finished the roughdiffuse model, fixed a handedness switch in Transform::lookAt

data/tests/test_bsdf.xml

@@ -5,6 +5,9 @@
 	<!-- Test the smooth diffuse model -->
 	<bsdf type="diffuse"/>
 
+	<!-- Test the rough diffuse model -->
+	<bsdf type="roughdiffuse"/>
+
 	<!-- Test the diffuse transmission model -->
 	<bsdf type="difftrans"/>
 

doc/format.tex

@@ -189,11 +189,10 @@ The \texttt{reflectance} intent is used by default, so remember to
 set it to \texttt{illuminant} when defining the brightness of a
 light source with the \texttt{<rgb>} tag.
 
-When spectral power distributions are obtained from measurements 
+When spectral power or reflectance distributions are obtained from measurements 
 (e.g. at 10$nm$ intervals), they are usually quite unwiedy and can clutter
 the scene description. For this reason, there is yet another way to pass 
-a spectrum by loading it from an external
+a spectrum by loading it from an external file:
-file:
 \begin{xml}
 <spectrum name="spectrumProperty" filename="measuredSpectrum.spd"/>
 \end{xml}
@@ -201,7 +200,7 @@ The file should contain a single measurement per line, with the corresponding
 wavelength in nanometers and the measured value separated by a space. Comments
 are allowed. Here is an example:
 \begin{xml}
-# This file contains a measured spectral power distribution
+# This file contains a measured spectral power/reflectance distribution
 406.13 0.703313
 413.88 0.744563
 422.03 0.791625

doc/macros.sty

@@ -37,9 +37,7 @@
  		%\toprule
 		\\[-2.2ex]
 		\textbf{Parameter}&\textbf{Type}&\textbf{Description}\\
-		\otoprule
 		#1
-		%\bottomrule
 	\end{tabular}}
 	\end{figure}
 	\setlength\fboxrule\fboxrulebackup
@@ -60,12 +58,8 @@
 \newcommand{\smallrendering}[2]{ \subfigure[#1]{\fbox{\includegraphics[width=0.2\textwidth]{images/#2}}}\hfill}
 
 \newcommand{\parameter}[3]{
-		\small\texttt{#1} & \small #2 & \small #3\\
 		\otoprule
+		\small\texttt{#1} & \small #2 & \small #3 \\
 	}
 
-\newcommand{\lastparameter}[3]{
-		\small\texttt{#1} & \small #2 & \small #3\\
-	}
- 
 \newcommand{\default}[1]{ (Default: #1)}

doc/section_bsdf.tex

@@ -1,4 +1,16 @@
 \subsection{Surface scattering models}
+\begin{figure}[h!]
+\centering
+\includegraphics[width=15.5cm]{images/bsdf_overview.pdf}
+\caption{
+	Schematic overview of the surface scattering models that ship with
+	Mitsuba. The arrows indicate possible outcomes of an
+	interaction with a surface that has the respective model applied to it.
+	\vspace{4mm}
+}
+\end{figure}
+
+
 \label{sec:bsdfs}
 Surface scattering models describe the manner in which light interacts
 with surfaces in the scene. They conveniently summarize the mesoscopic 
@@ -11,53 +23,11 @@ please refer to Sections~\ref{sec:media} and \ref{sec:subsurface}.
 This section presents an overview of all surface scattering models that are 
 supported, along with their parameters.
 
-\subsubsection*{Correctness considerations}
-\begin{figure}[b!]
-\centering
-\vspace{-5mm}
-\includegraphics[width=15cm]{images/glass_explanation.pdf}
-\vspace{-5mm}
-\caption{
-	\label{fig:glass-explanation}
-	Some of the scattering models in Mitsuba need to know
-	the indices of refraction on the exterior and interior-facing
-	side of a surface. 
-	It is therefore important to decompose the mesh into meaningful
-	separate surfaces corresponding to each index of refraction change.
-	The example here shows such a decomposition for a water-filled Glass.
-}
-\end{figure}
-
-
-A vital consideration when modeling a scene in a physically-based rendering 
-system is that the used materials do not violate physical properties, and 
-that their arrangement is meaningful. For instance, imagine having designed
-an architectural interior scene that looks good except for a white desk that 
-seems a bit too dark. A closer inspection reveals that it uses a Lambertian 
-material with a diffuse reflectance of $0.9$. 
-
-In many rendering systems, it would be feasible to increase the 
-reflectance value above $1.0$ in such a situation. But in Mitsuba, even a 
-small surface that reflects a little more light than it receives will 
-likely break the available rendering algorithms, or cause them to produce otherwise 
-unpredictable results. In fact, we should rather change the lighting setup and
-then \emph{reduce} the material's reflectance, since it is quite unlikely that 
-we could find a real-world desk with a reflectance as high as $0.9$.
-
-As an example of the necessity for a meaningful material arrangement, consider
-the glass model illustrated in \figref{glass-explanation}. Here, careful thinking 
-is needed to decompose the object into boundaries that mark index of 
-refraction-changes. If this is done incorrectly and a beam of light can
-potentially pass through a sequence of incompatible index of refraction changes (e.g. $1.00\to 1.33$
-followed by $1.50\to1.33$), the output is undefined and will quite likely
-even contain inaccuracies in parts of the scene that are some distance
-away from the glass.
-
 \subsubsection*{BSDFs}
 To achieve realistic results, Mitsuba comes with a library of both 
 general-purpose surface scattering models (smooth or rough glass, metal,
 plastic, etc.) and specializations to particular materials (woven cloth,
-masks, etc.). Some model plugins fit neither category and could be described
+masks, etc.). Some model plugins fit neither category and can best be described
 as \emph{modifiers} that are applied on top of one or more scattering models. 
 
