Propose a solution about fixing connection of delta emitters to senso…

src/integrators/ptracer.cpp

@@ -110,7 +110,9 @@ class ParticleTracerIntegrator final : public AdjointIntegrator<Float, Spectrum>
             dr::gather<EmitterPtr>(scene->emitters_dr(), emitter_idx);
 
         // Don't connect delta emitters with sensor (both position and direction)
-        Mask active = !has_flag(emitter->flags(), EmitterFlags::Delta);
+        // Unless the sensor has spatial extent (e.g. irradiancemeter)
+        Mask active = !has_flag(emitter->flags(), EmitterFlags::Delta) ||
+                      sensor->needs_aperture_sample();
 
         // 3. Emitter position sampling
         Spectrum emitter_weight = dr::zeros<Spectrum>();
@@ -347,7 +349,9 @@ class ParticleTracerIntegrator final : public AdjointIntegrator<Float, Spectrum>
         // Foreshortening term and BSDF value for that direction (for surface interactions).
         Spectrum result = 0.f;
         Spectrum surface_weight = 1.f;
-        Vector3f local_d        = si.to_local(sensor_ray.d);
+        Mask has_frame          = dr::norm(si.n) > 0.f;
+        Vector3f local_d        = dr::zeros<Vector3f>();
+        local_d[has_frame]      = si.to_local(sensor_ray.d);
         Mask on_surface         = active && (si.shape != nullptr);
         if (dr::any_or<true>(on_surface)) {
             /* Note that foreshortening is only missing for directly visible
@@ -382,7 +386,7 @@ class ParticleTracerIntegrator final : public AdjointIntegrator<Float, Spectrum>
            we still don't want light coming from behind the emitter. */
         Mask not_on_surface = active && (si.shape == nullptr) && (bsdf == nullptr);
         if (dr::any_or<true>(not_on_surface)) {
-            Mask invalid_side = Frame3f::cos_theta(local_d) <= 0.f;
+            Mask invalid_side = has_frame && (Frame3f::cos_theta(local_d) <= 0.f);
             surface_weight[not_on_surface && invalid_side] = 0.f;
         }
 

src/integrators/tests/test_ptracer.py

@@ -234,3 +234,37 @@ def __init__(self, props):
     mi.load_dict({
         'type': 'myptracer'
     })
+
+
+def test08_delta_light_irradiancemeter(variants_all_ad_rgb):
+    scene_dict = {
+        'type': 'scene',
+        'integrator': {
+            'type': 'ptracer',
+            'max_depth': 2,
+        },
+        'sensor': {
+            'type': 'sphere',
+            'center': [0, 0, 0],
+            'radius': 1.0,
+            'sensor': {
+                'type': 'irradiancemeter',
+                'film': {
+                    'type': 'hdrfilm',
+                    'width': 1,
+                    'height': 1,
+                    'rfilter': {'type': 'box'},
+                }
+            }
+        },
+        'emitter': {
+            'type': 'point',
+            'position': [2, 0, 0]
+        }
+    }
+
+    scene = mi.load_dict(scene_dict)
+    sensor = scene.sensors()[0]
+    image = mi.render(scene, seed=0, sensor=sensor)
+
+    assert image[0][0][0].numpy() > 0.1

src/sensors/irradiancemeter.cpp

@@ -101,7 +101,9 @@ MI_VARIANT class IrradianceMeter final : public Sensor<Float, Spectrum> {
 
     std::pair<DirectionSample3f, Spectrum>
     sample_direction(const Interaction3f &it, const Point2f &sample, Mask active) const override {
-        return { m_shape->sample_direction(it, sample, active), dr::Pi<ScalarFloat> };
+        DirectionSample3f ds = m_shape->sample_direction(it, sample, active);
+        return { ds, dr::select(ds.pdf > 0.f,
+                                dr::rcp(ds.pdf) / m_shape->surface_area(), 0.f) };
     }
 
     Float pdf_direction(const Interaction3f &it, const DirectionSample3f &ds,

src/sensors/tests/test_irradiancemeter.py

@@ -114,7 +114,8 @@ def test_incoming_flux(variant_scalar_rgb, radiance, np_rng):
 
 
 @pytest.mark.parametrize("radiance", [2.04, 1.0, 0.0])
-def test_incoming_flux_integrator(variant_scalar_rgb, radiance):
+@pytest.mark.parametrize("integrator_type", ["path", "ptracer"])
+def test_incoming_flux_integrator(variant_scalar_rgb, radiance, integrator_type):
     """
     We test the recorded power density of the irradiance meter, by creating a simple scene:
     The irradiance meter is attached to a sphere with unit radius at the coordinate origin
@@ -129,17 +130,21 @@ def test_incoming_flux_integrator(variant_scalar_rgb, radiance):
         'type': 'scene',
         'sensor': sensor_shape_dict(1, mi.ScalarVector3f(0, 0, 0)),
         'emitter': constant_emitter_dict(radiance),
-        'integrator': {'type': 'path'}
+        'integrator': {'type': integrator_type},
+        'sampler': {
+            'type': 'independent',
+            'sample_count': 4000  
+        }
     }
 
     scene = mi.load_dict(scene_dict)
-    scene.integrator().render(scene, seed=0)
+    scene.integrator().render(scene, seed=0, spp=10000)
     film = scene.sensors()[0].film()
 
     img = film.bitmap(raw=True).convert(mi.Bitmap.PixelFormat.Y,
                                         mi.Struct.Type.Float32, srgb_gamma=False)
 
-    assert dr.allclose(mi.TensorXf(img), (radiance * dr.pi))
+    assert dr.allclose(mi.TensorXf(img), (radiance * dr.pi), rtol=0.2)
 
 
 def test_shape_accessors(variants_vec_rgb):