Computing Gauss-Legendre quadrature points and weights

[PolyRocketMatt]

In constructing our BRDF plugin for Mitsuba 3, we are required to use a quadrature. Since Mitsuba provides methods to compute both gauss-legendre and gauss-lobatto points and weights in include/mitsuba/core/quad.h, this seems like the go-to method. We therefor include this file:

#include <mitsuba/core/quad.h>

The gauss-legendre/lobatto methods return a tuple representing the points and weights. It requires a dynamic type to store these in. Therefore, we constructed a type alias FloatStorage which is defined in a similar way as in inlude/mistuba/core/distr_2d.h as follows:

using FloatStorage = DynamicBuffer<Float>;

Next, in the relevant method, we compute the quadrature points and weights:

Float compute_quadrature() {
    ...
    std::pair<FloatStorage, FloatStorage> quad_result = quad::gauss_legendre<FloatStorage>(24);
    ...
}

This properly compiles. However, the problem arises whenever we try to evaluate our BRDF (which calls the compute_quadrature() function). When running from python, we receive the following error:

Critical failure in Dr.Jit AD backend: referenced an unknown variable a1065961051!
Aborted

This is all the information we were able to retrieve. Thanks in advance.

[njroussel]

Hi @PolyRocketMatt

A lot of stuff could be wrong here, I'm going to need a need bit more information. How are you using the points and weights? Could you provide me with a minimal reproducer, just a dummy BSDF that recreates the error is fine?