But even though we had a competent rendering engine from PGR4, we couldn't have used it for Blur. This was because it was single-threaded renderer which was written for 360, porting it to PS3 would have been very difficult, and anyway it was pretty much at its limits with eight cars and no other dynamic objects on track.
This wouldn't be good enough for Blur, so we took everything we learned from the PGR engine and also our experience on The Club and started from scratch on a new rendering engine which would take full advantage of the 360 and PS3s multi-core architecture.
This new engine, which we've dubbed "Horizon", is what we're using on Blur. So, whereas on PGR4 we would generally spend 15+ms rendering on one CPU, with Horizon we now spend more like 5-8ms doing rendering across all cores/SPUs simultaneously, and we're rendering a lot more stuff than we ever did in PGR.