BSDFs now flag spatially varying components

data/tests/test_bsdf.xml

@@ -6,6 +6,8 @@
 	<bsdf type="coating">
 		<float name="intIOR" value="1.5"/>
 		<float name="extIOR" value="1"/>
+		<rgb name="sigmaA" value="0.1 0.2 0.3"/>
+		<float name="thickness" value="2"/>
 		<bsdf type="diffuse"/>
 	</bsdf>
 

include/mitsuba/hw/basicshader.h

@@ -55,6 +55,10 @@ public:
 		return m_value;
 	}
 
+	inline bool isConstant() const {
+		return true;
+	}
+
 	inline std::string toString() const {
 		std::ostringstream oss;
 		oss << "ConstantSpectrumTexture[value=" << m_value.toString() << "]";
@@ -99,6 +103,10 @@ public:
 		return Spectrum(m_value);
 	}
 
+	inline bool isConstant() const {
+		return true;
+	}
+
 	inline std::string toString() const {
 		std::ostringstream oss;
 		oss << "ConstantFloatTexture[value=" << m_value << "]";

include/mitsuba/render/bsdf.h

@@ -225,10 +225,12 @@ public:
 		// =============================================================
 		/// The lobe is not invariant to rotation around the normal
 		EAnisotropic          = 0x01000,
+		/// The BSDF depends on the UV coordinates
+		ESpatiallyVarying     = 0x02000,
 		/// Supports interactions on the front-facing side
-		EFrontSide            = 0x02000,
+		EFrontSide            = 0x04000,
 		/// Supports interactions on the back-facing side
-		EBackSide             = 0x04000,
+		EBackSide             = 0x08000,
 		/// Can use an extra sampler instance to improve the sampling method
 		ECanUseSampler        = 0x10000  
 		//! @}
@@ -276,7 +278,7 @@ public:
 	inline unsigned int getType(int component) const {
 		return m_components[component];
 	}
-	
+
 	/**
 	 * \brief Return the measure corresponding to a particular
 	 * component type

include/mitsuba/render/texture.h

@@ -43,6 +43,9 @@ public:
 	/// Return the resolution in pixels, if applicable
 	virtual Vector3i getResolution() const;
 
+	/// Return whether the texture takes on a single constant value
+	virtual bool isConstant() const = 0;
+
 	/**
 	 * \brief Does this texture do pre-filtering when ray 
 	 * differentials are available?

