FXGuide has a fantastic writeup on “The Art of Rendering” that covers various optimization techniques to speed up high-quality renders into multiple passes, and then breaks it all down into various studio approaches and individual software programs.
Renderers are easy to write in the abstract, as perhaps a university project, but to work in production environments is extremely difficult. Arnold, by Solid Angle, is some 200,000 lines of highly optimized C++ code, and it is considered a very direct implementation without a lot of hacks or tricks. Production requirements in terms of rendertime and scene complexity are staggering. And the problem is not just contained to final render time, as Arnold founder Marcos Fajardo pointed out at Siggraph 2010 – final render CPU time might cost $0.10 per hour, but artist time is closer to $40 an hour, so interactivity is also vital.
They have a great catalog of app results as well including Houdini, Modo, Renderman, Vray, and several others.
