Watching the original Toy Story, I found myself wondering why Pixar doesn't release older versions of their rendering software for use in video games. I was hoping it was a technical issue, rather than an intellectual property one, since clearly Pixar's rendering is only a fraction of their unstoppable creative genius.
Thankfully, it appears my hunch was right, and it seems that the Pixar RenderMan software is fundamentally not designed for real-time rendering, a necessity for video gaming systems.
This reminds me of one of the basic-truths of real-time: that you'll always give something up. Any real-time system is living under constraints, and as it turns out, the RenderMan shader language simply doesn't play by those rules. Luckily for us, it doesn't need to be real-time to generate stunning animated films.