, and anisotropic microfacet 
+ * distributions are not allowed.
+ *
+ * When no parameters are given, the plugin activates the default settings, 
+ * which describe a white polypropylene plastic material with a light amount
+ * of roughness modeled using the Beckmann distribution.
+ *
+ * To get an intuition about the effect of the surface roughness
+ * parameter $\alpha$, consider the following approximate differentiation: 
+ * a value of $\alpha=0.001-0.01$ corresponds to a material 
+ * with slight imperfections on an
+ * otherwise smooth surface finish, $\alpha=0.1$ is relatively rough,
+ * and $\alpha=0.3-0.7$ is \emph{extremely} rough (e.g. an etched or ground
+ * finish). Values significantly above that are probably not too realistic.
+*
+ * When rendering with the Phong microfacet 
+ * distributions, a conversion is used to turn the specified 
+ * $\alpha$ roughness value into the Phong exponent.
+ * This is done in a way, such that the different 
+ * distributions all produce a similar appearance for 
+ * the same value of $\alpha$.\vspace{5mm}
+ *
+ * \begin{xml}[caption={A material definition for rough, black laquer.}, label=lst:roughplastic-lacquer]
+ * <bsdf type="roughplastic">
+ *     <string name="distribution" value="beckmann"/>
+ *     <float name="alpha" value="0.05"/>
+ *     <float name="intIOR" value="1.61"/>
+ *     <spectrum name="diffuseReflectance" value="0"/>
+ * </bsdf>
+ * \end{xml}
+*
  */
 class RoughPlastic : public BSDF {
 public:
@@ -76,7 +139,7 @@ public:
 			props.getSpectrum("diffuseReflectance", Spectrum(0.5f)));
 
 		/* Specifies the internal index of refraction at the interface */
-		m_intIOR = lookupIOR(props, "intIOR", "bk7");
+		m_intIOR = lookupIOR(props, "intIOR", "polypropylene");
 
 		/* Specifies the external index of refraction at the interface */
 		m_extIOR = lookupIOR(props, "extIOR", "air");

src/bsdfs/twosided.cpp

@@ -24,7 +24,17 @@ MTS_NAMESPACE_BEGIN
 
 /*! \plugin{twosided}{Two-sided BRDF adapter}
  * 
- * Turns a nested one-sided BRDF onto a two-sided version that
+ * By default, all non-transmissive scattering models in Mitsuba 
+ * are \emph{one-sided} --- in other words, they absorb all light 
+ * that is received on the backs-side or interior of any surfaces 
+ * associated with them. Holes in a mesh will thus be 
+ *
+ * This is usually a good idea, since it will expose modeling
+ * issues early on. But sometimes one is forced to deal with such
+ * a bad mesh. In this case, this plugin that cannot be fixed.
+ * 
+ *
+ * This plugin turns a nested one-sided model onto a two-sided version that
  * can be used to render meshes where the back-side is visible.
  *
  * \begin{xml}
@@ -65,23 +75,22 @@ public:
 				"a transmission component can be nested!");
 	}
 
-	Spectrum eval(const BSDFQueryRecord &bRec) const {
+	Spectrum eval(const BSDFQueryRecord &bRec, EMeasure measure) const {
 		BSDFQueryRecord b(bRec);
 		if (Frame::cosTheta(b.wi) < 0) {
 			b.wi.z *= -1;
 			b.wo.z *= -1;
 		}
-		return m_nestedBRDF->eval(b);
+		return m_nestedBRDF->eval(b, measure);
 	}
 
-
+	Float pdf(const BSDFQueryRecord &bRec, EMeasure measure) const {
-	Float pdf(const BSDFQueryRecord &bRec) const {
 		BSDFQueryRecord b(bRec);
 		if (b.wi.z < 0) {
 			b.wi.z *= -1;
 			b.wo.z *= -1;
 		}
-		return m_nestedBRDF->pdf(b);
+		return m_nestedBRDF->pdf(b, measure);
 	}
 
 	Spectrum sample(BSDFQueryRecord &bRec, const Point2 &sample) const {
@@ -112,7 +121,7 @@ public:
 
 		if (flipped) {
 			bRec.wi.z *= -1;
-	
+
 			if (!result.isZero() && pdf != 0)
 				bRec.wo.z *= -1;
 		}