Added filter size check

Author: leroyvn

src/sensors/radiancemeter.cpp

@@ -77,6 +77,11 @@ MTS_VARIANT class RadianceMeter final : public Sensor<Float, Spectrum> {
 
         if (m_film->size() != ScalarPoint2i(1, 1))
             Throw("This sensor only supports films of size 1x1 Pixels!");
+
+        if (m_film->reconstruction_filter()->radius() >
+            0.5f + math::RayEpsilon<Float>)
+            Log(Warn, "This sensor should be used with a reconstruction filter "
+                      "with a radius of 0.5 or lower (e.g. default box)");
     }
 
     std::pair<Ray3f, Spectrum> sample_ray(Float time, Float wavelength_sample,
@@ -119,7 +124,7 @@ MTS_VARIANT class RadianceMeter final : public Sensor<Float, Spectrum> {
         ray.o      = trafo.transform_affine(Point3f{ 0.f, 0.f, 0.f });
         ray.d      = trafo.transform_affine(Vector3f{ 0.f, 0.f, 1.f });
 
-        // 3. Set differentials; since the film size is always 1x1, we don't 
+        // 3. Set differentials; since the film size is always 1x1, we don't
         //    have differentials
         ray.has_differentials = false;