Time interpolated irradiance maps.

[cg_Butler]

Hi all.

 

Bit of a debate about something that i wondered if any of you can answer.

 

When having moving cameras and objects we are obviously using Animation Prepass and Rendering modes. The debate comes after the following statement.

 

"Light cache:

 

You now have two options depending on your workflow, if you have rendered your animation with use light cache for glossy rays ticked, you will need to leave your light cache as the secondary GI engine.

 

Keep it in single frame mode and have use camera path ticked.

 

If you have rendered without use light cache for glossy rays, disable the secondary GI engine leaving only the irradiance map as the primary GI engine.

 

You can do this because the secondary GI data has been stored in the primary GI engine via the irradiance map prepass."

 

What is the need for having the Secondary pass as Light Cache when you have "Use Light Cache for Glossy Rays" ticked for the prepass? and no secondary pass if you have it unticked?

 

We are a bit unclear as to why exactly this is the suggested way of doing it.

[salvador]

I don't have expert words here, but AFAIU, and please someone correct me if I'm wrong, glossy rays are calculated at render time using the info stored separately in the LC; if you don't have it because you disabled it, VRay won't look inside the IRRMap for this info and glossies won't render as they should. It's like looking inside two different places A and B. If contents of B are on A and not on B the software will consider B is empty.

 

Pretty lame explanation, I know. . .

 

Look at this: http://www.workshop.mintviz.com/category/tutorials/rendering/

 

these are professional free tutorials that will explain correctly your question

[cg_Butler]

Thanks for the response but I'm still none the wiser......sorry. What you said is what I understand but no one really explains the reasoning.

 

I actually cut my quote from that websites guide on how to set it up!

 

LC=Light Cache

IR=Irradiance Map

 

If the glossy rays are stored at render time, then presumably that is with "use LC for glossy rays" un ticked. Therefore having no secondary bounces makes sense because the LC is saved in the IR map and the render sorts out the glossy refs.

 

So if you do have it ticked, that means that it's storing glossy rays in the LC, so you should have LC in the secondary bounces, to get them from the LC?? But you haven't saved any LC files in the first pass so where is it getting them from? It's so confusing...................

Edited November 19, 2012 by cg_Butler

[jamescutler]

When computing the the prepass the irradiance map does not store light cache glossy information. I am sure there is a reason for this but I don't know off hand.

 

If you have glossy rays ticked you must use light cache in single frame mode for both the prepass and rendering. I believe you can pre-render the light cache using from file with light cache glossy rays on. Then run the prepass and store all the data in the irradiance map allowing you to turn off light cache but it seems a bit long winded to me and you wouldn't benefit from it.

 

You either have glossy rays on and leave light cache as single frame for both the prepass and the rendering. Or leave glossy rays off and render the light cache into the irradiance map during the prepass allowing you to turn off the light cache for the rendering.

Edited November 19, 2012 by jamescutler

[cg_Butler]

Thanks James.

 

Very useful site you have by the way. :-)

 

Have you noticed any difference in the final renders using either way suggested, or even mixing them up? We have triad a few possibilities and all ways seem to give a barely noticeable differences in the final results and render times.

 

We've had use light cache for glossy rays ticked and un-ticked and LC as our secondary bounces on and off (giving four rendering options) and everything pretty much looks the same and render times are no different.

 

I think I'm still confused though about the whole LC being baked in to the IR map. Are the glossy reflections baked in to the IR map as well as the LC when you have use LC for glossy rays un ticked? And if you have it ticked you need to use LC as your secondary pass purely for the glossy rays?

 

Doesn't the LC calculation get baked in to the IR map when you have it un ticked as well? Meaning that because you've got LC on for your rendering pass, you are effectively re-rendering the LC again?

[jamescutler]

If you use light cache for glossy rays, you may notice small artifacts in reflections which can be avoided. Although written for Cinema 4D, the same works for 3ds Max here: http://vrayc4d.com/manuals/faq/how-avoid-artefacts-use-light-cache-glossy-rays. It is known to reduce render times by quite a bit but it would depend on your scene.

 

Light cache does get baked into the irradiance map but if use light cache for glossy rays is ticked, everything but this setting gets baked which means you have to run the light cache the second time. You are rendering the light cache twice but in practice you are saving a lot of rendering time by using light cache for glossy rays, unless of course for your scene you don't experience any gain, which is unusual. you have to have a good amount of glossy materials in your scene obviously for it to be effective.

Edited November 21, 2012 by jamescutler

[cg_Butler]

Thanks for clearing that up. It would explain a lot that i have no gain as i am just rendering people and they obviously have no glossy reflections!

 

We did do another project using it which had minimal reflections so again, perhaps that's why we didn't notice any render time differences of visual difference in the rendered frames.

[jamescutler]

You are welcome, good luck with the project.