> what's the importance of improving existing ray tracers In the offline space (film, visualization), cost. Movies get cheaper to make. In the realtime space

> what's the importance of improving existing ray tracers In the offline space (film, visualization), cost. Movies get cheaper to make. In the realtime space (games), lots of visually important effects are difficult to do with rasterization, leading to complicated/large/expensive-to-maintain rendering solutions. With a physically based path tracer, a lot of these effects come out of the box. Path tracing has traditionally been too expensive to do in realtime, however, and has been 'just around the corner' for the past 20 years. If I'm not mistaken, recent advances in image de-noising, which seems to be the crux of the new NVIDIA technology, have made real time path-tracing on the GPU much more practical. > Is writing one a particularly challenging thing to do? Depends how deep you dive. You can write a basic tracer to render a sphere and fit it on a business card -- this is a typical assignment in introductory graphics courses. Rendering complicated materials is a never ending rat hole of complexity, lots of rendering research looks effectively like material's science, these days.