added an optional feature to hide directly visible light sources -- this is convenient for making paper figures etc. where one don't want the environment map to 'bleed' into the foreground objects (see the committed images for an example)

doc/section_integrators.tex

@@ -112,4 +112,25 @@ Some of the rendering techniques in Mitsuba are \emph{progressive}.
 What this means is that they display a rough preview, which improves over time.
 Leaving them running indefinitely will continually reduce noise (in unbiased algorithms
 such as Metropolis Light Transport) or noise and bias (in biased
-rendering techniques such as Progressive Photon Mapping).
+ endering techniques such as Progressive Photon Mapping).
+\newpage
+\subsubsection*{Hiding directly visible emitters}
+\label{sec:hideemitters}
+Several rendering algorithms in Mitsuba have a feature to hide directly
+visible light sources (e.g. environment maps or area lights). While not
+particularly realistic, this feature is often convenient to remove a background
+from a rendering so that it can be pasted into a differently-colored document.
+
+Note that only directly visible emitters can be hidden using this feature---a
+reflection on a shiny surface will be unaffected. To perform the kind of
+compositing shown in Figure~\ref{fig:hideemitters}, it is also necessary to
+enable the alpha channel in the scene's film instance (Section~\ref{sec:films}).
+
+\renderings{
+  \unframedrendering{Daylit smoke rendered with \code{hideEmitters} set to \code{false}
+     (the default setting)}{integrator_volpath_normal}
+     \unframedrendering{Rendered with \code{hideEmitters} set to \code{true} and alpha-composited
+      onto a white background.}{integrator_volpath_hideemitters}
+      \caption{\label{fig:hideemitters}An example application of the \code{hideEmitters} parameter
+    together with alpha blending}
+}

include/mitsuba/render/integrator.h

@@ -458,6 +458,7 @@ protected:
     int m_maxDepth;
     int m_rrDepth;
 	bool m_strictNormals;
+	bool m_hideEmitters;
 };
 
 MTS_NAMESPACE_END

src/integrators/direct/direct.cpp

@@ -25,20 +25,29 @@ MTS_NAMESPACE_BEGIN
  * \parameters{
  *     \parameter{shadingSamples}{\Integer}{This convenience parameter can be
  *         used to set both \code{emitterSamples} and \code{bsdfSamples} at
- *         the same time.}
+ *         the same time.
+ *     }
  *     \parameter{emitterSamples}{\Integer}{Optional more fine-grained
  *        parameter: specifies the number of samples that should be generated
  *        using the direct illumination strategies implemented by the scene's
- *        emitters\default{set to the value of \code{shadingSamples}}}
+ *        emitters\default{set to the value of \code{shadingSamples}}
+ *     }
  *     \parameter{bsdfSamples}{\Integer}{Optional more fine-grained
  *        parameter: specifies the number of samples that should be generated
  *        using the BSDF sampling strategies implemented by the scene's
- *        surfaces\default{set to the value of \code{shadingSamples}}}
+ *        surfaces\default{set to the value of \code{shadingSamples}}
+ *     }
  *     \parameter{strictNormals}{\Boolean}{Be strict about potential
- *        inconsistencies involving shading normals? See \pluginref{path}
+ *        inconsistencies involving shading normals? See
- *        for details.\default{no, i.e. \code{false}}}
+ *        page~\pageref{sec:strictnormals} for details.
+ *        \default{no, i.e. \code{false}}
+ *     }
+ *     \parameter{hideEmitters}{\Boolean}{Hide directly visible emitters?
+ *        See page~\pageref{sec:hideemitters} for details.
+ *        \default{no, i.e. \code{false}}
+ *     }
  * }
- *
+ * \vspace{-1mm}
  * \renderings{
  *     \medrendering{Only BSDF sampling}{integrator_direct_bsdf}
  *     \medrendering{Only emitter sampling}{integrator_direct_lum}
@@ -92,6 +101,9 @@ public:
 		m_bsdfSamples = props.getSize("bsdfSamples", shadingSamples);
 		/* Be strict about potential inconsistencies involving shading normals? */
 		m_strictNormals = props.getBoolean("strictNormals", false);
+		/* When this flag is set to true, contributions from directly
+		 * visible emitters will not be included in the rendered image */
+		m_hideEmitters = props.getBoolean("hideEmitters", false);
 		Assert(m_emitterSamples + m_bsdfSamples > 0);
 	}
 
