fxguide’s Mike Seymor has a fantastic article online about the complexity of scene renderers. Not only does he get into the mathematics behind physical lighting effects like global illumination, sub-surface scattering, BRDF’s, and more, he goes in depth with several of the biggest packages out today to see where they excel.
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.
