cleanups

src/bsdfs/conductor.cpp

@@ -26,17 +26,20 @@ MTS_NAMESPACE_BEGIN
  * \parameters{
  *     \parameter{preset}{\String}{Name of a material preset, see 
  *           \tblref{conductor-iors}.\!\default{\texttt{Cu} / copper}}
- *     \parameter{eta}{\Spectrum}{Real part of the material's index of refraction
+ *     \parameter{eta}{\Spectrum}{Real part of the material's index 
- *           \default{based on the value of \texttt{preset}}}
+ *           of refraction \default{based on the value of \texttt{preset}}}
  *     \parameter{k}{\Spectrum}{Imaginary part of the material's index of 
  *             refraction, also known as absorption coefficient.
  *             \default{based on the value of \texttt{preset}}}
- *     \lastparameter{specular\showbreak Reflectance}{\Spectrum\Or\Texture}{Optional
+ *     \lastparameter{specular\showbreak Reflectance}{\Spectrum\Or\Texture}{
- *         factor used to modulate the reflectance component\default{1.0}}
+ *        Optional factor used to modulate the reflectance component
+ *        \default{1.0}}
  * }
  * \renderings{
- *     \rendering{Measured copper material (the default)}{bsdf_conductor_copper.jpg}
+ *     \rendering{Measured copper material (the default)}
- *     \rendering{Measured gold material (\lstref{conductor-gold})}{bsdf_conductor_gold.jpg}
+ *         {bsdf_conductor_copper.jpg}
+ *     \rendering{Measured gold material (\lstref{conductor-gold})}
+ *         {bsdf_conductor_gold.jpg}
  * }
  
  * This plugin implements a perfectly smooth interface to a conducting material, 
@@ -50,18 +53,20 @@ MTS_NAMESPACE_BEGIN
  * 
  * To faciliate the tedious task of specifying spectrally-varying index of 
  * refraction information, Mitsuba ships with a set of measured data for a 
- * several materials, where visible-spectrum information was publicly available\footnote{
+ * several materials, where visible-spectrum information was publicly 
- *   These index of refraction values are identical to the data distributed with PBRT. 
+ * available\footnote{
- *   They are originally from the Luxpop database (\url{www.luxpop.com}) and 
+ *   These index of refraction values are identical to the data distributed 
- *   are based on data by Palik et al. \cite{Palik1998Handbook} and measurements 
+ *   with PBRT. They are originally from the Luxpop database
- *   of atomic scattering factors made by the Center For X-Ray Optics (CXRO) 
+ *   (\url{www.luxpop.com}) and are based on data by Palik et al. 
- *   at Berkeley and the Lawrence Livermore National Laboratory (LLNL).
+ *   \cite{Palik1998Handbook} and measurements of atomic scattering factors 
+ *   made by the Center For X-Ray Optics (CXRO) at Berkeley and the 
+ *   Lawrence Livermore National Laboratory (LLNL).
  * }. 
  * 
- * Note that \tblref{conductor-iors} also includes several popular optical coatings, which are
+ * Note that \tblref{conductor-iors} also includes several popular optical 
- * not actually conductors. These materials can also be used with this plugin,
+ * coatings, which are not actually conductors. These materials can also 
- * though note that the plugin will ignore any refraction component that the actual 
+ * be used with this plugin, though note that the plugin will ignore any 
- * material might have had.
+ * refraction component that the actual material might have had.
  * The table also contains a few birefingent materials, which are split into
  * separate measurements correponding to their two indices of 
  * refraction (named ``ordinary'' and ``extraordinary ray'').
@@ -70,7 +75,8 @@ MTS_NAMESPACE_BEGIN
  * renderings to get the most accurate results. While it also works in RGB mode, 
  * the computations will be much more approximate in this case.
  *
- * \begin{xml}[caption=Material configuration for a smooth conductor with measured gold data, label=lst:conductor-gold]
+ * \begin{xml}[caption=Material configuration for a smooth conductor with 
+ *    measured gold data, label=lst:conductor-gold]
  * <shape type="...">
  *     <bsdf type="conductor">
  *         <string name="preset" value="Au"/>
@@ -79,7 +85,8 @@ MTS_NAMESPACE_BEGIN
  * \end{xml}
  * \vspace{5mm}
  * It is also possible to load spectrally varying index of refraction data from 
- * two external files (see \secref{format-spectra} for details on the file format):
+ * two external files (see \secref{format-spectra} for details on the file 
+ * format):
  * \begin{xml}[caption=Rendering a smooth conductor with custom data]
  * <shape type="...">
  *     <bsdf type="conductor">
@@ -121,12 +128,13 @@ MTS_NAMESPACE_BEGIN
  * \end{tabular}
  * \caption{
  *     \label{tbl:conductor-iors}
- *      This table lists all supported material names that can be passed into the
+ *      This table lists all supported materials that can be passed into the
- *      \pluginref{conductor} plugin. Note that some of them are not actually 
+ *      \pluginref{conductor} and \pluginref{roughconductor} plugins. Note that
- *      conductors---this is not a problem, they can be used regardless (though only
+ *      some of them are not actually conductors---this is not a problem, 
- *      the reflection component and no transmission will be simulated).
+ *      they can be used regardless (though only the reflection component and
- *      In most cases, there are multiple entries for each material, which 
+ *      no transmission will be simulated). In most cases, there are 
- *      represent different measurements.
+ *      multiple entries for each material, which represent measurements by 
+ *      different authors.
  * }
  * \end{table}
  */
@@ -196,9 +204,12 @@ public:
 		bool sampleReflection   = (bRec.typeMask & EDeltaReflection)
 				&& (bRec.component == -1 || bRec.component == 0);
 
