The Bathroom is a typical interior scene with a mix of textured glossy and diffuse materials that is easy to render for a unidirectional path tracer due to large light sources: the windows are modeled as diffuse area emitters. The bump-mapped surfaces are a challenge for local-frame-based guiding methods, such as the GMMs by Vorba et al. [2014] and are handled more gracefully by world-frame-based techniques such as PPG [Müller et al. 2017] and our NPG. In this scene, radiance-based guiding performs worse than unidirectional path tracing due to a rough dielectric glass panel directly in front of the light sources. Product-based techniques, like our NPG-Product, are able to take such BSDF properties into account and are able to significantly improve upon the performance of unidirectional path tracing at equal sample counts. 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.

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