Add two sided area lights

nori/include/nori/arealight.h

@@ -114,7 +114,7 @@ public:
     float phi = M_PI * area * m_radiance.maxCoeff();
     BoundingBox3f bbox = triangle->getBoundingBox(0);
     Vector3f n = triangle->getNormal();
-    return EmitterBounds(bbox, n, phi, 1, 0);
+    return EmitterBounds(bbox, n, phi, 1, 0, true);
   }
 
   virtual bool isAreaLight() const override { return true; }

nori/include/nori/emitter.h

@@ -39,11 +39,11 @@ struct EmitterBounds {
 
   EmitterBounds()
       : bounds(BoundingBox3f(Point3f::Zero())), w(Vector3f::Zero()), phi(0),
-        cosTheta_o(1), cosTheta_e(0){};
+        cosTheta_o(1), cosTheta_e(0), twoSided(false) {};
   EmitterBounds(const BoundingBox3f &bounds, const Vector3f &w, float phi,
-                float cosTheta_o, float cosTheta_e)
+                float cosTheta_o, float cosTheta_e, bool twoSided)
       : bounds(bounds), w(w), phi(phi), cosTheta_o(cosTheta_o),
-        cosTheta_e(cosTheta_e){};
+        cosTheta_e(cosTheta_e), twoSided(twoSided){};
 
   Point3f centroid() const { return bounds.getCenter(); }
 
@@ -66,6 +66,9 @@ struct EmitterBounds {
 
     Vector3f wi = (p - bound_center).normalized();
     float cos_theta = wi.dot(w);
+    if (twoSided) {
+      cos_theta = abs(cos_theta);
+    }
     float sin_theta = sqrt(1.f - cos_theta * cos_theta);
 
     // this is a valid formulation for cos(max(a - b, 0)) for a, b in [0, pi]
@@ -126,7 +129,7 @@ struct EmitterBounds {
                        "cosTheta_o=%f,\n"
                        "two_sided=%d ]",
                        bounds.toString(), w.toString(), phi, cosTheta_o,
-                       cosTheta_e, two_sided);
+                       cosTheta_e, twoSided);
   }
 
   BoundingBox3f bounds;
@@ -136,7 +139,7 @@ struct EmitterBounds {
   float phi = 0; // total power of the light
   float cosTheta_o, cosTheta_e;
   // nori does not handle two sided light sources at the moment
-  bool two_sided = false;
+  bool twoSided = false;
 
   static EmitterBounds merge(const EmitterBounds &a, const EmitterBounds &b) {
     if (a.phi == 0) {
@@ -154,7 +157,7 @@ struct EmitterBounds {
     ext_bounds.expandBy(b.bounds);
 
     return EmitterBounds(ext_bounds, cone.w, a.phi + b.phi, cos_theta_o,
-                         cos_theta_e);
+                         cos_theta_e, a.twoSided | b.twoSided);
   }
 };
 

nori/src/envmap.cpp

@@ -198,7 +198,7 @@ public:
     const float phi =
         (M_PI * m_radius * m_radius * colorLookup(Point2f(.5f, .5f)))
             .maxCoeff();
-    return EmitterBounds(sphere_bounds, Vector3f::UnitZ(), phi, -1, 0);
+    return EmitterBounds(sphere_bounds, Vector3f::UnitZ(), phi, -1, 0, false);
   }
 
   virtual Color3f samplePhoton(Ray3f &ray, const Point2f &sample1,

nori/src/path_mis.cpp

@@ -34,11 +34,13 @@ public:
       if (!scene->rayIntersect(ray, its)) {
         break;
       }
-      ctx = LightSamplingContext(its.p, its.shFrame.n);
 
       if (its.mesh != nullptr && its.mesh->isEmitter()) {
         lRec = EmitterQueryRecord(ray.o, its.p, its.shFrame.n);
+        ctx = LightSamplingContext(its.p, its.shFrame.n);
 
