The 2nd Compute Terrain is probably unnecessary in this case, yes. Although there is one Power Fractal between it and the first Compute Terrain that is providing displacement, it is plugged in to the Color input of a Surface Layer so I don't think it's actually causing displacement that would need the re-compute of terrain for proper population placement.
When I first looked at this scene I wasn't quite sure where the render time was coming from. The atmosphere is up at 32 samples which, when using Raytraced Atmosphere and an AA of 6, is really unnecessary, so that should be down more around say 12. But the cloud samples were fine, albeit with no acceleration cache, but as a 2D layer with minimal samples it really shouldn't matter. And indeed that was the case, when I started a (much lower resolution) test render, the sky rendered quickly. I expected the water to be the next slowest thing, but in fact it took ages just to render the terrain, 28 minutes and the scene had only rendered 38% on my overclocked i7 quad at 4.6Ghz. So I knew something odd was going on...
With the terrain taking so long, I started digging around in the surfacing nodes and found tons of nesting and very complex surfaces. The surfacing work in the scene is nice, but this is still probably overly complex. The real culprit though?
Reflective shader with raytraced reflections in one of the Fake Stones layers! Once I simply disabled the raytraced reflections, the entire scene at the same resolution and detail as before took only 13 minutes to render *completely*. That's less than 1/4 of the render time (projected) as before, and that's just from disabling one unnecessary setting.
Beyond that you could probably simplify the surfacing quite a bit, and there are other reflective layers too that are of questionable necessity, but none I saw with
raytraced reflections enabled, which will really kill your render time, especially for complex displaced surfaces. It's also not going to contribute noticeably to a scene like this so it's really just wasted time.
In addition to that, I think detail 0.9 is probably overkill. I've tweaked that and a few other settings and attached a modified TGD. This should render a *lot* faster and give you a near identical result. It took only 10 minutes on my machine, compared to 13 minutes for the scene just without raytraced reflections, and a projected 1hr+ in the original config. If you find you still want more detail, up the main detail back to 0.9, but I really think 0.75 should do. I've actually increased the AA to give you better smoothing on your complex plants since you'll be saving a lot of render time in other areas, and I also upped raytracing quality so your water reflections look better, and still a ton of render time is saved due to not raytracing reflections on those stones. I predict this will render in about 10 hours at full resolution.
As I said you could probably save even more render time if you simplified the surface mapping a bit, for example consider removing all the reflective shaders entirely, I'm really dubious whether they actually add anything visibly to the scene.
- Oshyan