 Throughout the documentation and within the scene description 
@@ -95,4 +65,45 @@ The following fragment shows an example of both kinds of usages:
 It is generally more economical to use named BSDFs when they
 are used in several places, since this reduces Mitsuba's internal
 memory usage.
+\subsubsection*{Correctness considerations}
+\begin{figure}[b!]
+\centering
+\vspace{-5mm}
+\includegraphics[width=15cm]{images/glass_explanation.pdf}
+\vspace{-5mm}
+\caption{
+	\label{fig:glass-explanation}
+	Some of the scattering models in Mitsuba need to know
+	the indices of refraction on the exterior and interior-facing
+	side of a surface. 
+	It is therefore important to decompose the mesh into meaningful
+	separate surfaces corresponding to each index of refraction change.
+	The example here shows such a decomposition for a water-filled Glass.
+}
+\end{figure}
+
+A vital consideration when modeling a scene in a physically-based rendering 
+system is that the used materials do not violate physical properties, and 
+that their arrangement is meaningful. For instance, imagine having designed
+an architectural interior scene that looks good except for a white desk that 
+seems a bit too dark. A closer inspection reveals that it uses a Lambertian 
+material with a diffuse reflectance of $0.9$. 
+
+In many rendering systems, it would be feasible to increase the 
+reflectance value above $1.0$ in such a situation. But in Mitsuba, even a 
+small surface that reflects a little more light than it receives will 
+likely break the available rendering algorithms, or cause them to produce otherwise 
+unpredictable results. In fact, we should rather change the lighting setup and
+then \emph{reduce} the material's reflectance, since it is quite unlikely that 
+we could find a real-world desk with a reflectance as high as $0.9$.
+
+As an example of the necessity for a meaningful material arrangement, consider
+the glass model illustrated in \figref{glass-explanation}. Here, careful thinking 
+is needed to decompose the object into boundaries that mark index of 
+refraction-changes. If this is done incorrectly and a beam of light can
+potentially pass through a sequence of incompatible index of refraction changes (e.g. $1.00\to 1.33$
+followed by $1.50\to1.33$), the output is undefined and will quite likely
+even contain inaccuracies in parts of the scene that are some distance
+away from the glass.
+
 

include/mitsuba/core/frame.h

@@ -112,6 +112,38 @@ struct Frame {
 		return 1.0f - v.z * v.z;
 	}
 
+	/** \brief Assuming that the given direction is in the local coordinate 
+	 * system, return the sine of the phi parameter in spherical coordinates */
+	inline static Float sinPhi(const Vector &v) {
+		Float sinTheta = Frame::sinTheta(v);
+		if (sinTheta == 0.0f)
+			return 1.0f;
+		return clamp(v.y / sinTheta, -1.0f, 1.0f);
+	}
+
+	/** \brief Assuming that the given direction is in the local coordinate 
+	 * system, return the cosine of the phi parameter in spherical coordinates */
+	inline static Float cosPhi(const Vector &v) {
+		Float sinTheta = Frame::sinTheta(v);
+		if (sinTheta == 0.0f)
+			return 1.0f;
+		return clamp(v.x / sinTheta, -1.0f, 1.0f);
+	}
+
+	/** \brief Assuming that the given direction is in the local coordinate
+	 * system, return the squared sine of the phi parameter in  spherical
+	 * coordinates */
+	inline static Float sinPhiSquared(const Vector &v) {
+		return clamp(v.y * v.y / sinTheta2(v), 0.0f, 1.0f);
+	}
+
+	/** \brief Assuming that the given direction is in the local coordinate
+	 * system, return the squared cosine of the phi parameter in  spherical
+	 * coordinates */
+	inline static Float cosPhiSquared(const Vector &v) {
+		return clamp(v.x * v.x / sinTheta2(v), 0.0f, 1.0f);
+	}
+
 	/// Return a string representation of this frame
 	inline std::string toString() const {
 		std::ostringstream oss;

src/bsdfs/conductor.cpp

@@ -32,7 +32,7 @@ MTS_NAMESPACE_BEGIN
  *     \parameter{k}{\Spectrum}{Imaginary part of the material's index of 
  *             refraction, also known as absorption coefficient.
  *             \default{based on the value of \texttt{material}}}
- *     \lastparameter{specular\showbreak Reflectance}{\Spectrum\Or\Texture}{
+ *     \parameter{specular\showbreak Reflectance}{\Spectrum\Or\Texture}{
  *        Optional factor used to modulate the reflectance component
  *        \default{1.0}}
  * }

src/bsdfs/dielectric.cpp

@@ -31,7 +31,7 @@ MTS_NAMESPACE_BEGIN
  *      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
+ *     \parameter{specular\showbreak Transmittance}{\Spectrum\Or\Texture}{Optional
  *         factor used to modulate the transmittance component\default{1.0}}
  * }
  *

src/bsdfs/difftrans.cpp

@@ -25,7 +25,7 @@ MTS_NAMESPACE_BEGIN
 /*! \plugin{difftrans}{Diffuse transmitter}
  *
  * \parameters{
- *     \lastparameter{transmittance}{\Spectrum\Or\Texture}{
+ *     \parameter{transmittance}{\Spectrum\Or\Texture}{
  *       Specifies the diffuse transmittance of the material
  *       \default{0.5}
  *     }