src/bsdfs/coating.cpp

@@ -30,37 +30,44 @@ MTS_NAMESPACE_BEGIN
  *      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{sigmaA}{\Spectrum\Or\Texture}{Absorption coefficient within the layer. \default{0}}
+ *     \parameter{thickness}{\Float}{Denotes the thickness of the absorbing layer (given in inverse units of \code{sigmaA})\default{1}}
- *     \parameter{thickness}{\Float}{Thickness of the absorbing layer (given in inverse units of \code{sigmaA})\default{1}}
+ *     \parameter{sigmaA}{\Spectrum\Or\Texture}{The absorption coefficient of the coating layer. \default{0, i.e. there is no absorption}}
  * }
  * 
  * \renderings{
- *     \rendering{Coated rough copper (lower exposure, \lstref{coating-roughcopper})}
+ *     \rendering{Rough copper}
+ *         {bsdf_roughconductor_copper}
+ *     \rendering{The same material coated with a single layer of clear varnish (see \lstref{coating-roughcopper})}
  *         {bsdf_coating_roughconductor}
- *     \rendering{Coated rough plastic}
- *         {bsdf_coating_roughplastic}
  * }
  *
- * This plugin implements a smooth dielectric coating in the style of the
+ * This plugin implements a smooth dielectric coating (e.g. a layer of varnish) 
- * paper ``Arbitrarily Layered Micro-Facet Surfaces'' by Weidlich and 
+ * in the style of the paper ``Arbitrarily Layered Micro-Facet Surfaces'' by 
- * Wilkie \cite{Weidlich2007Arbitrarily}. Any non-transmissive model can
+ * Weidlich and Wilkie \cite{Weidlich2007Arbitrarily}. Any non-transmissive
- * be coated, and multiple layers can be applied in sequence. This allows
+ * BSDF in Mitsuba can be coated using this plugin, and multiple coating layers
- * designing custom materials like car paint.
+ * can 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.
  *
- * The coating layer can optionally be filled with an absorbing medium, 
+ * Note that the plugin discards illumination that undergoes internal
- * in which case this model also accounts for the directionally dependent
+ * reflection within the coating. This can lead to a noticeable energy
- * extinction within the layer.
+ * loss for materials that reflect much of their energy near or below the critical
+ * angle (i.e. diffuse or very rough materials). 
+ * Therefore, users are discouraged to use this plugin to coat smooth
+ * diffuse materials, since there is a separately available plugin
+ * named \pluginref{smoothplastic}, which covers the same case and does not
+ * suffer from energy loss.
  *
  * Evaluating the internal component of this model entails refracting the 
  * incident and exitant rays through the dielectric interface, followed by
  * querying the nested material with this modified direction pair. The result 
- * is attenuated by the two Fresnel transmittances. Note that this model does
+ * is attenuated by the two Fresnel transmittances and the absorption, if any.
- * not attempt to handle illumination that is reflected by the interior of the 
- * coating---this energy is essentially lost.
  *
  * \vspace{4mm}
  *
- * \begin{xml}[caption=Rough copper coated with a transparent layer of lacquer, label=lst:coating-roughcopper]
+ * \begin{xml}[caption=Rough copper coated with a transparent layer of 
+ *     varnish, label=lst:coating-roughcopper]
  * <bsdf type="coating">
  *     <float name="intIOR" value="1.7"/>
  *     <bsdf type="roughconductor">
@@ -79,13 +86,13 @@ public:
 
 		/* Specifies the external index of refraction at the interface */
 		m_extIOR = lookupIOR(props, "extIOR", "air");
-		
-		/* Specifies the absorption within the layer */
-		m_sigmaA = new ConstantSpectrumTexture(
-			props.getSpectrum("sigmaA", Spectrum(0.0f)));
 
 		/* Specifies the layer's thickness using the inverse units of sigmaA */
 		m_thickness = props.getFloat("thickness", 1);
+
+		/* Specifies the absorption within the layer */
+		m_sigmaA = new ConstantSpectrumTexture(
+			props.getSpectrum("sigmaA", Spectrum(0.0f)));
 	}
 
 	SmoothCoating(Stream *stream, InstanceManager *manager) 
@@ -105,11 +112,26 @@ public:
 			Log(EError, "Tried to put a smooth coating layer on top of a BSDF "
 				"with a transmission component -- this is currently not allowed!");
 
+#if COMPENSATE
+		if (m_nested->getClass()->getName() == "SmoothDiffuse") {
+			/* For an ideally diffuse material, it is known how much 
+			   energy will be lost to total internal reflection */
+			m_compensation = (m_intIOR*m_intIOR) / (m_extIOR * m_extIOR);
+		} else {
+			/* Otherwise, give up (for now) */
+			m_compensation = 1.0f;
+		}
+#endif
+		unsigned int extraFlags = 0;
+		if (!m_sigmaA->isConstant())
+			extraFlags |= ESpatiallyVarying;
+
 		m_components.clear();
 		for (int i=0; i<m_nested->getComponentCount(); ++i) 
-			m_components.push_back(m_nested->getType(i));
+			m_components.push_back(m_nested->getType(i) | extraFlags);
+
 		m_components.push_back(EDeltaReflection | EFrontSide);
-		
+
 		m_usesRayDifferentials = m_nested->usesRayDifferentials()
 			|| m_sigmaA->usesRayDifferentials();
 
@@ -206,9 +228,10 @@ public:
 			if (R12 == 1 || R21 == 1) /* Total internal reflection */
 				return Spectrum(0.0f);
 