@@ -101,6 +113,7 @@ public:
 		m_emitterSamples = stream->readSize();
 		m_bsdfSamples = stream->readSize();
 		m_strictNormals = stream->readBool();
+		m_hideEmitters = stream->readBool();
 		configure();
 	}
 
@@ -109,6 +122,7 @@ public:
 		stream->writeSize(m_emitterSamples);
 		stream->writeSize(m_bsdfSamples);
 		stream->writeBool(m_strictNormals);
+		stream->writeBool(m_hideEmitters);
 	}
 
 	void configure() {
@@ -142,14 +156,14 @@ public:
 		if (!rRec.rayIntersect(ray)) {
 			/* If no intersection could be found, possibly return
 			   radiance from a background emitter */
-			if (rRec.type & RadianceQueryRecord::EEmittedRadiance)
+			if (rRec.type & RadianceQueryRecord::EEmittedRadiance && !m_hideEmitters)
 				return scene->evalEnvironment(ray);
 			else
 				return Spectrum(0.0f);
 		}
 
 		/* Possibly include emitted radiance if requested */
-		if (its.isEmitter() && (rRec.type & RadianceQueryRecord::EEmittedRadiance))
+		if (its.isEmitter() && (rRec.type & RadianceQueryRecord::EEmittedRadiance) && !m_hideEmitters)
 			Li += its.Le(-ray.d);
 
 		/* Include radiance from a subsurface scattering model if requested */
@@ -271,7 +285,7 @@ public:
 				/* Intersected nothing -- perhaps there is an environment map? */
 				const Emitter *env = scene->getEnvironmentEmitter();
 
-				if (!env)
+				if (!env || (m_hideEmitters && bRec.sampledType == BSDF::ENull))
 					continue;
 
 				value = env->evalEnvironment(RayDifferential(bsdfRay));
@@ -316,6 +330,7 @@ private:
 	Float m_fracBSDF, m_fracLum;
 	Float m_weightBSDF, m_weightLum;
 	bool m_strictNormals;
+	bool m_hideEmitters;
 };
 
 MTS_IMPLEMENT_CLASS_S(MIDirectIntegrator, false, SamplingIntegrator)

src/integrators/path/path.cpp

@@ -38,7 +38,12 @@ static StatsCounter avgPathLength("Path tracer", "Average path length", EAverage
  *	   }
  *     \parameter{strictNormals}{\Boolean}{Be strict about potential
  *        inconsistencies involving shading normals? See the description below
- *        for details.\default{no, i.e. \code{false}}}
+ *        for details.\default{no, i.e. \code{false}}
+ *     }
+ *     \parameter{hideEmitters}{\Boolean}{Hide directly visible emitters?
+ *        See page~\pageref{sec:hideemitters} for details.
+ *        \default{no, i.e. \code{false}}
+ *     }
  * }
  *
  * This integrator implements a basic path tracer and is a \emph{good default choice}
@@ -75,7 +80,8 @@ static StatsCounter avgPathLength("Path tracer", "Average path length", EAverage
  * low-discrepancy sample generators (i.e. \pluginref{ldsampler},
  * \pluginref{halton}, or \pluginref{sobol}).
  *
- * \paragraph{Strict normals:} Triangle meshes often rely on interpolated shading normals
+ * \paragraph{Strict normals:}\label{sec:strictnormals}
+ * Triangle meshes often rely on interpolated shading normals
  * to suppress the inherently faceted appearance of the underlying geometry. These
  * ``fake'' normals are not without problems, however. They can lead to paradoxical
  * situations where a light ray impinges on an object from a direction that is classified as ``outside''
@@ -116,6 +122,7 @@ public:
 		Intersection &its = rRec.its;
 		RayDifferential ray(r);
 		Spectrum Li(0.0f);
+		bool scattered = false;
 
