new <default> XML tag, which creates a default value for a parameter that has not been specified on the command line

data/schema/scene.xsd

@@ -28,6 +28,7 @@
 				<xsd:element name="blackbody" type="blackbody"/>
 
 				<xsd:element name="alias" type="alias"/>
+				<xsd:element name="default" type="string"/>
 			</xsd:choice>
 			<xsd:attribute name="version" type="xsd:string"/>
 		</xsd:complexType>
@@ -49,6 +50,7 @@
 			<xsd:element name="rgb" type="rgb"/>
 			<xsd:element name="srgb" type="string"/>
 			<xsd:element name="blackbody" type="blackbody"/>
+			<xsd:element name="default" type="string"/>
 		</xsd:choice>
 	</xsd:group>
 

doc/format.tex

@@ -368,13 +368,28 @@ This lets you include different parts of a scene configuration by changing the c
 \begin{xml}
 <include filename="nested-scene-$\texttt{\$}$version.xml"/>
 \end{xml}
+\subsection{Default parameter values}
+As mentioned before, scenes may contain named parameters that are supplied via the command line:
+\begin{xml}
+<bsdf type="diffuse">
+    <rgb name="reflectance" value="$\texttt{\$}$reflectance"/>
+</bsdf>
+\end{xml}
+In this case, an error will occur when loading the scene without an explicit command line argument of the form
+\code{-Dreflectance=}\mbox{$\langle$\emph{something}$\rangle$}. For convenience, it is possible to specify
+a default parameter value that takes precedence when no command line arguments are given. The syntax for this is
+\begin{xml}
+<default name="reflectance" value="something"/>
+\end{xml}
+and must precede occurrences of the parameter in the XML file.
+
 \subsection{Aliases}
 Sometimes, it can be useful to associate an object (e.g. a scattering model)
 with multiple identifiers. This can be accomplished using the \code{alias
 as=..} keyword:
 \begin{xml}
-	<bsdf type="diffuse" id="myMaterial1"/>
+<bsdf type="diffuse" id="myMaterial1"/>
-	<alias id="myMaterial1" as="myMaterial2"/>
+<alias id="myMaterial1" as="myMaterial2"/>
 \end{xml}
 After this statement, the diffuse scattering model will be bound to
 \emph{both} identifiers ``\code{myMaterial1}'' and ``\code{myMaterial2}''.

include/mitsuba/render/scenehandler.h

@@ -158,7 +158,7 @@ private:
 		ELookAt, EScale, EMatrix, EPoint,
 		EVector, ERGB, ESRGB, EBlackBody,
 		ESpectrum, ETransform, EAnimation,
-		EInclude, EAlias
+		EInclude, EAlias, EDefault
 	};
 
 	typedef std::pair<ETag, const Class *> TagEntry;

src/libcore/quad.cpp

@@ -195,7 +195,7 @@ void gaussLegendre(int n, Float *nodes, Float *weights) {
 
 		while (true) {
 			if (++it > 20)
-				SLog(EError, "gaussLegendre(): did not converge after 20 iterations!");
+				SLog(EError, "gaussLegendre(%i): did not converge after 20 iterations!", n);
 
 			/* Search for the interior roots of P_{n+1}(x) using Newton's method. */
 			std::pair<double, double> L = legendrePD(n+1, x);
@@ -219,7 +219,6 @@ void gaussLegendre(int n, Float *nodes, Float *weights) {
 	}
 }
 
-
 void gaussLobatto(int n, Float *nodes, Float *weights) {
 	if (n-- < 2)
 		SLog(EError, "gaussLobatto(): n must be >= 2");
@@ -238,7 +237,7 @@ void gaussLobatto(int n, Float *nodes, Float *weights) {
 
 		while (true) {
 			if (++it > 20)
-				SLog(EError, "gaussLobatto(): did not converge after 20 iterations!");
+				SLog(EError, "gaussLobatto(%i): did not converge after 20 iterations!", n);
 
 			/* Search for the interior roots of P_n'(x) using Newton's method. The same
 			   roots are also shared by P_{n+1}-P_{n-1}, which is nicer to evaluate. */

src/librender/scenehandler.cpp

@@ -102,9 +102,10 @@ SceneHandler::SceneHandler(const SAXParser *parser,
 	m_tags["blackbody"]  = TagEntry(EBlackBody,  (Class *) NULL);
 	m_tags["spectrum"]   = TagEntry(ESpectrum,   (Class *) NULL);
 	m_tags["transform"]  = TagEntry(ETransform,  (Class *) NULL);
-	m_tags["animation"]  = TagEntry(EAnimation, (Class *) NULL);
+	m_tags["animation"]  = TagEntry(EAnimation,  (Class *) NULL);
 	m_tags["include"]    = TagEntry(EInclude,    (Class *) NULL);
 	m_tags["alias"]      = TagEntry(EAlias,      (Class *) NULL);
+	m_tags["default"]    = TagEntry(EDefault,    (Class *) NULL);
 
 	XMLTransService::Codes failReason;
 	m_transcoder = XMLPlatformUtils::fgTransService->makeNewTranscoderFor(
@@ -656,6 +657,12 @@ void SceneHandler::endElement(const XMLCh* const xmlName) {
 			}
 			break;
 
+		case EDefault: {
+				if (m_params.find(context.attributes["name"]) == m_params.end())
+					m_params[context.attributes["name"]] = context.attributes["value"];
+			}
+			break;
+
 		default: {
 				if (tag.second == NULL)
 					XMLLog(EError, "Internal error: could not instantiate an object "