improved reliability of specular perturbations

src/bsdfs/coating.cpp

@@ -225,7 +225,7 @@ public:
 			&& (bRec.component == -1 || bRec.component < (int) m_components.size()-1);
 
 		if (measure == EDiscrete && sampleSpecular &&
-				absDot(reflect(bRec.wi), bRec.wo) > 1-DeltaEpsilon) {
+			    std::abs(dot(reflect(bRec.wi), bRec.wo)-1) < DeltaEpsilon) {
 			return m_specularReflectance->eval(bRec.its) *
 				fresnelDielectricExt(std::abs(Frame::cosTheta(bRec.wi)), m_eta);
 		} else if (sampleNested) {
@@ -274,7 +274,7 @@ public:
 			(1-R12) * (1-m_specularSamplingWeight));
 
 		if (measure == EDiscrete && sampleSpecular &&
-				absDot(reflect(bRec.wi), bRec.wo) > 1-DeltaEpsilon) {
+			    std::abs(dot(reflect(bRec.wi), bRec.wo)-1) < DeltaEpsilon) {
 			return sampleNested ? probSpecular : 1.0f;
 		} else if (sampleNested) {
 			Float R21;

src/bsdfs/conductor.cpp

@@ -229,7 +229,7 @@ public:
 		if (!sampleReflection || measure != EDiscrete ||
 			Frame::cosTheta(bRec.wi) <= 0 ||
 			Frame::cosTheta(bRec.wo) <= 0 ||
-			absDot(reflect(bRec.wi), bRec.wo) < 1-DeltaEpsilon)
+			std::abs(dot(reflect(bRec.wi), bRec.wo)-1) > DeltaEpsilon)
 			return Spectrum(0.0f);
 
 		return m_specularReflectance->eval(bRec.its) *
@@ -245,7 +245,7 @@ public:
 		if (!sampleReflection || measure != EDiscrete ||
 			Frame::cosTheta(bRec.wi) <= 0 ||
 			Frame::cosTheta(bRec.wo) <= 0 ||
-			absDot(reflect(bRec.wi), bRec.wo) < 1-DeltaEpsilon)
+			std::abs(dot(reflect(bRec.wi), bRec.wo)-1) > DeltaEpsilon)
 			return 0.0f;
 
 		return 1.0f;

src/bsdfs/dielectric.cpp

@@ -235,12 +235,12 @@ public:
 		Float F = fresnelDielectricExt(Frame::cosTheta(bRec.wi), cosThetaT, m_eta);
 
 		if (Frame::cosTheta(bRec.wi) * Frame::cosTheta(bRec.wo) >= 0) {
-			if (!sampleReflection || absDot(reflect(bRec.wi), bRec.wo) < 1-DeltaEpsilon)
+			if (!sampleReflection || std::abs(dot(reflect(bRec.wi), bRec.wo)-1) > DeltaEpsilon)
 				return Spectrum(0.0f);
 
 			return m_specularReflectance->eval(bRec.its) * F;
 		} else {
-			if (!sampleTransmission || absDot(refract(bRec.wi, cosThetaT), bRec.wo) < 1-DeltaEpsilon)
+			if (!sampleTransmission || std::abs(dot(refract(bRec.wi, cosThetaT), bRec.wo)-1) > DeltaEpsilon)
 				return Spectrum(0.0f);
 
 			/* Radiance must be scaled to account for the solid angle compression
@@ -262,12 +262,12 @@ public:
 		Float F = fresnelDielectricExt(Frame::cosTheta(bRec.wi), cosThetaT, m_eta);
 
 		if (Frame::cosTheta(bRec.wi) * Frame::cosTheta(bRec.wo) >= 0) {
-			if (!sampleReflection || absDot(reflect(bRec.wi), bRec.wo) < 1-DeltaEpsilon)
+			if (!sampleReflection || std::abs(dot(reflect(bRec.wi), bRec.wo)-1) > DeltaEpsilon)
 				return 0.0f;
 
 			return sampleTransmission ? F : 1.0f;
 		} else {
-			if (!sampleTransmission || absDot(refract(bRec.wi, cosThetaT), bRec.wo) < 1-DeltaEpsilon)
+			if (!sampleTransmission || std::abs(dot(refract(bRec.wi, cosThetaT), bRec.wo)-1) > DeltaEpsilon)
 				return 0.0f;
 
