[BUG] Phong Normalized does not set pdf + possibly wrong brdf value
In the phong.cu, in function "sample_and_eval", the varying parameter "pdf" is not set, leading to potential in the MIS computation.
Also, I think the BRDF value is wrongly computed in this same function. The process is as follows: 1 - choose if sampling the diffuse or specular part. 2 - if sampling the diffuse part: sample cos weighted hemisphere and brdf = diffuse_color. 3 - if sampling the diffuse part: sample phong lobe and brdf = specular_color * phong_blahblah.
While I agree on the fact that we must "randomly" choose between sampling using cos or the phong lobe, I disagree that the BRDF should be only a restriction and not the full phong brdf (diffuse_color + specular_color).
Or if it should, then the function "brdf_eval" must also use the same principle, whereas it currently evaluate the full phong BRDF without choose between diffuse or specular.