work-around for slow PT reflection calculation

Started by Dune, March 23, 2021, 12:41:48 PM

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WAS

Definitely gets slower once you start approaching the detail of the original terrain. I'd say this is a little over half quality of the original terrain, and render time shows it.

With objects, there is no adaptive terrain, and other stuff effecting things, so I can see why they are even faster than a heightmap.

This is now a 8196x8196 at 1000m instead of 10000m. Shaders are culled to displacement so you can see where they end now, but in full scene that area could be easily hidden. It offers some render performance gain at the clear cost of quality. So a obj may be better unless further away from the focal.

Kadri

Quote from: WAS on March 24, 2021, 03:49:14 PMIt's faster because of the detail of the mesh of the planet at the heightfield area.

As I've stated several times, you could have hundreds of shaders slowing TG down, or just a few, but as soon as it's a heightmap and simplified, it's far faster. At the cost of geomerty detail. Hence adding displacement, or lateral dispalcement, etc, is just a mess of folds and tears. ...
Eee...i said the same. I tried at least... "using less detail" should have been "from having less detail" in my post...
I should sleep. See you later.

WAS

Quote from: Kadri on March 24, 2021, 04:18:41 PM
Quote from: WAS on March 24, 2021, 03:49:14 PMIt's faster because of the detail of the mesh of the planet at the heightfield area.

As I've stated several times, you could have hundreds of shaders slowing TG down, or just a few, but as soon as it's a heightmap and simplified, it's far faster. At the cost of geomerty detail. Hence adding displacement, or lateral dispalcement, etc, is just a mess of folds and tears. ...
Eee...i said the same. I tried at least... "using less detail" should have been "from having less detail" in my post...
I should sleep. See you later.
Well Ive said that since the get go, so I am not sure what you meant beyond what Ive already said here and in other topics.

Kadri

The main thing was that Terragen renders micropolygons and objects different in my post.

Anyway...

Using objects looks better then.

WAS

Yeah I mentioned it's probably best. 

If you subdivide enough too you could probably also use force displacement to doctor it

Dune

Thanks for diving into this. It doesn't seem that straightforward. I found that rendering in PT of the same textures on a flat imported extremely low-poly object takes about just as long, even if the displacements are then only bump. TG still needs to calculate the light and bounces, I guess.
For my scene only the first 5m or so are very slow, so I should make that area into a very finely displaced mesh. Or sculpt something like it in ZB. But actually, that workaround might take more active time than just have it render.
Or maybe rotate the camera 180ยบ or do it in crops.
Or just work in SR. It needs to be a series of low paid 6000x4000 renders, so I'm not looking forward to a week of rendering.
Or perhaps make the ground drier.

Kadri

Still curious if an exported object would be faster or not. Your test does have displacement made with Terragen going on.
Not saying that it would be faster but your test is a little different.

Dune

The foreground is just tiny displacements, like soil, so a sculpted plane in hires might be just as easy to import. Rather than having to export an obj. Dip the planet ground a bit and have the object fit into that place, add just textures... render. I might give it a try. But actually, I can't imagine it would be much faster, as the reflections on that sculpted obj still need computing across the slopes and angles... So why your test gives such a difference in rendertime eludes me.

Matt

#38
Quote from: Dune on March 24, 2021, 05:26:59 AMI have probably answered my own question. If you use the default shader and no fresnel reflectivity, but just metallic and some bluish color (or maybe a color map), rough ground PT renders very much faster than with real reflections, and gives pretty decent results with some fiddling.
The top one slowed down, so I stopped it after 15mins or so, bottom half would have taken much longer than that I gathered.

That's an interesting discovery! I would expect metallic reflection and Fresnel reflection to render in similar times if they are made to be fairly equivalent. Fresnel puts more weight on glancing angles so it's difficult to make the metallic equivalent in that respect, but I wonder if you have the same settings for roughness. With high enough roughness it should be as fast as diffuse. At low roughness (between 0 and 0.2) the render times can vary quite a lot depending on the roughness.

For your "real" reflections are you using a Default Shader there too? How different are your two setups in terms of nodes used and the way they're connected? Can I also ask why you chose to make the metallic reflection blue? I assume your Fresnel reflections were not coloured this way so I wonder why you wanted to do that for the metallic.
Just because milk is white doesn't mean that clouds are made of milk.

Dune

Thanks for chiming in, Matt. I indeed found that with smaller roughness, render time increases. I will set up another test to see what I actually did, and post it.

No, the 'real' reflections are by reflective shader, masked by a reduced PF mask.

I made it blue to have a blue-sky-like reflection, multiplied by a distance shader, so it's bluer (more blue) near horizon. But that was before I added the clouds, so in fact it doesn't make sense anymore.

Dune

I did a new series of tests, but the outcome is now pretty much the same for all versions. I don't know what was the culprit of the slow render in the first few tests (I didn't save those). Perhaps the roughness was very small and masked by tiny fractal, and/or (and I think that's a more logical explanation) the shadows were soft, and the clouds heavier, with more AA (6, instead of 3 in these tests). I might try reconstruct that again...
Anyway, I think it's good to know that for mud a higher roughness is good (0.2-0.4)

Here's the tgd as well, for those of you interested in testing some more... (has some nice stones too)


Dune

No, I haven't tried yet, and maybe I won't if I can get reflections to render faster.

Kadri

I see.
If the free version behaved friendly i would have already tested this.