+		/* Verify that the provided direction pair matches an ideal
+		   specular reflection; tolerate some roundoff errors */
 		if (!sampleReflection || measure != EDiscrete ||
 			Frame::cosTheta(bRec.wi) <= 0 ||
-			Frame::cosTheta(bRec.wo) <= 0)
+			Frame::cosTheta(bRec.wo) <= 0 ||
+			std::abs(1 - dot(reflect(bRec.wi), bRec.wo)) > Epsilon)
 			return Spectrum(0.0f);
 
 		return m_specularReflectance->getValue(bRec.its) *
@@ -208,10 +219,15 @@ public:
 	Float pdf(const BSDFQueryRecord &bRec, EMeasure measure) const {
 		bool sampleReflection   = (bRec.typeMask & EDeltaReflection)
 				&& (bRec.component == -1 || bRec.component == 0);
+
+		/* Verify that the provided direction pair matches an ideal
+		   specular reflection; tolerate some roundoff errors */
 		if (!sampleReflection || measure != EDiscrete ||
 			Frame::cosTheta(bRec.wi) <= 0 ||
-			Frame::cosTheta(bRec.wo) <= 0)
+			Frame::cosTheta(bRec.wo) <= 0 ||
+			std::abs(1 - dot(reflect(bRec.wi), bRec.wo)) > Epsilon)
 			return 0.0f;
+
 		return 1.0f;
 	}
 

src/bsdfs/dielectric.cpp

@@ -45,14 +45,14 @@ MTS_NAMESPACE_BEGIN
  *
  * This plugin models an interface between two dielectric materials having mismatched 
  * indices of refraction (for instance, water and air). Exterior and interior IOR values
- * can each be independently specified, where ``exterior'' refers to the side that contains 
+ * can be independently specified, where ``exterior'' refers to the side that contains 
  * the surface normal. When no parameters are given, the plugin activates the defaults, which
  * describe a borosilicate glass BK7/air interface.
  *
- * In this model, the microscopic surface structure of the surface is assumed to be perfectly 
+ * In this model, the microscopic structure of the surface is assumed to be perfectly 
  * smooth, resulting in a degenerate\footnote{Meaning that for any given incoming ray of light,
  * the model always scatters into a discrete set of directions, as opposed to a continuum.} 
- * BSDF described by a Dirac delta function. For a similar model that instead describes a 
+ * BSDF described by a Dirac delta distribution. For a similar model that instead describes a 
  * rough surface microstructure, take a look at the \pluginref{roughdielectric} plugin. 
  *
  * \begin{xml}[caption=A simple air-to-water interface, label=lst:dielectric-water]
@@ -125,9 +125,13 @@ MTS_NAMESPACE_BEGIN
  *     \end{tabular}
  *     \caption{
  *         \label{tbl:dielectric-iors}
- *          This table lists all supported material names that can be passed
+ *          This table lists all supported material names along with
- *          into the \pluginref{dielectric} plugin, along with the associated 
+ *          along with the associated index of refraction at 
- *          index of refraction at standard conditions.
+ *          standard conditions. These can be used with the plugins
+ *          \pluginref{dielectric},\
+ *          \pluginref{roughdielectric},\
+ *          \pluginref{plastic}, and
+ *          \pluginref{roughplastic}.
  *     }
  * \end{table}
  */
@@ -200,26 +204,66 @@ public:
 		return Vector(-wi.x, -wi.y, wi.z);
 	}
 
