The right way to render with displaced geometry?

V-Ray V-Ray Common Render Theory
1

Hi,

I have a scene setup of a park with a small area of gras using VRayDisplaceMod. I understand that calculation of displaced geometry is not multithreaded but I am not sure in what way that would affect renderingtime. When rendering with VRayDisplaceMod the precalculation drops down to one core for all prepasses and for the hole scene area - should it not just be for the small area of displaced gras?

If that is the way it´s supposed to do, how does people get around it then?

Should I calculate the prepasses without VrayDisplace turn on and then save a irradiance map and then turn it on for final render?

Should I render the hole scene without any displacement, then render only the small area with displacement and then put it together in Photoshop?

I will be grateful for any other suggestions.

Preisler

2

have you tried raising the dynamic memory limit? default is 400 mb, which may not be enough in your case.

3

Yep! I am running 4000 mb - and it dos not seem to have any affect setting it higher.

Preisler

4

Something that affects displacement mod in a massive way is the number of modifiers you have - if it’s lots of small pieces attach them all into one edit poly and just use one modifier.

5

Thanks Cubiclegangster!

I have four small gras areas and therefore four displayment mods - is that a lot?

Do you have any comments on my first question? I believe you have a lot experience with displacement :wink:

Preisler

6

It’s not, but if it’s not going to cause any issues I try to keep all my grass as one.

In all honesty i’m not entirely sure what your problem is - do you mean the IR prepass, or the calculation before the render starts?

Are you using 2d or 3d?

7

Sorry if my question was unclear but it´s the IR Prepass :sweat_smile:

…and 2d with resolution at 1200 and 8 in Precision

Preisler

8

I’m not sure whats going on then, i’ve not seen that before. I usually have all cores working on displacement.

Can you isolate the grass object, see if it’s still doing it and upload it?

9

I will try that.

I was just running a small comparison test.

Rendering size: 5000x2500
Gi: IR+BF
IR map: Min: -5 Max: -2

The scene contains some VrayProxy (8 diff. trees). and some VrayFur for high grass.

IR map with displacement and fur:
1. pass = 01.06.00
2. pass = 03.23.00
3. pass = 11.23.00

IR map without displacement and fur:
1. pass = 00.03.44
2. pass = 00.07.40
3. pass = 00.23.31

I will try with Fur alone for comparison and I will gather some more scene info.

Preisler

10

Well I did some more testing.

First try was the scene with displaced grass but without VrayProxy trees and Fur.
It ran very fast

Secound try was: Scene, fur, displaced grass and no VrayProxy trees.
It ran fast.

Third try was: Scene, displaced grass, VrayProxy trees and no fur.
It ran fast.

With proxy, Fur and grass it runs slowly but with just one of them turned of it runs fast. Hmm - so I looked at rivoli´s post again. Earlier I tried with 4 and 6 GB memory with no change in speed so I thought what the h… I have enough memory and cranked it up to 20 Gb.

And now it rocks!

1. pass = 00.12.58
2. pass = 00.13.06

So thanks to both of you guys for pointing me in the right direction.

Preisler