+			Float eta = m_extIOR / m_intIOR;
 			Spectrum result = m_nested->eval(bRec2, measure)
-				* ((1-R12) * (1-R21));
+				* ((1-R12) * (1-R21) * eta * eta);
-			
+
 			Spectrum sigmaA = m_sigmaA->getValue(bRec.its) * m_thickness;
 			if (!sigmaA.isZero()) 
 				result *= (-sigmaA *
@@ -216,10 +239,12 @@ public:
 					 1/std::abs(Frame::cosTheta(bRec2.wo)))).exp();
 
 			if (measure == ESolidAngle)
-				result *= Frame::cosTheta(bRec2.wo);
+				result *= Frame::cosTheta(bRec.wo)
+					    / Frame::cosTheta(bRec2.wo);
 
-			Float eta = m_extIOR / m_intIOR;
+#ifdef COMPENSATE
-			result *= eta * eta;
+			result *= m_compensation;
+#endif
 
 			return result;
 		}
@@ -250,9 +275,11 @@ public:
 			if (R12 == 1 || R21 == 1) /* Total internal reflection */
 				return 0.0f;
 		
-			Float pdf = m_nested->pdf(bRec2, measure)
+			Float pdf = m_nested->pdf(bRec2, measure);
-				* Frame::cosTheta(bRec.wo)
+
-				/ Frame::cosTheta(bRec2.wo);
+			if (measure == ESolidAngle)
+				pdf *= Frame::cosTheta(bRec.wo)
+					 / Frame::cosTheta(bRec2.wo);
 
 			Float eta = m_extIOR / m_intIOR;
 			pdf *= eta * eta;
@@ -324,11 +351,16 @@ public:
 
 			if (R21 == 1.0f) /* Total internal reflection */
 				return Spectrum(0.0f);
+			bool sampledSA = (BSDF::getMeasure(bRec.sampledType) == ESolidAngle);
+			Float cosRatio = Frame::cosTheta(bRec.wo) / cosThetaWoPrime,
+				  commonTerms = (sampledSA ? cosRatio : 1.0f)* eta * eta;
 
-			pdf *= (sampleSpecular ? (1 - R12) : 1.0f) * eta * eta *
+			pdf *= (sampleSpecular ? (1 - R12) : 1.0f) * commonTerms;
-				Frame::cosTheta(bRec.wo) / cosThetaWoPrime;
+			result *= (1 - R12) * (1 - R21) * commonTerms;
 
-			result *= (1 - R12) * (1 - R21) * cosThetaWoPrime * eta * eta;
+#ifdef COMPENSATE
+			result *= m_compensation;
+#endif
 
 			return result;
 		}
@@ -358,11 +390,14 @@ public:
 	}
 
 	MTS_DECLARE_CLASS()
-private:
+protected:
 	Float m_intIOR, m_extIOR;
 	ref<Texture> m_sigmaA;
 	ref<BSDF> m_nested;
 	Float m_thickness;
+#ifdef COMPENSATE
+	Float m_compensation;
+#endif
 };
 
 MTS_IMPLEMENT_CLASS_S(SmoothCoating, false, BSDF)

src/bsdfs/conductor.cpp

@@ -181,8 +181,9 @@ public:
 			m_specularReflectance->usesRayDifferentials();
 
 		m_components.clear();
-		m_components.push_back(EDeltaReflection | EFrontSide);
+		m_components.push_back(EDeltaReflection | EFrontSide
-		
+			| (m_specularReflectance->isConstant() ? 0 : ESpatiallyVarying));
+
 		BSDF::configure();
 	}
 

src/bsdfs/dielectric.cpp

@@ -176,8 +176,10 @@ public:
 			m_specularTransmittance, "specularTransmittance", 1.0f);
 		
 		m_components.clear();
-		m_components.push_back(EDeltaReflection | EFrontSide | EBackSide);
+		m_components.push_back(EDeltaReflection | EFrontSide | EBackSide
-		m_components.push_back(EDeltaTransmission | EFrontSide | EBackSide);
+			| (m_specularReflectance->isConstant() ? 0 : ESpatiallyVarying));
+		m_components.push_back(EDeltaTransmission | EFrontSide | EBackSide
+			| (m_specularTransmittance->isConstant() ? 0 : ESpatiallyVarying));
 		