-	/// Refraction in local coordinates
+	/// Refraction in local coordinates (reuses computed information)
 	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) 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);
+
+		Float cosThetaT = 0;
+		if (sinThetaTSqr >= 1.0f) {
+			/* Total internal reflection */
+			return Vector(0.0f);
+		} else {
+			cosThetaT = std::sqrt(1.0f - sinThetaTSqr);
+
+			if (entering)
+				cosThetaT = -cosThetaT;
+		}
+
+		return Vector(-eta*wi.x, -eta*wi.y, cosThetaT);
+	}
+
 	Spectrum eval(const BSDFQueryRecord &bRec, EMeasure measure) const {
 		bool sampleReflection   = (bRec.typeMask & EDeltaReflection)
 				&& (bRec.component == -1 || bRec.component == 0);
 		bool sampleTransmission = (bRec.typeMask & EDeltaTransmission)
 				&& (bRec.component == -1 || bRec.component == 1);
-		bool reflection = Frame::cosTheta(bRec.wo) * Frame::cosTheta(bRec.wi) > 0;
 
-		if ((reflection && !sampleReflection) || 
+		/* Check if the provided direction pair matches an ideal
-		   (!reflection && !sampleTransmission) || measure != EDiscrete)
+		   specular reflection; tolerate some roundoff errors */
+		bool reflection = std::abs(1 - dot(reflect(bRec.wi), bRec.wo)) < Epsilon;
+		if (measure != EDiscrete || (reflection && !sampleReflection))
 			return Spectrum(0.0f);
 
-		Float fr = fresnel(Frame::cosTheta(bRec.wi), m_extIOR, m_intIOR);
+		if (!reflection) {
+			/* Check if the provided direction pair matches an ideal
+			   specular refraction; tolerate some roundoff errors */
+			bool refraction = std::abs(1 - dot(refract(bRec.wi), bRec.wo)) < Epsilon;
+			if (!refraction || !sampleTransmission)
+				return Spectrum(0.0f);
+		}
+
+		Float Fr = fresnel(Frame::cosTheta(bRec.wi), m_extIOR, m_intIOR);
 
 		if (reflection) {
-			return m_specularReflectance->getValue(bRec.its) * fr;
+			return m_specularReflectance->getValue(bRec.its) * Fr;
 		} else {
 			Float etaI = m_extIOR, etaT = m_intIOR;
 			bool entering = Frame::cosTheta(bRec.wi) > 0.0f;
@@ -229,7 +273,7 @@ public:
 			Float factor = (bRec.quantity == ERadiance) 
 				? (etaI*etaI) / (etaT*etaT) : 1.0f;
 
-			return m_specularTransmittance->getValue(bRec.its)  * factor * (1 - fr);
+			return m_specularTransmittance->getValue(bRec.its)  * factor * (1 - Fr);
 		}
 	}
 
@@ -238,13 +282,21 @@ public:
 				&& (bRec.component == -1 || bRec.component == 0);
 		bool sampleTransmission = (bRec.typeMask & EDeltaTransmission)
 				&& (bRec.component == -1 || bRec.component == 1);
-		bool reflection = Frame::cosTheta(bRec.wo)
-			* Frame::cosTheta(bRec.wi) > 0;
 
-		if ((reflection && !sampleReflection) || 
+		/* Check if the provided direction pair matches an ideal
-		   (!reflection && !sampleTransmission) || measure != EDiscrete)
+		   specular reflection; tolerate some roundoff errors */
+		bool reflection = std::abs(1 - dot(reflect(bRec.wi), bRec.wo)) < Epsilon;
+		if (measure != EDiscrete || (reflection && !sampleReflection))
 			return 0.0f;
 
+		if (!reflection) {
+			/* Check if the provided direction pair matches an ideal
+			   specular refraction; tolerate some roundoff errors */
+			bool refraction = std::abs(1 - dot(refract(bRec.wi), bRec.wo)) < Epsilon;
+			if (!refraction || !sampleTransmission)
+				return 0.0f;
+		}
+
 		if (sampleTransmission && sampleReflection) {
 			Float Fr = fresnel(Frame::cosTheta(bRec.wi), m_extIOR, m_intIOR);
 			return reflection ? Fr : (1 - Fr);