src/bsdfs/diffuse.cpp

@@ -25,17 +25,20 @@ MTS_NAMESPACE_BEGIN
 /*!\plugin{diffuse}{Smooth diffuse material}
  * \order{1}
  * \parameters{
- *     \lastparameter{reflectance}{\Spectrum\Or\Texture}{
+ *     \parameter{reflectance}{\Spectrum\Or\Texture}{
- *       Specifies the diffuse reflectance / albedo of the material \linebreak(Default: 0.5)
+ *       Specifies the diffuse albedo of the 
+ *       material \default{0.5}
  *     }
  * }
  *
  * \renderings{
- *     \rendering{Homogeneous reflectance, see \lstref{diffuse-uniform}}{bsdf_diffuse_plain}
+ *     \rendering{Homogeneous reflectance, see \lstref{diffuse-uniform}}
- *     \rendering{Textured reflectance, see \lstref{diffuse-textured}}{bsdf_diffuse_textured}
+ *         {bsdf_diffuse_plain}
+ *     \rendering{Textured reflectance, see \lstref{diffuse-textured}}
+ *         {bsdf_diffuse_textured}
  * }
  *
- * The smooth diffuse material (sometimes referred to as ``Lambertian'')
+ * The smooth diffuse material (also referred to as ``Lambertian'')
  * represents an ideally diffuse material with a user-specified amount of 
  * reflectance. Any received illumination is scattered so that the surface 
  * looks the same independently of the direction of observation.
@@ -51,13 +54,15 @@ MTS_NAMESPACE_BEGIN
  * consider using the \pluginref{twosided} BRDF adapter plugin.
  * \vspace{4mm}
  *
- * \begin{xml}[caption={A diffuse material, whose reflectance is specified as an sRGB color}, label=lst:diffuse-uniform]
+ * \begin{xml}[caption={A diffuse material, whose reflectance is specified 
+ *     as an sRGB color}, label=lst:diffuse-uniform]
  * <bsdf type="diffuse">
  *     <srgb name="reflectance" value="#6d7185"/>
  * </bsdf>
  * \end{xml}
  *
- * \begin{xml}[caption=A diffuse material with a texture map, label=lst:diffuse-textured]
+ * \begin{xml}[caption=A diffuse material with a texture map,
+ *     label=lst:diffuse-textured]
  * <bsdf type="diffuse">
  *     <texture type="bitmap" name="reflectance">
  *         <string name="filename" value="wood.jpg"/>

src/bsdfs/plastic.cpp

@@ -31,7 +31,7 @@ MTS_NAMESPACE_BEGIN
  *      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 component\default{1.0}}
- *     \lastparameter{diffuse\showbreak Reflectance}{\Spectrum\Or\Texture}{Optional
+ *     \parameter{diffuse\showbreak Reflectance}{\Spectrum\Or\Texture}{Optional
  *         factor used to modulate the diffuse component\default{0.5}}
  * }
  *

src/bsdfs/roughconductor.cpp

@@ -62,7 +62,7 @@ MTS_NAMESPACE_BEGIN
  *         \default{0.1}. 
  *     }
  *     \parameter{alphaU, alphaV}{\Float\Or\Texture}{
- *         Specifies the anisotropic rougness values along the tangent and 
+ *         Specifies the anisotropic roughness values along the tangent and 
  *         bitangent directions. These parameter are only valid when 
  *         \texttt{distribution=as}. \default{0.1}. 
  *     }
@@ -73,7 +73,7 @@ MTS_NAMESPACE_BEGIN
  *     \parameter{k}{\Spectrum}{Imaginary part of the material's index of 
  *             refraction, also known as absorption coefficient.
  *             \default{based on the value of \texttt{material}}}
- *     \lastparameter{specular\showbreak Reflectance}{\Spectrum\Or\Texture}{Optional
+ *     \parameter{specular\showbreak Reflectance}{\Spectrum\Or\Texture}{Optional
  *         factor used to modulate the reflectance component\default{1.0}}
  * }
  * This plugin implements a realistic microfacet scattering model for rendering
@@ -117,7 +117,7 @@ MTS_NAMESPACE_BEGIN
  * 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 $\alpha=0.3-0.5$ is \emph{extremely} rough (e.g. an etched or ground
+ * and $\alpha=0.3-0.7$ is \emph{extremely} rough (e.g. an etched or ground
  * finish).
  * \vspace{-2mm}
  * \subsubsection*{Techical details}\vspace{-2mm}