+        // the light pdf is the product of the emitter pdf and the pmf of
+        // sampling that light
         mat_light_pdf = its.mesh->getEmitter()->pdf(lRec) *
                         m_light_sampler->pmf(ctx, its.mesh->getEmitter());
         w_mat = bRec.measure != EMeasure::ESolidAngle
@@ -71,15 +73,14 @@ public:
       // do {
       //   light = m_light_sampler->sample(ctx, sampler->next1D());
       // } while (light == nullptr);
-
-      Emitter* light = m_light_sampler->sample(ctx, sampler->next1D());
-      if (!light) break;
+      ctx = LightSamplingContext(its.p, its.shFrame.n);
+      Emitter *light = m_light_sampler->sample(ctx, sampler->next1D());
+      if (!light)
+        break;
 
       lRec_light.ref = its.p;
-      // light power needs to be scaled by the inverse pdf of choosing that
-      // light
-      Color3f Le_2 = light->sample(lRec_light, sampler->next2D());
-      em_light_pdf = light->pdf(lRec_light) * ctx.pdf;
+      Color3f Le_2 = light->sample(lRec_light, sampler->next2D()) / ctx.pdf;
+      em_light_pdf = ctx.pdf * light->pdf(lRec_light);
 
       if (!scene->rayIntersect(lRec_light.shadowRay, its_nee) ||
           its_nee.mesh->isEnvironmentLight()) {
@@ -94,8 +95,8 @@ public:
         w_em = isnan(w_em) ? 0.f : w_em;
 
         float cos_theta = std::max(0.f, Frame::cosTheta(bRec_light.wo));
-        Li +=
-            w_em * t * cos_theta * its.mesh->getBSDF()->eval(bRec_light) * Le_2;
+        Color3f f_a = its.mesh->getBSDF()->eval(bRec_light);
+        Li += w_em * t * cos_theta * f_a * Le_2;
       }
 
       t *= f;

nori/src/pointlight.cpp

@@ -35,7 +35,7 @@ public:
 
   virtual EmitterBounds bounds() const override {
     BoundingBox3f bbox{};
-    return EmitterBounds(bbox, Vector3f::UnitZ(), m_power.maxCoeff(), -1, 0);
+    return EmitterBounds(bbox, Vector3f::UnitZ(), m_power.maxCoeff(), -1, 0, false);
   }
 
   std::string toString() const {

scenes/nori/cbox/cbox_many_mls.xml

@@ -3,7 +3,6 @@
 <scene>
 	<integrator type="path_mis">
 		<lightsampler type="mls" />
-		<!-- <lightsampler type="uniform_light" /> -->
 	</integrator>
 
 	<camera type="perspective">
@@ -18,7 +17,7 @@
 	</camera>
 
 	<sampler type="independent">
-		<integer name="sampleCount" value="16" />
+		<integer name="sampleCount" value="32" />
 	</sampler>
 
 	<mesh type="obj">
@@ -60,10 +59,10 @@
 	</mesh>
 
 	<mesh type="obj">
-		<string name="filename" value="meshes/100_lights.obj" />
+		<string name="filename" value="meshes/1000_lights.obj" />
 
 		<emitter type="area">
-			<color name="radiance" value="1 1 1" />
+			<color name="radiance" value="15 15 15" />
 		</emitter>
 	</mesh>
 </scene>
\ No newline at end of file

scenes/nori/cbox/cbox_many_uniform_light.xml

@@ -17,7 +17,7 @@
 	</camera>
 
 	<sampler type="independent">
-		<integer name="sampleCount" value="16" />
+		<integer name="sampleCount" value="32" />
 	</sampler>
 
 	<mesh type="obj">
@@ -59,10 +59,10 @@
 	</mesh>
 
 	<mesh type="obj">
-		<string name="filename" value="meshes/100_lights.obj" />
+		<string name="filename" value="meshes/1000_lights.obj" />
 
 		<emitter type="area">
-			<color name="radiance" value="1 1 1" />
+			<color name="radiance" value="15 15 15" />
 		</emitter>
 	</mesh>
 </scene>
\ No newline at end of file