 		/* Perform the first ray intersection (or ignore if the
 		   intersection has already been provided). */
@@ -129,7 +136,8 @@ public:
 			if (!its.isValid()) {
 				/* If no intersection could be found, potentially return
 				   radiance from a environment luminaire if it exists */
-				if (rRec.type & RadianceQueryRecord::EEmittedRadiance)
+				if ((rRec.type & RadianceQueryRecord::EEmittedRadiance)
+					&& (!m_hideEmitters || scattered))
 					Li += throughput * scene->evalEnvironment(ray);
 				break;
 			}
@@ -137,7 +145,8 @@ public:
 			const BSDF *bsdf = its.getBSDF(ray);
 
 			/* Possibly include emitted radiance if requested */
-			if (its.isEmitter() && (rRec.type & RadianceQueryRecord::EEmittedRadiance))
+			if (its.isEmitter() && (rRec.type & RadianceQueryRecord::EEmittedRadiance)
+				&& (!m_hideEmitters || scattered))
 				Li += throughput * its.Le(-ray.d);
 
 			/* Include radiance from a subsurface scattering model if requested */
@@ -201,6 +210,8 @@ public:
 			if (bsdfWeight.isZero())
 				break;
 
+			scattered |= bRec.sampledType != BSDF::ENull;
+
 			/* Prevent light leaks due to the use of shading normals */
 			const Vector wo = its.toWorld(bRec.wo);
 			Float woDotGeoN = dot(its.geoFrame.n, wo);
@@ -224,6 +235,9 @@ public:
 				const Emitter *env = scene->getEnvironmentEmitter();
 
 				if (env) {
+					if (m_hideEmitters && !scattered)
+						break;
+
 					value = env->evalEnvironment(ray);
 					if (!env->fillDirectSamplingRecord(dRec, ray))
 						break;

src/integrators/path/volpath.cpp

@@ -37,8 +37,14 @@ static StatsCounter avgPathLength("Volumetric path tracer", "Average path length
  *	      path termination criterion. \default{\code{5}}
  *	   }
  *     \parameter{strictNormals}{\Boolean}{Be strict about potential
- *        inconsistencies involving shading normals? See \pluginref{path}
+ *        inconsistencies involving shading normals? See
- *        for details.\default{no, i.e. \code{false}}}
+ *        page~\pageref{sec:strictnormals} for details.
+ *        \default{no, i.e. \code{false}}
+ *     }
+ *     \parameter{hideEmitters}{\Boolean}{Hide directly visible emitters?
+ *        See page~\pageref{sec:hideemitters} for details.
+ *        \default{no, i.e. \code{false}}
+ *     }
  * }
  *
  * This plugin provides a volumetric path tracer that can be used to
@@ -151,7 +157,6 @@ public:
 					break;
 				throughput *= phaseVal;
 
-
 				/* Trace a ray in this direction */
 				ray = Ray(mRec.p, pRec.wo, ray.time);
 				ray.mint = 0;
@@ -186,7 +191,8 @@ public:
 				if (!its.isValid()) {
 					/* If no intersection could be found, possibly return
 					   attenuated radiance from a background luminaire */
-					if (rRec.type & RadianceQueryRecord::EEmittedRadiance) {
+					if ((rRec.type & RadianceQueryRecord::EEmittedRadiance)
+						&& (!m_hideEmitters || scattered)) {
 						Spectrum value = throughput * scene->evalEnvironment(ray);
 						if (rRec.medium)
 							value *= rRec.medium->evalTransmittance(ray);
@@ -197,7 +203,8 @@ public:
 				}
 
 				/* Possibly include emitted radiance if requested */
-				if (its.isEmitter() && (rRec.type & RadianceQueryRecord::EEmittedRadiance))
+				if (its.isEmitter() && (rRec.type & RadianceQueryRecord::EEmittedRadiance)
+					&& (!m_hideEmitters || scattered))
 					Li += throughput * its.Le(-ray.d);
 