src/bsdfs/roughdielectric.cpp

@@ -59,7 +59,7 @@ MTS_NAMESPACE_BEGIN
  *         \default{0.1}. 
  *     }
  *     \parameter{alphaU, alphaV}{\Float\Or\Texture}{
- *         Specifies the anisotropic rougness values along the tangent and 
+ *         Specifies the anisotropic roughness values along the tangent and 
  *         bitangent directions. These parameter are only valid when 
  *         \texttt{distribution=as}. \default{0.1}. 
  *     }
@@ -69,7 +69,7 @@ MTS_NAMESPACE_BEGIN
  *      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
+ *     \parameter{specular\showbreak Transmittance}{\Spectrum\Or\Texture}{Optional
  *         factor used to modulate the transmittance component\default{1.0}}
  * }\vspace{4mm}
  *
@@ -111,7 +111,7 @@ MTS_NAMESPACE_BEGIN
  * 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 $\alpha=0.3-0.5$ is \emph{extremely} rough (e.g. an etched or ground
+ * and $\alpha=0.3-0.7$ is \emph{extremely} rough (e.g. an etched or ground
  * finish).
  * 
  * Please note that when using this plugin, it is crucial that the scene contains
@@ -142,7 +142,7 @@ MTS_NAMESPACE_BEGIN
  * \renderings{
  *     \rendering{Ground glass (GGX, $\alpha$=0.304, 
  *     	   \lstref{roughdielectric-roughglass})}{bsdf_roughdielectric_ggx_0_304.jpg}
- *     \rendering{Textured rougness (\lstref{roughdielectric-textured})}
+ *     \rendering{Textured roughness (\lstref{roughdielectric-textured})}
  *         {bsdf_roughdielectric_textured.jpg}
  * }
  *
@@ -467,7 +467,7 @@ public:
 				      1. Take the Fresnel term with respect to the surface
 					     normal to be a good approximation to the microsurface
 						 Fresnel term -- this will be less true for higher 
-						 rougness values. To be safe, clamp it to some 
+						 roughness values. To be safe, clamp it to some 
 						 reasonable range.
 					  2. Use this approximate term and a random number to
 					     choose between reflection and refraction component.
@@ -595,7 +595,7 @@ public:
 				      1. Take the Fresnel term with respect to the surface
 					     normal to be a good approximation to the microsurface
 						 Fresnel term -- this will be less true for higher 
-						 rougness values. To be safe, clamp it to some 
+						 roughness values. To be safe, clamp it to some 
 						 reasonable range.
 					  2. Use this approximate term and a random number to
 					     choose between reflection and refraction component.

src/bsdfs/roughdiffuse.cpp

@@ -21,60 +21,65 @@
 
 MTS_NAMESPACE_BEGIN
 
-/*!\plugin{diffuse}{Rough diffuse material}
+/*!\plugin{roughdiffuse}{Rough diffuse material}
  * \order{2}
  * \parameters{
  *     \parameter{reflectance}{\Spectrum\Or\Texture}{
- *         Specifies the reflectance / albedo of the material \linebreak(Default: 0.5)
+ *         Specifies the diffuse albedo of the 
+ *         material. \default{0.5}
  *     }
- *     \lastparameter{alpha}{\Spectrum\Or\Texture}{
+ *     \parameter{alpha}{\Spectrum\Or\Texture}{
- *         Specifies the roughness of the unresolved surface microgeometry. 
+ *         Specifies the roughness of the unresolved surface microgeometry
- *         This parameter is approximately equal to the \emph{root mean square} 
+ *         using the \emph{root mean square} (RMS) slope of the 
- *         (RMS) slope of the microfacets.\default{0.1}
+ *         microfacets. \default{0.2}
+ *     }
+ *     \parameter{useFastApprox}{\Boolean}{
+ *         This parameter selects between the full version of the model
+ *         or a fast approximation that still retains most qualitative features.
+ *         \default{\texttt{false}, i.e. use the high-quality version}
  *     }
  * }
  *
  * \renderings{
- *     \rendering{Homogeneous reflectance, see \lstref{diffuse-uniform}}{bsdf_diffuse_plain}
+ *     \rendering{Smooth diffuse surface ($\alpha=0$)}
- *     \rendering{Textured reflectance, see \lstref{diffuse-textured}}{bsdf_diffuse_textured}
+ *        {bsdf_roughdiffuse_0}
+ *     \rendering{Very rough diffuse surface ($\alpha=0.7$)}
+ *        {bsdf_roughdiffuse_0_7}
+ *   \vspace{-3mm}
+ *   \caption{The effect of switching from smooth to rough diffuse scattering 
+ *   is fairly subtle on this model---generally, there will be higher 
+ *   reflectance at grazing angles, as well as an overall reduced contrast.}\vspace{3mm}
  * }
  * 
- * This reflectance model describes scattering from a rough diffuse material,
+ * This reflectance model describes the interaction of light with a rough 
- * such as plaster, sand, clay, or concrete.
+ * diffuse material, such as plaster, sand, clay, or concrete.
  * The underlying theory was developed by Oren and Nayar 
  * \cite{Oren1994Generalization}, who model the microscopic surface structure as 
  * unresolved planar facets arranged in V-shaped grooves, where each facet
  * is an ideal diffuse reflector. The model takes into account shadowing,
  * masking, as well as interreflections between the facets.
  *
- * Since the original publication in 1994, this approach has been shown to 
+ * Since the original publication, this approach has been shown to 
  * be a good match for many real-world materials, particularly compared 
  * to Lambertian scattering, which does not take surface roughness into account.
  *
  * The implementation in Mitsuba uses a surface roughness parameter $\alpha$ that
- * is slighly different from the slope-area variance in the original paper. 
+ * is slighly different from the slope-area variance in the original 1994 paper. 
  * The reason for this change is to make the parameter $\alpha$ portable
- * across different models (i.e. \pluginref{roughglass},
+ * across different models (i.e. \pluginref{roughglass}, \pluginref{roughplastic}, 
  * \pluginref{roughconductor}).
  *
  * To get an intuition about the effect of the 
  * 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 (for such small
- * values, the model will behave almost identically to \pluginref{diffuse}), $\alpha=0.1$ 
+ * values, the model will behave identically to \pluginref{diffuse}), $\alpha=0.1$ 
- * is relatively rough, and $\alpha=0.3-0.5$ is \emph{extremely} rough 
+ * is relatively rough, and $\alpha=0.3-0.7$ is \emph{extremely} rough 
  * (e.g. an etched or ground surface). 
  *
  * 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.
- * \vspace{4mm}
- *
- * \begin{xml}[caption={A diffuse material, whose reflectance is specified as an sRGB color}, label=lst:diffuse-uniform]
- * <bsdf type="diffuse">
- *     <srgb name="reflectance" value="#6d7185"/>
- * </bsdf>
- * \end{xml}
  */
 class RoughDiffuse : public BSDF {
 public:
@@ -84,9 +89,11 @@ public:
 		   'reflectance' and 'diffuseReflectance' as parameter names */
 		m_reflectance = new ConstantSpectrumTexture(props.getSpectrum(
 			props.hasProperty("reflectance") ? "reflectance" 
-				: "diffuseReflectance", Spectrum(.5f)));
+				: "diffuseReflectance", Spectrum(0.5f)));
 