 		m_usesRayDifferentials = 
 			m_specularReflectance->usesRayDifferentials() ||

src/bsdfs/difftrans.cpp

@@ -64,7 +64,8 @@ public:
 		m_transmittance = ensureEnergyConservation(m_transmittance, "transmittance", 1.0f);
 
 		m_components.clear();
-		m_components.push_back(EDiffuseTransmission | EFrontSide | EBackSide);
+		m_components.push_back(EDiffuseTransmission | EFrontSide | EBackSide
+			| (m_transmittance->isConstant() ? 0 : ESpatiallyVarying));
 		BSDF::configure();
 	}
 

src/bsdfs/diffuse.cpp

@@ -93,7 +93,8 @@ public:
 		m_reflectance = ensureEnergyConservation(m_reflectance, "reflectance", 1.0f);
 
 		m_components.clear();
-		m_components.push_back(EDiffuseReflection | EFrontSide);
+		m_components.push_back(EDiffuseReflection | EFrontSide
+			| (m_reflectance->isConstant() ? 0 : ESpatiallyVarying));
 		m_usesRayDifferentials = m_reflectance->usesRayDifferentials();
 
 		BSDF::configure();

src/bsdfs/irawan.cpp

@@ -122,8 +122,10 @@ public:
 
 	void configure() {
 		m_components.clear();
-		m_components.push_back(EGlossyReflection | EAnisotropic | EFrontSide);
+		m_components.push_back(EGlossyReflection | EFrontSide
-		m_components.push_back(EDiffuseReflection | EFrontSide);
+			| EAnisotropic | ESpatiallyVarying);
+		m_components.push_back(EDiffuseReflection | EFrontSide
+			| ESpatiallyVarying);
 		BSDF::configure();
 	}
 

src/bsdfs/mask.cpp

@@ -83,10 +83,17 @@ public:
 	void configure() {
 		if (!m_nestedBSDF)
 			Log(EError, "A child BSDF is required");
+		
+		unsigned int extraFlags = 0;
+		if (!m_opacity->isConstant())
+			extraFlags |= ESpatiallyVarying;
+
 		m_components.clear();
 		for (int i=0; i<m_nestedBSDF->getComponentCount(); ++i)
-			m_components.push_back(m_nestedBSDF->getType(i));
+			m_components.push_back(m_nestedBSDF->getType(i) | extraFlags);
-		m_components.push_back(EDeltaTransmission | EFrontSide | EBackSide);
+		m_components.push_back(EDeltaTransmission | EFrontSide 
+				| EBackSide | extraFlags);
+
 		m_usesRayDifferentials = m_nestedBSDF->usesRayDifferentials();
 		m_opacity = ensureEnergyConservation(m_opacity, "opacity", 1.0f);
 		BSDF::configure();

src/bsdfs/mixture.cpp

@@ -28,8 +28,8 @@ MTS_NAMESPACE_BEGIN
  *     \parameter{weights}{\String}{A comma-separated list of BSDF weights}
  * }
  * \renderings{
- *     \rendering{An exemplary combination of BSDFs 
+ *     \rendering{An admittedly not particularly realistic linear combination of
- *     (\lstref{mixture-example})}{bsdf_mixture_test}
+ *     diffuse and specular BSDFs (\lstref{mixture-example})}{bsdf_mixture_test}
  * }
  *
  * This plugin implements a ``mixture'' material, which represents  

src/bsdfs/phong.cpp

@@ -77,8 +77,11 @@ public:
 
 	void configure() {
 		m_components.clear();
-		m_components.push_back(EGlossyReflection | EFrontSide);
+		m_components.push_back(EGlossyReflection | EFrontSide |
-		m_components.push_back(EDiffuseReflection | EFrontSide);
+			((!m_specularReflectance->isConstant()
+			  || !m_exponent->isConstant()) ? ESpatiallyVarying : 0));
+		m_components.push_back(EDiffuseReflection | EFrontSide
+			| (m_diffuseReflectance->isConstant() ? 0 : ESpatiallyVarying));
 