 				/* Include radiance from a subsurface integrator if requested */

src/integrators/path/volpath_simple.cpp

@@ -37,8 +37,14 @@ static StatsCounter avgPathLength("Volumetric path tracer", "Average path length
  *	      path termination criterion. \default{\code{5}}
  *	   }
  *     \parameter{strictNormals}{\Boolean}{Be strict about potential
- *        inconsistencies involving shading normals? See \pluginref{path}
+ *        inconsistencies involving shading normals? See
- *        for details.\default{no, i.e. \code{false}}}
+ *        page~\pageref{sec:strictnormals} for details.
+ *        \default{no, i.e. \code{false}}
+ *     }
+ *     \parameter{hideEmitters}{\Boolean}{Hide directly visible emitters?
+ *        See page~\pageref{sec:hideemitters} for details.
+ *        \default{no, i.e. \code{false}}
+ *     }
  * }
  *
  * This plugin provides a basic volumetric path tracer that can be used to
@@ -86,7 +92,7 @@ public:
 		MediumSamplingRecord mRec;
 		RayDifferential ray(r);
 		Spectrum Li(0.0f);
-		bool nullChain = true;
+		bool nullChain = true, scattered = false;
 		Float eta = 1.0f;
 
 		/* Perform the first ray intersection (or ignore if the
@@ -153,6 +159,7 @@ public:
 				ray.mint = 0;
 				scene->rayIntersect(ray, its);
 				nullChain = false;
+				scattered = true;
 			} else {
 				/* Sample
 					tau(x, y) * (Surface integral). This happens with probability mRec.pdfFailure
@@ -165,7 +172,8 @@ public:
 				if (!its.isValid()) {
 					/* If no intersection could be found, possibly return
 					   attenuated radiance from a background luminaire */
-					if (rRec.type & RadianceQueryRecord::EEmittedRadiance) {
+					if ((rRec.type & RadianceQueryRecord::EEmittedRadiance)
+						&& (!m_hideEmitters || scattered)) {
 						Spectrum value = throughput * scene->evalEnvironment(ray);
 						if (rRec.medium)
 							value *= rRec.medium->evalTransmittance(ray);
@@ -175,7 +183,8 @@ public:
 				}
 
 				/* Possibly include emitted radiance if requested */
-				if (its.isEmitter() && (rRec.type & RadianceQueryRecord::EEmittedRadiance))
+				if (its.isEmitter() && (rRec.type & RadianceQueryRecord::EEmittedRadiance)
+					&& (!m_hideEmitters || scattered))
 					Li += throughput * its.Le(-ray.d);
 
 				/* Include radiance from a subsurface integrator if requested */
@@ -267,6 +276,7 @@ public:
 				/* In the next iteration, trace a ray in this direction */
 				ray = Ray(its.p, wo, ray.time);
 				scene->rayIntersect(ray, its);
+				scattered |= bRec.sampledType != BSDF::ENull;
 			}
 
 			if (rRec.depth++ >= m_rrDepth) {

src/integrators/photonmapper/photonmapper.cpp

@@ -46,6 +46,10 @@ MTS_NAMESPACE_BEGIN
  *		Granularity of photon tracing work units for the purpose
  *		of parallelization (in \# of shot particles) \default{0, i.e. decide automatically}
  *     }
+ *     \parameter{hideEmitters}{\Boolean}{Hide directly visible emitters?
+ *        See page~\pageref{sec:hideemitters} for details.
+ *        \default{no, i.e. \code{false}}
+ *     }
  *	   \parameter{rrDepth}{\Integer}{Specifies the minimum path depth, after
  *	      which the implementation will start to use the ``russian roulette''
  *	      path termination criterion. \default{\code{5}}
@@ -126,6 +130,9 @@ public:
 		m_gatherLocally = props.getBoolean("gatherLocally", true);
 		/* Indicates if the gathering steps should be canceled if not enough photons are generated. */
 		m_autoCancelGathering = props.getBoolean("autoCancelGathering", true);
+		/* When this flag is set to true, contributions from directly
+		 * visible emitters will not be included in the rendered image */
+		m_hideEmitters = props.getBoolean("hideEmitters", false);
 
 		if (m_maxDepth == 0) {
 			Log(EError, "maxDepth must be greater than zero!");
@@ -159,6 +166,7 @@ public:
 		m_volumeLookupSize = stream->readInt();
 		m_gatherLocally = stream->readBool();
 		m_autoCancelGathering = stream->readBool();
+		m_hideEmitters = stream->readBool();
 		m_causticPhotonMapID = m_globalPhotonMapID = m_breID = 0;
 		configure();
 	}
@@ -190,6 +198,7 @@ public:
 		stream->writeInt(m_volumeLookupSize);
 		stream->writeBool(m_gatherLocally);
 		stream->writeBool(m_autoCancelGathering);
+		stream->writeBool(m_hideEmitters);
 	}
 