-		m_alpha = new ConstantFloatTexture(props.getFloat("alpha", 0.1f));
+		m_useFastApprox = props.getBoolean("useFastApprox", false);
+
+		m_alpha = new ConstantFloatTexture(props.getFloat("alpha", 0.2f));
 		m_components.push_back(EGlossyReflection | EFrontSide);
 		m_usesRayDifferentials = false;
 	}
@@ -95,6 +102,7 @@ public:
 		: BSDF(stream, manager) {
 		m_reflectance = static_cast<Texture *>(manager->getInstance(stream));
 		m_alpha = static_cast<Texture *>(manager->getInstance(stream));
+		m_useFastApprox = stream->readBool();
 		m_components.push_back(EGlossyReflection | EFrontSide);
 		m_usesRayDifferentials = m_reflectance->usesRayDifferentials();
 	}
@@ -110,7 +118,7 @@ public:
 
 	Spectrum eval(const BSDFQueryRecord &bRec, EMeasure measure) const {
 		if (!(bRec.typeMask & EGlossyReflection) || measure != ESolidAngle
-			|| Frame::cosTheta(bRec.wi) <= 0 
+			|| Frame::cosTheta(bRec.wi) <= 0
 			|| Frame::cosTheta(bRec.wo) <= 0)
 			return Spectrum(0.0f);
 
@@ -124,12 +132,80 @@ public:
 		Float sigma = m_alpha->getValue(bRec.its).average() 
 			* conversionFactor;
 
-		Float sigma2 = sigma*sigma;
+		const Float sigma2 = sigma*sigma;
-		Float A = 10.f - (sigma2 / (2.0f * (sigma2 + 0.33f)));
-		Float B = 0.45f * sigma2 / (sigma2 + 0.09f);
 
-		return m_reflectance->getValue(bRec.its)
+		Float sinThetaI = Frame::sinTheta(bRec.wi),
-			* (INV_PI * Frame::cosTheta(bRec.wo));
+			  sinThetaO = Frame::sinTheta(bRec.wo);
+
+		Float cosPhiDiff = 0;
+		if (sinThetaI > Epsilon && sinThetaO > Epsilon) {
+			/* Compute cos(phiO-phiI) using the half-angle formulae */
+			Float sinPhiI = Frame::sinPhi(bRec.wi),
+				  cosPhiI = Frame::cosPhi(bRec.wi),
+				  sinPhiO = Frame::sinPhi(bRec.wo),
+				  cosPhiO = Frame::cosPhi(bRec.wo);
+			cosPhiDiff = cosPhiI * cosPhiO + sinPhiI * sinPhiO;
+		}
+
+		if (m_useFastApprox) {
+			Float A = 1.0f - 0.5f * sigma2 / (sigma2 + 0.33f),
+				  B = 0.45f * sigma2 / (sigma2 + 0.09f),
+				  sinAlpha, tanBeta;
+	
+			if (Frame::cosTheta(bRec.wi) > Frame::cosTheta(bRec.wo)) {
+				sinAlpha = sinThetaO;
+				tanBeta = sinThetaI / Frame::cosTheta(bRec.wi);
+			} else {
+				sinAlpha = sinThetaI;
+				tanBeta = sinThetaO / Frame::cosTheta(bRec.wo);
+			}
+	
+			return m_reflectance->getValue(bRec.its)
+				* (INV_PI * Frame::cosTheta(bRec.wo) * (A + B
+				* std::max(cosPhiDiff, (Float) 0.0f) * sinAlpha * tanBeta));
+		} else {
+			Float sinThetaI = Frame::sinTheta(bRec.wi),
+				  sinThetaO = Frame::sinTheta(bRec.wo),
+				  thetaI = std::acos(Frame::cosTheta(bRec.wi)),
+				  thetaO = std::acos(Frame::cosTheta(bRec.wo)),
+				  alpha = std::max(thetaI, thetaO),
+				  beta = std::min(thetaI, thetaO);
+	
+			Float sinAlpha, sinBeta, tanBeta;
+			if (Frame::cosTheta(bRec.wi) > Frame::cosTheta(bRec.wo)) {
+				sinAlpha = sinThetaO; sinBeta = sinThetaI;
+				tanBeta = sinThetaI / Frame::cosTheta(bRec.wi);
+			} else {
+				sinAlpha = sinThetaI; sinBeta = sinThetaO;
+				tanBeta = sinThetaO / Frame::cosTheta(bRec.wo);
+			}
+	
+			Float tmp = sigma2 / (sigma2 + 0.09f),
+				  tmp2 = (4*INV_PI*INV_PI) * alpha * beta,
+				  tmp3 = 2*beta*INV_PI;
+	
+			Float C1 = 1.0f - 0.5f * sigma2 / (sigma2 + 0.33f),
+				  C2 = 0.45f * tmp,
+				  C3 = 0.125f * tmp * tmp2 * tmp2,
+				  C4 = 0.17f * sigma2 / (sigma2 + 0.13f);
+	
+			if (cosPhiDiff > 0)
+				C2 *= sinAlpha;
+			else
+				C2 *= sinAlpha - tmp3*tmp3*tmp3;
+	
+			/* Compute tan(0.5 * (alpha+beta)) using the half-angle formulae */
+			Float tanHalf = (sinAlpha + sinBeta) / (
+					std::sqrt(std::max((Float) 0.0f, 1.0f - sinAlpha * sinAlpha)) +
+					std::sqrt(std::max((Float) 0.0f, 1.0f - sinBeta  * sinBeta)));
+	
+			Spectrum rho = m_reflectance->getValue(bRec.its),
+					 snglScat = rho * (C1 + cosPhiDiff * C2 * tanBeta +
+					    (1.0f - std::abs(cosPhiDiff)) * C3 * tanHalf),
+					 dblScat = rho * rho * (C4 * (1.0f - cosPhiDiff*tmp3*tmp3));
+	
+			return  (snglScat + dblScat) * (INV_PI * Frame::cosTheta(bRec.wo));
+		}
 	}
 
