rough coating documentation

data/tests/test_bsdf.xml

@@ -1,18 +1,7 @@
 <!-- This file defines a series of BSDF instances
 	 to be tested for consistency. This is done
 	 using the testcase 'test_chisquare' -->
-<scene version="0.3.0">
-	<bsdf type="roughcoating">
-		<!--
-		<bsdf type="roughconductor">
-			<string name="distribution" value="beckmann"/>
-			<float name="alpha" value=".3"/>
-		</bsdf>
-		-->
-		<bsdf type="diffuse"/>
-		<float name="alpha" value=".3"/>
-	</bsdf>
-
+<scene version="0.3.0">	
 	<!-- Test the smooth diffuse model -->
 	<bsdf type="diffuse"/>
 
@@ -211,4 +200,12 @@
 			<float name="thickness" value="2"/>
 		</bsdf>
 	</bsdf>
+
+	<!-- Test the rough coating model -->
+	<bsdf type="roughcoating">
+		<bsdf type="roughconductor">
+			<string name="distribution" value="beckmann"/>
+			<float name="alpha" value=".3"/>
+		</bsdf>
+	</bsdf>
 </scene>

doc/main.tex

@@ -138,9 +138,12 @@
 % ----- 8< ----- 8< ------
 
 \title{
-	\includegraphics[width=4cm]{images/logo_plain.pdf}\\\vspace{2cm}
-	Mitsuba Documentation\\\vspace{3mm}
-	\large Version \MitsubaVersion
+	\vspace{3cm}
+	\includegraphics[width=4cm]{images/logo_plain.pdf}\\\vspace{1.5cm}
+	\Huge
+	Mitsuba Documentation\\\vspace{4mm}
+	\LARGE Version \MitsubaVersion
+	\vspace{5mm}
 }
 \author{Wenzel Jakob}
 \date{\today}

src/bsdfs/coating.cpp

@@ -48,9 +48,9 @@ MTS_NAMESPACE_BEGIN
  *
  * This plugin implements a smooth dielectric coating (e.g. a layer of varnish) 
  * in the style of the paper ``Arbitrarily Layered Micro-Facet Surfaces'' by 
- * Weidlich and Wilkie \cite{Weidlich2007Arbitrarily}. Any non-transmissive
- * BSDF in Mitsuba can be coated using this plugin, and multiple coating layers
- * can be applied in sequence. This allows designing interesting custom materials 
+ * Weidlich and Wilkie \cite{Weidlich2007Arbitrarily}. Any BSDF in Mitsuba 
+ * can be coated using this plugin, and multiple coating layers can even 
+ * be applied in sequence. This allows designing interesting custom materials 
  * like car paint or glazed metal foil. The coating layer can optionally be 
  * tinted (i.e. filled with an absorbing medium), in which case this model also 
  * accounts for the directionally dependent absorption within the layer.

src/bsdfs/roughcoating.cpp

@@ -25,7 +25,7 @@ MTS_NAMESPACE_BEGIN
 
 #define TRANSMITTANCE_PRECOMP_NODES 200
 
-/*!\plugin{roughcoating}{Rough coating material}
+/*!\plugin{roughcoating}{Rough dielectric coating}
  * \order{10}
  * \icon{bsdf_roughcoating}
  * \parameters{
@@ -59,8 +59,37 @@ MTS_NAMESPACE_BEGIN
  *     \parameter{sigmaA}{\Spectrum\Or\Texture}{The absorption coefficient of the 
  *      coating layer. \default{0, i.e. there is no absorption}}
  *     \parameter{\Unnamed}{\BSDF}{A nested BSDF model that should be coated.}
+ * }\vspace{-4mm}
+ * \renderings{
+ *     \rendering{Rough gold coated with a \emph{smooth} varnish layer}
+ *         {bsdf_roughcoating_gold_smooth}
+ *     \rendering{Rough gold coated with a \emph{rough} ($\alpha\!=\!0.03$) varnish layer}
+ *         {bsdf_roughcoating_gold_rough}
  * }
  *
+ * This plugin implements a \emph{very} approximate\footnote{
+ * The model only accounts for roughness 
+ * in the specular reflection and Fresnel transmittance through the interface.
+ * The interior model receives incident illumination
+ * that is transformed \emph{as if} the coating was smooth. While
+ * that's not quite correct, it is a convenient workaround when the 
+ * \pluginref{coating} plugin produces specular highlights that are too sharp.}
+ * model that simulates a rough dielectric coating. It is essentially the 
+ * roughened version of \pluginref{coating}. 
+ * Any BSDF in Mitsuba can be coated using this plugin, and multiple coating 
+ * layers can even be applied in sequence. This allows designing interesting 
+ * custom materials. The coating layer can optionally be tinted (i.e. filled 
+ * with an absorbing medium), in which case this model also accounts for the 
+ * directionally dependent absorption within the layer.
+*
+ * Note that the plugin discards illumination that undergoes internal
+ * reflection within the coating. This can lead to a noticeable energy
+ * loss for materials that reflect much of their energy near or below the critical
+ * angle (i.e. diffuse or very rough materials). 
+ *
+ * The implementation here is influenced by the paper 
+ * ``Arbitrarily Layered Micro-Facet Surfaces'' by Weidlich and 
+ * Wilkie \cite{Weidlich2007Arbitrarily}.
  */
 class RoughCoating : public BSDF {
 public: