Quote - I had a rust shader in the Chevy but Tom said it was not good enough because it was too uniformly distributed. Rust needs to be controlled where it shows, otherwise it looks fake. So a generic shader driven by a control map would work, but you have to make a unique control map for each vehicle.

I kind of thought that would be the case... otherwise I guess you'd need to be able to tell a shader to treat different parts differently based on some sort of "physical" rules... rust, I guess, apart from around random chip spots on the main body (caused by small stones etc. being thrown up from the road) usually forms around lower, more exposed edges on a vehicle, facing the road surface... there's some sort of dynamics in there somewhere, probably...??? Maybe just orientation awareness, on a par with, for example, the Snow Machine script though?

Overall, it's maybe not disimilar to the issues around generating a full body's worth of convincing, procedural human skin I guess?