 	Float pdf(const BSDFQueryRecord &bRec, EMeasure measure) const {
@@ -148,7 +224,8 @@ public:
 		bRec.wo = squareToHemispherePSA(sample);
 		bRec.sampledComponent = 0;
 		bRec.sampledType = EGlossyReflection;
-		return m_reflectance->getValue(bRec.its);
+		return eval(bRec, ESolidAngle) /
+			(Frame::cosTheta(bRec.wo) * INV_PI);
 	}
 
 	Spectrum sample(BSDFQueryRecord &bRec, Float &pdf, const Point2 &sample) const {
@@ -159,8 +236,7 @@ public:
 		bRec.sampledComponent = 0;
 		bRec.sampledType = EGlossyReflection;
 		pdf = Frame::cosTheta(bRec.wo) * INV_PI;
-		return m_reflectance->getValue(bRec.its) 
+		return eval(bRec, ESolidAngle);
-			* (INV_PI * Frame::cosTheta(bRec.wo));
 	}
 
 	void addChild(const std::string &name, ConfigurableObject *child) {
@@ -182,6 +258,7 @@ public:
 
 		manager->serialize(stream, m_reflectance.get());
 		manager->serialize(stream, m_alpha.get());
+		stream->writeBool(m_useFastApprox);
 	}
 
 	std::string toString() const {
@@ -189,7 +266,8 @@ public:
 		oss << "RoughDiffuse[" << endl
 			<< "  name = \"" << getName() << "\"," << endl
 			<< "  reflectance = " << indent(m_reflectance->toString()) << "," << endl
-			<< "  alpha = " << indent(m_alpha->toString()) << endl
+			<< "  alpha = " << indent(m_alpha->toString()) << "," << endl
+			<< "  useFastApprox = " << m_useFastApprox << endl
 			<< "]";
 		return oss.str();
 	}
@@ -200,6 +278,7 @@ public:
 private:
 	ref<Texture> m_reflectance;
 	ref<Texture> m_alpha;
+	bool m_useFastApprox;
 };
 
 // ================ Hardware shader implementation ================ 
@@ -233,11 +312,27 @@ public:
 		oss << "vec3 " << evalName << "(vec2 uv, vec3 wi, vec3 wo) {" << endl
 			<< "    if (cosTheta(wi) < 0.0 || cosTheta(wo) < 0.0)" << endl
 			<< "    	return vec3(0.0);" << endl
-			<< "    return " << depNames[0] << "(uv) * 0.31831 * cosTheta(wo);" << endl
+			<< "    float sigma = " << depNames[1] << "(uv)[0] * 0.70711;" << endl
+			<< "    float sigma2 = sigma * sigma;" << endl
+			<< "    float A = 1.0 - 0.5 * sigma2 / (sigma2 + 0.33);" << endl
+			<< "    float B = 0.45 * sigma2 / (sigma2 + 0.09);" << endl
+			<< "    float maxCos = max(0.0, cosPhi(wi)*cosPhi(wo)+sinPhi(wi)*sinPhi(wo));" << endl
+			<< "    float sinAlpha, tanBeta;" << endl
+			<< "    if (cosTheta(wi) > cosTheta(wo)) {" << endl
+			<< "        sinAlpha = sinTheta(wo);" << endl
+			<< "        tanBeta = sinTheta(wi) / cosTheta(wi);" << endl
+			<< "    } else {" << endl
+			<< "        sinAlpha = sinTheta(wi);" << endl
+			<< "        tanBeta = sinTheta(wo) / cosTheta(wo);" << endl
+			<< "    }" << endl
+			<< "    float value = A + B * maxCos * sinAlpha * tanBeta;" << endl
+			<< "    return " << depNames[0] << "(uv) * 0.31831 * cosTheta(wo) * value;" << endl
 			<< "}" << endl
 			<< endl
 			<< "vec3 " << evalName << "_diffuse(vec2 uv, vec3 wi, vec3 wo) {" << endl
-			<< "    return " << evalName << "(uv, wi, wo);" << endl
+			<< "    if (cosTheta(wi) < 0.0 || cosTheta(wo) < 0.0)" << endl
+			<< "    	return vec3(0.0);" << endl
+			<< "    return " << depNames[0] << "(uv) * 0.31831 * cosTheta(wo);" << endl
 			<< "}" << endl;
 	}
 

src/converter/collada.cpp

@@ -1103,7 +1103,7 @@ void loadCamera(ColladaContext &ctx, Transform transform, domCamera &camera) {
 	int xres=768;
 
