SurfaceInteraction is not valid for any ray

[Hochheilige]

Hello, I'm trying to implement custom Integrator in Mitsuba and it looks like this right now:

class RHSIntegrator(ADIntegrator):
    def __init__(self, model, props=mi.Properties()):
        super().__init__(props)
        self.model = model

    @dr.syntax
    def sample(self,
               mode: dr.ADMode,
               scene: mi.Scene,
               sampler: mi.Sampler,
               ray: mi.Ray3f,
               depth: mi.UInt32,
               δL,
               δaovs,
               state_in,
               active):
        w, h = list(scene.sensors()[0].film().size())
        L = mi.Spectrum(0)

        ray = mi.Ray3f(dr.detach(ray))
        si = scene.ray_intersect(
            ray, ray_flags=mi.RayFlags.All, coherent=(depth == 0)
        )

        # update si and bsdf with the first non-specular ones
        si, β, _ = first_non_specular_or_null_si(scene, si, sampler)
        L = render_rhs(scene, self.model, si, sampler)

        torch.cuda.empty_cache()
        return β * L, si.is_valid(), []
       
rhs_integrator = RHSIntegrator(field)
rhs_image = mi.render(scene, spp=4, integrator=rhs_integrator)

and if I test si.is_valid after scene._ray_intersect than I see False for all si I have. Why it can happen? My scene is just basic cornell box and it renders okay without custom integrator

[njroussel]

I see that you closed this, did you figure it out?

[Hochheilige]

Yeah I thought that my problem was related to SurfaceInteraction, but actually no. And my integrator didn't render anything because I returned 3 variables not 4 as needed