PT Slow Render Times

Started by WAS, September 22, 2021, 12:23:14 PM

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Hate to bring this up again, but I think it deserves more discussion and hopefully we can fix it.

I am starting to think slow PT times are exclusively at the fault of the dynamic micropolygon adaption. For example, I am doing a scene that I watched fully render out to the floor plane at 9PM last night over just a short hour. The rest of the time it's been rendering the TG primitve plane. I think these surfaces are too complex for the PT and should be approximated much more for render times. Especially if they're simple in geometry (a plane with no displacement).

This render has spent 12 hours just doing a reflective plane, but everything else that is chromed out rendered in an hour as imported geometry last night.

I hate to be that guy again, but this is pretty ridiculous and speaks volumes to TGs effectiveness in modern rendering. Something has to be done.


Additionally, I had to planes as a portal, but TG couldn't do glass transparency with haze, so I had to make two circle planes in Blender. Even those render 100x faster then the TG planes with same textures applied. Glass and PF lum. One of the planes is even subdivided up to over 500mb for TG force displacement, and still had no issues compared to TG plane.


PS; this isn't a slowdown of buckets, all the buckets are going at 81-100% CPU utilization.


It could be the volumetric/media that is slowing down reflections, really clean volumetric media can be pretty time consuming. Still, this is pretty slow, maybe there's some excessive sampling somewhere that is not exposed anywhere and just fails to be efficient in this special case.

A honest question - did you consider other 3d apps for this kind of setups? I sometimes see scenes that would be much less a headache to produce in other 3ds apps. TG has some really cumbersome or extremely limited workflows for scene assembly/management, objects, scattering, manipulation, materials, animation etc. I wouldn't even think about using TG for most stuff, I personally think it's best suited for landscapes/nature, atmosphere and planets, and it can already be pretty cumbersome to work with in these cases. Not to sound like a smart*** but I think a different app would really be a better tool in this case.

Still, it's good someone checks the depths of PT in TG, it can be probably improved to be more efficient in other scenarios than what people typically do in TG.


I'd think the same thing with volume if it wasn't for the same chrome / steel materials and roughness used (besides crystals which is a mix of image and the PF used elsewhere) for everything in the scene. The top portion all the way almost up to the floor plane rendered in about an hour last night. Now at 12 hours, still waiting on that plane to finish.

And yeah, ofc I do. I actually have the same scene in works in Blender, but I am most familiar with Terragen these days, as I come from C4D, which I had one disc and have obviously lost when we lost our storage unit. I had held out hope. So all I have for DCC is Terragen, Blender, Photoshop CS5 (or 2020-2021 if I use a buddies PC I have had for a while). I am actually just now really starting to learn to Blender because of the need for certain objects I needed within Terragen, and found my way playing with displacements and noises and really love how quick it is to create pretty convincing rock shapes.

I have this suspicion that TG objects get heavily subdivided in instances where they may not need to be, which strains the PT samplers trying to calculate face bounce. Or maybe it's a combination of issues, like dynamically calculating subdivision then immediately calculating bounce at that pixel in just a way that is slow for the CPU or something.

In general, though, we don't have GPU support in Terragen. While I do think Blenders cycles CPU is a bit faster then Terragen, I am mainly using the GPU version on my RX 580 4GB and it's pretty fast for base 128 samples (haven't had a 1080p cycles GPU render exceed 5 minutes!).


Here is the scene so far in Blender GPU Cycles. Little over a minute to render without volumes added yet (I don't know how :-X :-[ )

PBR textures sure look a lot better in Blender. Not sure why, I followed our usual procedure for PBR in TG. Need to crank up the lights but gotta figure out what I did wrong in TG.

Luminosity lighting is a lot nicer to. Can't wait for that to be better in TG. Especially without needing a dupe obj for emission strength.while retaining colour.


PT render time is one of my major 'concerns' of TG. It is beautiful, but indeed, the displaced/reflected/transparent micropoly parts take up the most time. Like in my glacier scene; the glacier doesn't really benefit from PT much (people and veggies do), but does take most of the time.
So that would be my top priority; try to sample differently, approximate more, or add a GPU renderer. But if that were easy, Matt would probably have done so already :P
I am really a TG addict, using it every day, so....


Quote from: Dune on September 23, 2021, 02:34:06 AMMatt would probably have done so already :P
I am really a TG addict, using it every day, so....
Very true, and I am the same. While I am liking blender a bit, I still like Terragen more, and even today working on my projected opened Terragen a few times to doodle out some ideas.

One thing i have to mention, TGs PT renders are a lot less noisy then Blender. Blender uses 128 samples. I don't know what that translates to in TG, but it's very noisy, but with the denoiser active it can look decent, but it ruins soft stuff. So I am now using the render layers and the intel AI denoiser shader, which gives a lot better results. But again, it's denoising, where TG is brute forcing PT to look beautiful on it's own with minimal noise and rogue pixelation (sparkles of light far from source). So I think while TG's PT is way slow in some aspects, it's quality is far better "out of the box" without needing denoising. But that also may be why renders are taking so long.

Attached my cycles 1080p scene where I'm at currently. Struggling with volume. I can't get any details to show with my noise texture, but it helps the lighting a lot even if solid. Still 7m vs 16hr is pretty dramatic... (i have yet to finish my one TG PT, it's been paused since earlier).

Also ran the 4k textures for those crystals through gigapixel at 16k now, soooo much nicer looking.


So little update: Blenders path tracer may do surfaces quicker than TG, but when it comes to Subsurface Scattering, and Volumetrics, Blender is leagues behind imo. It's so slow it's not even funny. Also their optimization of renders is garbage imo. Also some stuff makes no sense. Like I changed default 128 samples to 1024, takes 7 minutes, change it to 4096, and it took almost 9 minutes, so hey, why not 8196? No. Woke up and it hadn't even finsihed the first buckets assigned. What a crazy jump in times. And from what I see what it was working on was just as noisy as 4096 samples.