 	// Cameras in Mitsuba point along the positive Z axis (COLLADA: neg. Z)
-	transform = transform * Transform::scale(Vector(1,1,-1));
+	transform = transform * Transform::scale(Vector(1, 1, -1));
 
 	std::ostringstream matrix;
 	for (int i=0; i<4; ++i)
@@ -1130,14 +1130,8 @@ void loadCamera(ColladaContext &ctx, Transform transform, domCamera &camera) {
 			xres = ctx.cvt->m_xres;
 			aspect = (Float) ctx.cvt->m_xres / (Float) ctx.cvt->m_yres;
 		} else {
-			if (persp->getAspect_ratio().cast() != 0) {
+			if (persp->getAspect_ratio().cast() != 0)
 				aspect = (Float) persp->getAspect_ratio()->getValue();
-				if (std::abs(aspect-0.1) < Epsilon) {
-					SLog(EWarn, "Found the suspicious aspect ratio \"0.1\", which is likely due to a bug in Blender 2.5"
-						" - setting to 1.0. Please use the \"-r\" parameter to override the resolution.");
-					aspect = 1.0f;
-				}
-			}
 		}
 		ctx.os << "\t<camera id=\"" << identifier << "\" type=\"perspective\">" << endl;
 		if (persp->getXfov().cast()) {

src/libcore/transform.cpp

@@ -174,16 +174,16 @@ Transform Transform::glOrthographic(Float clipNear, Float clipFar) {
 Transform Transform::lookAt(const Point &p, const Point &t, const Vector &up) {
 	Matrix4x4 result;
 
-	Vector dirct = normalize(t-p);
+	Vector dir = normalize(t-p);
-	Vector right = normalize(cross(dirct, up));
+	Vector left = normalize(cross(normalize(up), dir));
 
 	/* Generate a new, orthogonalized up vector */
-	Vector newUp = cross(right, dirct);
+	Vector newUp = cross(dir, left);
 
 	/* Store as columns */
-	result.m[0][0] = right.x; result.m[1][0] = right.y; result.m[2][0] = right.z; result.m[3][0] = 0;
+	result.m[0][0] = left.x;  result.m[1][0] = left.y;  result.m[2][0] = left.z;  result.m[3][0] = 0;
 	result.m[0][1] = newUp.x; result.m[1][1] = newUp.y; result.m[2][1] = newUp.z; result.m[3][1] = 0;
-	result.m[0][2] = dirct.x; result.m[1][2] = dirct.y; result.m[2][2] = dirct.z; result.m[3][2] = 0;
+	result.m[0][2] = dir.x;   result.m[1][2] = dir.y;   result.m[2][2] = dir.z;   result.m[3][2] = 0;
 	result.m[0][3] = p.x;     result.m[1][3] = p.y;     result.m[2][3] = p.z;     result.m[3][3] = 1;
 
 	return Transform(result);

src/libhw/vpl.cpp

@@ -308,6 +308,7 @@ void VPLShaderManager::setVPL(const VPL &vpl) {
 				case 4: lightViewTrafo = Transform::lookAt(p, p + Vector(0, 0, 1), Vector(0, 1, 0)).inverse(); break;
 				case 5: lightViewTrafo = Transform::lookAt(p, p + Vector(0, 0, -1), Vector(0, 1, 0)).inverse(); break;
 			}
+			lightViewTrafo = Transform::scale(Vector(-1, 1, 1)) * lightViewTrafo;
 			const Matrix4x4 &viewMatrix = lightViewTrafo.getMatrix();
 			m_shadowProgram->setParameter(m_shadowProgramParam_cubeMapTransform[i], lightProjTrafo * lightViewTrafo);
 			m_shadowProgram->setParameter(m_shadowProgramParam_depthVec[i], Vector4(
@@ -331,6 +332,7 @@ void VPLShaderManager::setVPL(const VPL &vpl) {
 				case 4: lightViewTrafo = Transform::lookAt(p, p + Vector(0, 0, 1), Vector(0, 1, 0)).inverse(); break;
 				case 5: lightViewTrafo = Transform::lookAt(p, p + Vector(0, 0, -1), Vector(0, 1, 0)).inverse(); break;
 			}
+			lightViewTrafo = Transform::scale(Vector(-1, 1, 1)) * lightViewTrafo;
 			const Matrix4x4 &viewMatrix = lightViewTrafo.getMatrix();
 
 			m_altShadowProgram->setParameter(m_altShadowProgramParam_cubeMapTransform, lightProjTrafo * lightViewTrafo);
@@ -368,13 +370,6 @@ void VPLShaderManager::configure(const VPL &vpl, const BSDF *bsdf,
 		return;
 	}
 