src/bsdfs/roughdielectric.cpp

@@ -43,10 +43,9 @@ MTS_NAMESPACE_BEGIN
  *              behavior than the separately available \pluginref{phong} plugin.
  *           \item \code{ggx}: New distribution proposed by
  *              Walter et al. meant to better handle the long
- *              tails observed in transmission measurements through
+ *              tails observed in measurements of ground surfaces. 
- *              ground glass. Renderings with this distribution may
+ *              Renderings with this distribution may converge slowly.
- *              converge slowly.
+ *           \item \code{as}: Anisotropic Phong-style microfacet distribution proposed by
- *           \item \code{as}: Anisotropic microfacet distribution proposed by
  *              Ashikhmin and Shirley \cite{Ashikhmin2005Anisotropic}.\vspace{-3mm}
  *       \end{enumerate}
  *     }
@@ -58,12 +57,14 @@ MTS_NAMESPACE_BEGIN
  *         \default{0.1}. 
  *     }
  *     \parameter{alphaU, alphaV}{\Float\Or\Texture}{
- *         Specifies the anisotropic rougness values along the tangent and bitangent directions. This
+ *         Specifies the anisotropic rougness values along the tangent and bitangent directions. These
- *         parameter is only valid when \texttt{distribution=as}.
+ *         parameter are only valid when \texttt{distribution=as}.
  *         \default{0.1}. 
  *     }
- *     \parameter{intIOR}{\Float}{Interior index of refraction \default{1.5046}}
+ *     \parameter{intIOR}{\Float\Or\String}{Interior index of refraction specified
- *     \parameter{extIOR}{\Float}{Exterior index of refraction \default{1.0}}
+ *      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{specular\showbreak Reflectance}{\Spectrum\Or\Texture}{Optional
  *         factor used to modulate the reflectance component\default{1.0}}
  *     \lastparameter{specular\showbreak Transmittance}{\Spectrum\Or\Texture}{Optional
@@ -93,39 +94,43 @@ MTS_NAMESPACE_BEGIN
  * plugin is based on the paper ``Microfacet Models for Refraction through 
  * Rough Surfaces'' by Walter et al. \cite{Walter07Microfacet}. It supports 
  * several types of microfacet distributions and has a texturable roughness 
- * parameter.  Exterior and interior IOR values can each be independently 
+ * parameter.  Exterior and interior IOR values can be independently 
  * specified, where ``exterior'' refers to the side that contains the surface
- * normal. When no parameters are given, the plugin activates the default 
+ * normal. Similar to the \pluginref{dielectric} plugin, IOR values can either
- * settings, which describe a borosilicate glass BK7/air interface with a 
+ * be specified numerically, or based on a list of known materials (see
- * light amount of roughness modeled using a Beckmann distribution.
+ * \tblref{dielectric-iors} for an overview). When no parameters are given, 
+ * the plugin activates the default settings, which describe a borosilicate 
+ * glass BK7/air interface with a light amount of roughness modeled using a 
+ * Beckmann distribution.
  * 
  * When using the Ashikmin-Shirley or Phong models, a conversion method is
  * used to turn the specified $\alpha$ roughness value into the exponents 
- * of these distributions. This is done so that the different distributions 
+ * of these distributions. This is done in a way, such that the different 
- * all produce a similar appearance for the same value of $\alpha$.
+ * distributions all produce a similar appearance for the same value of $\alpha$.
  *
  * When using this plugin, it is crucial that the scene contains
  * meaningful and mutally compatible index of refraction changes---see
  * \figref{glass-explanation} for an example. Also, please note that
  * the importance sampling implementation of this model is close, but 
- * not perfect a perfect match to the underlying scattering distribution,
+ * not always a perfect a perfect match to the underlying scattering distribution,
- * particularly for high roughness values and when the \texttt{GGX} 
+ * particularly for high roughness values and when the \texttt{ggx} 
- * model is used. Hence, such renderings may converge slowly.\vspace{1cm}
+ * microfacet distribution is used. Hence, such renderings may 
+ * converge slowly.\vspace{1cm}
  *
- * \begin{xml}[caption=Material definition for ground glass, label=lst:roughdielectric-roughglass]
+ * \begin{xml}[caption=A material definition for ground glass, label=lst:roughdielectric-roughglass]
  * <bsdf type="roughdielectric">
  *     <string name="distribution" value="ggx"/>
  *     <float name="alpha" value="0.304"/>
- *     <float name="intIOR" value="1.5046"/>
+ *     <string name="intIOR" value="bk7"/>
- *     <float name="extIOR" value="1.0"/>
+ *     <string name="extIOR" value="air"/>
  * </bsdf>
  * \end{xml}
  *
  * \begin{xml}[caption=A texture can be attached to the roughness parameter, label=lst:roughdielectric-textured]
  * <bsdf type="roughdielectric">
  *     <string name="distribution" value="beckmann"/>
- *     <string name="intIOR" value="bk7"/>
+ *     <float name="intIOR" value="1.5046"/>
- *     <string name="extIOR" value="air"/>
+ *     <float name="extIOR" value="1.0"/>
  *
  *     <texture name="alpha" type="bitmap">
  *         <string name="filename" value="roughness.exr"/>