Problem with light cache & Transparent Materials

[Sando]

Hi all,

I have an interior scene about 175mb file. I am rendering large scenes of up to 7000x3525 using Irradiance Map and Light Cache. Up until now I've been able to render such large images by using tricks like VRimage and pre calcuation at a lower res. I have been able to find most answers to my questions on these forums but this time I am stuck and can't figure out a way to get around this problem.

First up, I'm running two machines. both are 64 bit, 8gb ram, with quad cores so there shouldn't be much of aproblem there.

I have however narrowed it down to one problem. Transparent curtains. If I have the curtains switched off then the scene will render fine using light cache. If I have them on then light cache process seems to take forever to point where I have left it running over night using two machines and still no progression the next morning.

I have tried using DMC as my secondary engine instead of Light Cache and it does seem to work but to my understanding, light cache gives a better result and is supposed to be faster. Does anyone have any ideas on this?

The other reason for the long render times might be the material. It's basically a diffuse bitmap image with transparency.

Cheers in advance for any comments that might help.

[dalomar_cg]

Re: Problem with light cache & Transparent Materials

First off, running LC with DR is actually not using both machines. Its basically calculating the same thing on both. Just so you know...

Back to the issue at hand. When you have a material that is some degree transparent (ie not fully transparent) then V-Ray will have to calculate two paths...one as if the material was there, and one as if the material wasn't there...and then merge the two based on the degree of transparency. For one transparent object, this usually isn't too bad, but if you have curtains that fold back in on each other, each time a path hits another transparent material it will cause the paths to be "split" again.

I'm not sure if there's something within the LC calcs that causes this affect to be intensified in terms of slowdown. DMC is a brute force calc so it tends to be as "no frills" as you can get, so if thats going fine I would say its not something too crazy.

At the moment my best suggestion would be to try a different material, specifically a V-Ray 2 Sided material and see if that helps get things back up to speed. I think that the 2 sided material will work a little better that a simple transparent material for using in a LC calc within the context of what you're working with.

BTW a quick image of the scene with the curtains would be helpful. HTH

[Sando]

Re: Problem with light cache & Transparent Materials

Hi Damien,

Thanks for the quick reply and correction on a few techincal details. I have attached a small image of my scene. On the right you can see 2 curatins. The one that is furthest into the room has a transparency of RGB 5,5,5. The curtain outside of that has a tranparency of RGB 105,105,105. As you can see this render has seemed to work fine having just the one set. There is supposed to be another 4 sets. Maybe there is just an overload in the scene.

Is there a way to incrementally add the calculations to the light cache similar to the way Irradiance map works?

ps. I have tried to upload an image of 33kb a few times now and it keeps coming up with an error 'upload folder is full'. Is there something I'm not doing right?

[dalomar_cg]

Re: Problem with light cache & Transparent Materials

We are no longer supporting attaching images directly through the forum. If you go to a hosting service such as imageshack.us photobucket.com or flicker, then you can host it there and show it here. I know imageshack will generate the necessary code for posting and its free

[Sando]

Re: Problem with light cache & Transparent Materials

Oh I see. Thanks Damien. I will attempt to do that during the day when I get up at some point.

I think I have sorted out my problem. Firstly I doubled checked the manual and reread your post and found that I did infact have 'doubled sided' checked in the material editer when in fact it should be unchecked which made a big difference. Also having too many translucent materials in the one scene that overlap increase render time too.

Thanks again Damien.