-#if 0
-	if (bsdfShader->getFlags() & Shader::ETransparent) {
-		m_renderer->setColor(Spectrum(1.0f), 0.3f);
-		return;
-	}
-#endif
-
 	bool anisotropic = bsdf->getType() & BSDF::EAnisotropic;
 
 	m_targetConfig = VPLProgramConfiguration(vplShader, bsdfShader, 
@@ -495,6 +490,8 @@ void VPLShaderManager::configure(const VPL &vpl, const BSDF *bsdf,
 			<< "float sinTheta2(vec3 v) { return 1.0-v.z*v.z; }" << endl
 			<< "float sinTheta(vec3 v) { float st2 = sinTheta2(v); if (st2 <= 0) return 0.0; else return sqrt(sinTheta2(v)); }" << endl
 			<< "float tanTheta(vec3 v) { return sinTheta(v)/cosTheta(v); }" << endl
+			<< "float sinPhi(vec3 v) { return v.y/sinTheta(v); }" << endl
+			<< "float cosPhi(vec3 v) { return v.x/sinTheta(v); }" << endl
 			<< endl;
 
 		std::string vplEvalName, bsdfEvalName, lumEvalName;

src/librender/scene.cpp

@@ -237,14 +237,17 @@ void Scene::configure() {
 			Float maxExtents = std::max(extents.x, extents.y);
 			Float distance = maxExtents/(2.0f * std::tan(45 * .5f * M_PI/180));
 
-			props.setTransform("toWorld", Transform::translate(Vector(center.x, center.y, aabb.min.z - distance)));
+			props.setTransform("toWorld", Transform::translate(Vector(center.x, 
+					center.y, aabb.min.z - distance)));
 			props.setFloat("fov", 45.0f);
 
-			m_camera = static_cast<Camera *> (PluginManager::getInstance()->createObject(MTS_CLASS(Camera), props));
+			m_camera = static_cast<Camera *> (PluginManager::getInstance()->
+					createObject(MTS_CLASS(Camera), props));
 			m_camera->configure();
 			m_sampler = m_camera->getSampler();
 		} else {
-			Log(EWarn, "Unable to set up a default camera -- does the scene contain anything at all?");
+			Log(EWarn, "Unable to set up a default camera -- does the scene "
+				"contain anything at all?");
 		}
 	}
 

src/qtgui/glwidget.cpp

@@ -675,7 +675,7 @@ void GLWidget::mouseMoveEvent(QMouseEvent *event) {
 			if (coords.x < 0 || coords.x > M_PI) 
 				m_context->up *= -1;
 
-			if (camera->getViewTransform().det3x3() < 0) 
+			if (camera->getViewTransform().det3x3() > 0) 
 				camera->setInverseViewTransform(Transform::lookAt(p, target, m_context->up));
 			else
 				camera->setInverseViewTransform(
@@ -693,7 +693,7 @@ void GLWidget::mouseMoveEvent(QMouseEvent *event) {
 					* camera->getViewTransform();
 			d = trafo.inverse()(Vector(0,0,1));
 
-			if (camera->getViewTransform().det3x3() < 0) 
+			if (camera->getViewTransform().det3x3() > 0) 
 				camera->setInverseViewTransform(Transform::lookAt(p, p+d, up));
 			else
 				camera->setInverseViewTransform(
@@ -713,7 +713,7 @@ void GLWidget::mouseMoveEvent(QMouseEvent *event) {
 			Float roll = rel.x() * m_mouseSensitivity * .02f;
 			Float fovChange = rel.y() * m_mouseSensitivity * .03f;
 
-			if (camera->getViewTransform().det3x3() < 0) {
+			if (camera->getViewTransform().det3x3() > 0) {
 				m_context->up = Transform::rotate(d, roll)(up);
 				camera->setInverseViewTransform(Transform::lookAt(p, p+d, m_context->up));
 			} else {
@@ -743,7 +743,7 @@ void GLWidget::mouseMoveEvent(QMouseEvent *event) {
 			Vector d = Vector(camera->getImagePlaneNormal());
 			p = p + (oldFocusDepth - focusDepth) * d;
 
-			if (camera->getViewTransform().det3x3() < 0) 
+			if (camera->getViewTransform().det3x3() > 0) 
 				camera->setInverseViewTransform(Transform::lookAt(p, p+d, up));
 			else
 				camera->setInverseViewTransform(
@@ -809,8 +809,13 @@ void GLWidget::wheelEvent(QWheelEvent *event) {
 		Vector d = Vector(camera->getImagePlaneNormal());
 		Point o = camera->getPosition() + (oldFocusDepth - focusDepth) * d;
 
-		camera->setInverseViewTransform(
+		if (camera->getViewTransform().det3x3() > 0) 
-				Transform::lookAt(o, o+d, up));
+			camera->setInverseViewTransform(Transform::lookAt(o, o+d, up));
+		else
+			camera->setInverseViewTransform(
+				Transform::lookAt(o, o+d, up) *
+				Transform::scale(Vector(-1,1,1))
+			);
 
 		m_wheelTimer->reset();
 		if (!m_movementTimer->isActive())

src/qtgui/save.cpp

@@ -165,7 +165,7 @@ void saveScene(QWidget *parent, SceneContext *ctx, const QString &targetFile) {
 		   u = ctx->up;
 	Point t, p = sceneCamera->getInverseViewTransform()(Point(0,0,0));
 
-	if (sceneCamera->getViewTransform().det3x3() > 0) {
+	if (sceneCamera->getViewTransform().det3x3() < 0) {
 		QDomElement scale = doc.createElement("scale");
 		scale.setAttribute("x", "-1");
 		cameraTransform.insertBefore(scale, lookAt);