Render viewport subdivision - strangeness.. :P

[caligra]

Hi, I just want to share my experience during the weekend.

I have these huge renders 7000x7000 that I needed to do. And I needed to render the viewport subdivision on my objects.

Everything worked great on the 10% renders (700x700), but as soon as I rendered the full size, vray told me that it would take estimated 40 hours to complete, the light cache...

Imagine my frustration since I had deadline today, and I had 5 images.

Ater tons of tests, I ended up killing the render viewport subdivision, and manually smoothed my objects and I got the images rendered in approx 2h each.

So my point is: Maybe you should either disable the feature completely, or look into it, because it seems to be overworking/overanalyzing/exaggerating its computations by a factor of 1000 or more - atleast at high resolutions.

[vlado]

V-Ray tries to subdivide viewport subdivision down to pixel level; if you have very large renders, this results in many, many, many (did I say many ) triangles. In these cases, there are two things you can do:

1) Increase the "Edge length" parameter for the default displacement settings (you can generally increase it twice every time you increase the resolution twice). In your case, since things were fine at 700x700 with edge length 4 (the default), then for 7000x7000 you can try maybe something like 100.

2) Make sure the "Dynamic memory limit" option in the System settings is large enough. The default is 400 MB but for most scenes this is way too low. Setting it to 0 will remove any limit, but might overflow the physical memory of the machine, which will slow down the rendering a lot.

Best regards,
Vlado

[ivaylo.ivanov]

Hello,
You must use the vray attributes to control the level of subdivision (Attributes->VRay->Subdivision and Displacement Quality on the shape that will be subdivided). If you don't, the default level will be used (which is quite big - 256)

[caligra]

oh, great info.. Thanks alot, but why doesn't vray do this automatically based on the render size?
Is that because theres no real formula for it?

[vlado]

oh, great info.. Thanks alot, but why doesn't vray do this automatically based on the render size?
Is that because theres no real formula for it?

It is somewhat hard to predict what kind of settings would be useful in the end. In any case, I have been thinking of a way to adjust the settings based on the resolution as other people have also stumbled upon this issue

Best regards,
Vlado