 			return sampleReflection ? 1-F : 1.0f;

src/bsdfs/plastic.cpp

@@ -255,7 +255,7 @@ public:
 		if (hasSpecular) {
 			/* Check if the provided direction pair matches an ideal
 			   specular reflection; tolerate some roundoff errors */
-			if (absDot(reflect(bRec.wi), bRec.wo) > 1-DeltaEpsilon)
+			if (std::abs(dot(reflect(bRec.wi), bRec.wo)-1) < DeltaEpsilon)
 				return m_specularReflectance->eval(bRec.its) * Fi;
 		} else if (hasDiffuse) {
 			Float Fo = fresnelDielectricExt(Frame::cosTheta(bRec.wo), m_eta);
@@ -294,7 +294,7 @@ public:
 		if (hasSpecular && measure == EDiscrete) {
 			/* Check if the provided direction pair matches an ideal
 			   specular reflection; tolerate some roundoff errors */
-			if (absDot(reflect(bRec.wi), bRec.wo) > 1-DeltaEpsilon)
+			if (std::abs(dot(reflect(bRec.wi), bRec.wo)-1) < DeltaEpsilon)
 				return probSpecular;
 		} else if (hasDiffuse && measure == ESolidAngle) {
 			return Warp::squareToCosineHemispherePdf(bRec.wo) * (1-probSpecular);

src/bsdfs/thindielectric.cpp

@@ -163,12 +163,12 @@ public:
 			R += T*T * R / (1-R*R);
 
 		if (Frame::cosTheta(bRec.wi) * Frame::cosTheta(bRec.wo) >= 0) {
-			if (!sampleReflection || absDot(reflect(bRec.wi), bRec.wo) < 1-DeltaEpsilon)
+			if (!sampleReflection || std::abs(dot(reflect(bRec.wi), bRec.wo)-1) > DeltaEpsilon)
 				return Spectrum(0.0f);
 
 			return m_specularReflectance->eval(bRec.its) * R;
 		} else {
-			if (!sampleTransmission || absDot(transmit(bRec.wi), bRec.wo) < 1-DeltaEpsilon)
+			if (!sampleTransmission || std::abs(dot(transmit(bRec.wi), bRec.wo)-1) > DeltaEpsilon)
 				return Spectrum(0.0f);
 
 			return m_specularTransmittance->eval(bRec.its) * (1 - R);
@@ -188,12 +188,12 @@ public:
 			R += T*T * R / (1-R*R);
 
 		if (Frame::cosTheta(bRec.wi) * Frame::cosTheta(bRec.wo) >= 0) {
-			if (!sampleReflection || absDot(reflect(bRec.wi), bRec.wo) < 1-DeltaEpsilon)
+			if (!sampleReflection || std::abs(dot(reflect(bRec.wi), bRec.wo)-1) > DeltaEpsilon)
 				return 0.0f;
 
 			return sampleTransmission ? R : 1.0f;
 		} else {
-			if (!sampleTransmission || absDot(transmit(bRec.wi), bRec.wo) < 1-DeltaEpsilon)
+			if (!sampleTransmission || std::abs(dot(transmit(bRec.wi), bRec.wo)-1) > DeltaEpsilon)
 				return 0.0f;
 
 			return sampleReflection ? 1-R : 1.0f;

src/libbidir/vertex.cpp

@@ -710,7 +710,13 @@ bool PathVertex::propagatePerturbation(const Scene *scene, const PathVertex *pre
 
 	bRec.typeMask = BSDF::EAll;
 	Float prob = bsdf->pdf(bRec, EDiscrete);
-	weight[mode] = bsdf->eval(bRec, EDiscrete)/prob;
+	if (prob == 0) {
+		SLog(EWarn, "Unable to recreate specular vertex in perturbation (bsdf=%s)",
+			bsdf->toString().c_str());
+		return false;
+	}
+
+	weight[mode] = bsdf->eval(bRec, EDiscrete) / prob;
 	pdf[mode] = prob;
 	measure = EDiscrete;
 	componentType = componentType_;