 		/* Verify the input parameters and fix them if necessary */
 		std::pair<Texture *, Texture *> result = ensureEnergyConservation(
@@ -230,7 +233,7 @@ public:
 	}
 
 	Spectrum sample(BSDFQueryRecord &bRec, const Point2 &sample) const {
-		Float pdf;
+		Float pdf = 0;
 		Spectrum result = Phong::sample(bRec, pdf, sample);
 
 		if (result.isZero())

src/bsdfs/plastic.cpp

@@ -103,8 +103,10 @@ public:
 			m_diffuseReflectance->usesRayDifferentials();
 		
 		m_components.clear();
-		m_components.push_back(EDeltaReflection | EFrontSide);
+		m_components.push_back(EDeltaReflection | EFrontSide
-		m_components.push_back(EDiffuseReflection | EFrontSide);
+			| (m_specularReflectance->isConstant() ? 0 : ESpatiallyVarying));
+		m_components.push_back(EDiffuseReflection | EFrontSide
+			| (m_diffuseReflectance->isConstant() ? 0 : ESpatiallyVarying));
 		
 		BSDF::configure();
 	}

src/bsdfs/roughconductor.cpp

@@ -205,10 +205,12 @@ public:
 						"anisotropic Ashikhmin-Shirley microfacet distribution "
 						"(named \"as\")");
 		}
+		if (!m_alphaU->isConstant() || !m_alphaV->isConstant() ||
+			!m_specularReflectance->isConstant())
+			extraFlags |= ESpatiallyVarying;
 
 		m_components.clear();
-		m_components.push_back(
+		m_components.push_back(EGlossyReflection | EFrontSide | extraFlags);
-			EGlossyReflection | EFrontSide | extraFlags);
 
 		/* Verify the input parameters and fix them if necessary */
 		m_specularReflectance = ensureEnergyConservation(

src/bsdfs/roughdielectric.cpp

@@ -227,11 +227,16 @@ public:
 						"(named \"as\")");
 		}
 
+		if (!m_alphaU->isConstant() || !m_alphaV->isConstant())
+			extraFlags |= ESpatiallyVarying;
+
 		m_components.clear();
-		m_components.push_back(
+		m_components.push_back(EGlossyReflection | EFrontSide
-			EGlossyReflection | EFrontSide | EBackSide | ECanUseSampler | extraFlags);
+			| EBackSide | ECanUseSampler | extraFlags 
-		m_components.push_back(
+			| (m_specularReflectance->isConstant() ? 0 : ESpatiallyVarying));
-			EGlossyTransmission | EFrontSide | EBackSide | ECanUseSampler | extraFlags);
+		m_components.push_back(EGlossyTransmission | EFrontSide
+			| EBackSide | ECanUseSampler | extraFlags
+			| (m_specularTransmittance->isConstant() ? 0 : ESpatiallyVarying));
 
 		/* Verify the input parameters and fix them if necessary */
 		m_specularReflectance = ensureEnergyConservation(

src/bsdfs/roughdiffuse.cpp

@@ -107,9 +107,12 @@ public:
 	void configure() {
 		/* Verify the input parameter and fix them if necessary */
 		m_reflectance = ensureEnergyConservation(m_reflectance, "reflectance", 1.0f);
-		
+
 		m_components.clear();
-		m_components.push_back(EGlossyReflection | EFrontSide);
+		m_components.push_back(EGlossyReflection | EFrontSide
+			| ((!m_reflectance->isConstant() || !m_alpha->isConstant())
+			? ESpatiallyVarying : 0));
+
 		m_usesRayDifferentials = m_reflectance->usesRayDifferentials() ||
 			m_alpha->usesRayDifferentials();
 		

src/bsdfs/roughplastic.cpp

@@ -176,8 +176,11 @@ public:
 
 	void configure() {
 		m_components.clear();
-		m_components.push_back(EGlossyReflection | EFrontSide);
+
-		m_components.push_back(EDiffuseReflection | EFrontSide);
+		m_components.push_back(EGlossyReflection | EFrontSide 
+			| (m_specularReflectance->isConstant() ? 0 : ESpatiallyVarying));
+		m_components.push_back(EDiffuseReflection | EFrontSide 
+			| (m_diffuseReflectance->isConstant() ? 0 : ESpatiallyVarying));
 
