The Bookshelf scene is very difficult to render with unidirectional path tracing due to complex glossy interreflections and light sources encased by glass. Radiance-based path guiding is highly effective at rendering this scene, with the GMMs by Vorba et al.  performing the best among all approaches. Primary-sample-space path-sampling techniques offer little to no benefit over unidirectional path tracing with our NPS slightly outperforming PSSPS [Guo et al. 2018] with an equal number of samples.