 	/// Configure the sampler for a specified amount of direct illumination samples
@@ -261,11 +270,11 @@ public:
 			if (proc->getReturnStatus() != ParallelProcess::ESuccess)
 				return false;
 
-			Log(EDebug, "Global photon map full. Shot " SIZE_T_FMT " particles, excess photons due to parallelism: "
-				SIZE_T_FMT, proc->getShotParticles(), proc->getExcessPhotons());
-
 			ref<PhotonMap> globalPhotonMap = proc->getPhotonMap();
 			if (globalPhotonMap->isFull()) {
+				Log(EDebug, "Global photon map full. Shot " SIZE_T_FMT " particles, excess photons due to parallelism: "
+					SIZE_T_FMT, proc->getShotParticles(), proc->getExcessPhotons());
+
 				m_globalPhotonMap = globalPhotonMap;
 				m_globalPhotonMap->setScaleFactor(1 / (Float) proc->getShotParticles());
 				m_globalPhotonMap->build();
@@ -292,11 +301,11 @@ public:
 			if (proc->getReturnStatus() != ParallelProcess::ESuccess)
 				return false;
 
-			Log(EDebug, "Caustic photon map full. Shot " SIZE_T_FMT " particles, excess photons due to parallelism: "
-				SIZE_T_FMT, proc->getShotParticles(), proc->getExcessPhotons());
-
 			ref<PhotonMap> causticPhotonMap = proc->getPhotonMap();
 			if (causticPhotonMap->isFull()) {
+				Log(EDebug, "Caustic photon map full. Shot " SIZE_T_FMT " particles, excess photons due to parallelism: "
+					SIZE_T_FMT, proc->getShotParticles(), proc->getExcessPhotons());
+
 				m_causticPhotonMap = causticPhotonMap;
 				m_causticPhotonMap->setScaleFactor(1 / (Float) proc->getShotParticles());
 				m_causticPhotonMap->build();
@@ -324,11 +333,11 @@ public:
 			if (proc->getReturnStatus() != ParallelProcess::ESuccess)
 				return false;
 
-			Log(EDebug, "Volume photon map full. Shot " SIZE_T_FMT " particles, excess photons due to parallelism: "
-				SIZE_T_FMT, proc->getShotParticles(), proc->getExcessPhotons());
-
 			ref<PhotonMap> volumePhotonMap = proc->getPhotonMap();
 			if (volumePhotonMap->isFull()) {
+				Log(EDebug, "Volume photon map full. Shot " SIZE_T_FMT " particles, excess photons due to parallelism: "
+					SIZE_T_FMT, proc->getShotParticles(), proc->getExcessPhotons());
+
 				volumePhotonMap->setScaleFactor(1 / (Float) proc->getShotParticles());
 				volumePhotonMap->build();
 				m_bre = new BeamRadianceEstimator(volumePhotonMap, m_volumeLookupSize);
@@ -407,13 +416,13 @@ public:
 		if (!its.isValid()) {
 			/* If no intersection could be found, possibly return
 			   attenuated radiance from a background luminaire */
-			if (rRec.type & RadianceQueryRecord::EEmittedRadiance)
+			if ((rRec.type & RadianceQueryRecord::EEmittedRadiance) && !m_hideEmitters)
 				LiSurf = scene->evalEnvironment(ray);
 			return LiSurf * transmittance + LiMedium;
 		}
 
 		/* Possibly include emitted radiance if requested */
-		if (its.isEmitter() && (rRec.type & RadianceQueryRecord::EEmittedRadiance))
+		if (its.isEmitter() && (rRec.type & RadianceQueryRecord::EEmittedRadiance) && !m_hideEmitters)
 			LiSurf += its.Le(-ray.d);
 