 		/* Verify the input parameters and fix them if necessary */
 		m_specularReflectance = ensureEnergyConservation(
@@ -357,7 +360,7 @@ public:
 	}
 
 	Spectrum sample(BSDFQueryRecord &bRec, const Point2 &sample) const {
-		Float pdf;
+		Float pdf = 0;
 		Spectrum result = RoughPlastic::sample(bRec, pdf, sample);
 
 		if (result.isZero())

src/bsdfs/ward.cpp

@@ -140,8 +140,11 @@ public:
 			extraFlags |= EAnisotropic;
 
 		m_components.clear();
-		m_components.push_back(EGlossyReflection | EFrontSide | extraFlags);
+		m_components.push_back(EGlossyReflection | EFrontSide | extraFlags
-		m_components.push_back(EDiffuseReflection | EFrontSide | extraFlags);
+			| ((!m_specularReflectance->isConstant() || !m_alphaU->isConstant()
+			  || !m_alphaV->isConstant()) ? ESpatiallyVarying : 0));
+		m_components.push_back(EDiffuseReflection | EFrontSide | extraFlags
+			| (m_diffuseReflectance->isConstant() ? 0 : ESpatiallyVarying));
 
 		/* Verify the input parameters and fix them if necessary */
 		std::pair<Texture *, Texture *> result = ensureEnergyConservation(

src/librender/texture.cpp

@@ -31,7 +31,7 @@ Texture::Texture(Stream *stream, InstanceManager *manager)
 Vector3i Texture::getResolution() const {
 	return Vector3i(0);
 }
-
+	
 Texture::~Texture() {
 }
 

src/textures/bitmap.cpp

@@ -256,6 +256,10 @@ public:
 		return m_maximum;
 	}
 
+	bool isConstant() const {
+		return false;
+	}
+
 	bool usesRayDifferentials() const {
 		return true;
 	}
@@ -353,7 +357,7 @@ public:
 	void unbind() const {
 		m_gpuTexture->unbind();
 	}
-
+	
 	MTS_DECLARE_CLASS()
 private:
 	ref<GPUTexture> m_gpuTexture;

src/textures/checkerboard.cpp

@@ -71,6 +71,10 @@ public:
 		return m_brightColor;
 	}
 
+	bool isConstant() const {
+		return false;
+	}
+
 	std::string toString() const {
 		return "Checkerboard[]";
 	}
@@ -128,7 +132,7 @@ public:
 		program->setParameter(parameterIDs[2], m_uvOffset);
 		program->setParameter(parameterIDs[3], m_uvScale);
 	}
-
+	
 	MTS_DECLARE_CLASS()
 private:
 	Spectrum m_brightColor;

src/textures/gridtexture.cpp

@@ -79,6 +79,10 @@ public:
 	Spectrum getAverage() const {
 		return m_brightColor; // that's not quite right
 	}
+	
+	bool isConstant() const {
+		return false;
+	}
 
 	std::string toString() const {
 		return "GridTexture[]";

src/textures/scale.cpp

@@ -68,6 +68,10 @@ public:
 		return m_nested->getMaximum() * m_scale;
 	}
 
+	bool isConstant() const {
+		return m_nested->isConstant();
+	}
+
 	std::string toString() const {
 		std::ostringstream oss;
 		oss << "ScalingTexture[" << endl

src/textures/vertexcolors.cpp

@@ -54,6 +54,10 @@ public:
 		return Spectrum(1.0f);
 	}
 
+	bool isConstant() const {
+		return false;
+	}
+
 	std::string toString() const {
 		return "VertexColors[]";
 	}