The article <a href="https://fabiensanglard.net/postcard_pathtracer/" author="Fabien Sanglard">Deciphering The Postcard Sized Raytracer</a> is a wonderfully presented breakdown of how the <i>path</i> tracer found on a postcard does its magic. It's not super-fast (it takes 3 minutes to produce a much rougher version on the author's machine). He includes his final <a href="https://fabiensanglard.net/postcard_pathtracer/formatted_full.html">cleaned-up source code</a>. <img src="{att_link}rendered_pixar.png" href="{att_link}rendered_pixar.png" align="none" scale="50%"> It comes from the same person who made the business card ray-tracer discussed in the article <a href="https://fabiensanglard.net/rayTracing_back_of_business_card/" author="Fabien Sanglard">Decyphering The Business Card Raytracer</a>.