 		/* Include radiance from a subsurface scattering model if requested */
@@ -446,7 +455,7 @@ public:
 				RadianceQueryRecord rRec2;
 				for (int i=0; i<compCount; i++) {
 					unsigned int type = bsdf->getType(i);
-					if (!(type & BSDF::EDelta) && type == BSDF::ENull)
+					if (!(type & BSDF::EDelta))
 						continue;
 					/* Sample the BSDF and recurse */
 					BSDFSamplingRecord bRec(its, rRec.sampler, ERadiance);
@@ -676,6 +685,7 @@ private:
 	int m_granularity, m_directSamples, m_glossySamples;
 	int m_rrDepth, m_maxDepth, m_maxSpecularDepth;
 	bool m_gatherLocally, m_autoCancelGathering;
+	bool m_hideEmitters;
 };
 
 MTS_IMPLEMENT_CLASS_S(PhotonMapIntegrator, false, SamplingIntegrator)

src/librender/integrator.cpp

@@ -211,6 +211,12 @@ MonteCarloIntegrator::MonteCarloIntegrator(const Properties &props) : SamplingIn
 	 */
 	m_strictNormals = props.getBoolean("strictNormals", false);
 
+	/**
+	 * When this flag is set to true, contributions from directly
+	 * visible emitters will not be included in the rendered image
+	 */
+	m_hideEmitters = props.getBoolean("hideEmitters", false);
+
 	if (m_rrDepth <= 0)
 		Log(EError, "'rrDepth' must be set to a value greater than zero!");
 
@@ -223,6 +229,7 @@ MonteCarloIntegrator::MonteCarloIntegrator(Stream *stream, InstanceManager *mana
 	m_rrDepth = stream->readInt();
 	m_maxDepth = stream->readInt();
 	m_strictNormals = stream->readBool();
+	m_hideEmitters = stream->readBool();
 }
 
 void MonteCarloIntegrator::serialize(Stream *stream, InstanceManager *manager) const {
@@ -230,6 +237,7 @@ void MonteCarloIntegrator::serialize(Stream *stream, InstanceManager *manager) c
 	stream->writeInt(m_rrDepth);
 	stream->writeInt(m_maxDepth);
 	stream->writeBool(m_strictNormals);
+	stream->writeBool(m_hideEmitters);
 }
 
 std::string RadianceQueryRecord::toString() const {

src/mtsgui/resources/docs.xml

@@ -41,6 +41,10 @@
 			implicitly have <tt>strictNormals</tt> activated. Hence, another use of this parameter
 			is to match renderings created by these methods.</p>
 		</param>
+		<param name="hideEmitters" readableName="Hide directly visible emitters" type="boolean" default="false" importance="1">
+			Hide light sources (e.g. area or environment light sources) that are directly visible to the camera?
+			Reflections of light sources remain unaffected.
+		</param>
 	</plugin>
 
 	<plugin type="integrator" name="irrcache" readableName="Irradiance cache"
@@ -191,6 +195,10 @@
 			implicitly have <tt>strictNormals</tt> activated. Hence, another use of this parameter
 			is to match renderings created by these methods.</p>
 		</param>
+		<param name="hideEmitters" readableName="Hide directly visible emitters" type="boolean" default="false" importance="1">
+			Hide light sources (e.g. area or environment light sources) that are directly visible to the camera?
+			Reflections of light sources remain unaffected.
+		</param>
 	</plugin>
 
 	<plugin type="integrator" name="path" readableName="Path tracer"
@@ -350,6 +358,10 @@
 			Specifies the minimum path depth, after which the implementation will start to use the
 			"russian roulette" path termination criterion when tracing photons (set to <tt>-1</tt> to disable).
 		</param>
+		<param name="hideEmitters" readableName="Hide directly visible emitters" type="boolean" default="false" importance="1">
+			Hide light sources (e.g. area or environment light sources) that are directly visible to the camera?
+			Reflections of light sources remain unaffected.
+		</param>
 	</plugin>
 
 	<plugin type="integrator" name="ppm" readableName="Progressive photon mapper"