Speed GI vs. No GI in general

[TubeSmokeGuy]

Hi!

I noticed that VRay added this adaptive lighting stuff, like adaptive lights and adaptive dome light for speeding up rendering. But that all needs active GI to get a light cache calculated. Am I right so far?

So I wonder if rendering with GI and all the fast render advantages which are unlocked by light cache, is now faster than just use direct lights? Is it possible to make a general statement to this?

So thanks in advance!

[^Lele^]

The answer to the first question is a yes, it's true for the time being.
Further, currently one needs a LC to be calculated.

The answer to the second, very interesting question, is more nuanced, and as such not quite answerable exactly.
A case could be made in specific scenarios (f.e. many hundred, or thousands of lights) where an adaptive lights approach would shave off heaps of time, time the primary BF GI wouldn't likely eat all up.
Further, one could make the GI somewhat more limited than at default (the LC has 100 bounces...), in turn shaving some primary BF GI rendertime by virtue of a shorter retracing phase (it's of course easier to calculate 3 GI bounces than it is to calculate 100, especially with BF algorithms.).

For most scenes, however, things could swing a bit this and that way, so no general statement can be made.
You're surely welcome to try it out though! :P

[vlado]

I will have to make some tests for exact render times; in general though we continue to improve the "no GI" scenario as well. For example in Update 2 of V-Ray for 3ds Max, we have more efficient handling of direct lights for the case when the light cache is not available or when GI is disabled.

Best regards,
Vlado

[TubeSmokeGuy]

Hey this sounds very interesting to me. I look forward to check this out after release!

The disadvantage of when i want to get a light cache for speedup lighting is the fact, that I need the expensive primary engine brute force, which takes long to calculate or irradiance map, which takes some extra work when i want to get it splodge-free in animations. Light cache as primary engine is not usable cause of the strange look in the final image (i don't know why it is pickable at all). So i think its not really worth it to use the GI just for getting a light cache to speed up the direct light calculation by all the adaptive stuff the light cache provides?

[piotrus3333]

what about setting lightcache for primary and secondary bounces (or less - do not know what kind of quality lightcache needs to be helpful for adaptive dome etc) but limiting GI contribution to 0 ?

[TubeSmokeGuy]

Do you mean with "GI contribution" the GI multipliers for primary and secondary engines?

But at all what you suggest is some kind of work arround. Yes I know - making 3D is allways a chain of workarrounds but I noticed in the early past that it all becomes a little bit cleaned up, more structured and easier to use. I think thats a good way.
So what I would prefer in this case is something like a checkbox in the render setup, where you can directly activate something like "enable lightcache support for direct lights", which calculates a lightcache as a prepass which has no visible effect in final image, just to boost the adaptive light calculation at all for no GI scenarios.

[piotrus3333]

Do you mean with "GI contribution" the GI multipliers for primary and secondary engines?

yes.
(10 characters per post limit thank you)

[^Lele^]

what about setting lightcache for primary and secondary bounces (or less - do not know what kind of quality lightcache needs to be helpful for adaptive dome etc) but limiting GI contribution to 0 ?

It'd be better to set bounces to 1, i'd wager (but haven't tried it!).

[piotrus3333]

what kind of speed gains and scenes are we talking about here? over the years every now and than I was trying no-GI (architecture) and it was simply never worth it. one exception was foliage - I was replacing GI with green VRayAmbientLight. but last time I used it was like 4 years ago probably.

[TubeSmokeGuy]

It'd be better to set bounces to 1, i'd wager (but haven't tried it!).

Sorry, which parameter do you mean exactly?

piotrus3333 ist a discussion abaout a general case - because of the new adaptive boost features for calculation of direct light in combination with lightcache.

[piotrus3333]

there is no such thing as general case GI wise. you either need it ( than there is still/animation issue to consider) or you don’t.
I always considered VRay to be designed to be used with GI. MIS option for VRayLights for example.

[^Lele^]

what kind of speed gains and scenes are we talking about here? over the years every now and than I was trying no-GI (architecture) and it was simply never worth it. one exception was foliage - I was replacing GI with green VRayAmbientLight. but last time I used it was like 4 years ago probably.

Difficult to assess.
We should test again once SP2 is out and the new tech is available.
For many lights, it's seriously substantial (in the order of how many times quicker it is, rather than percentage shavings) in the current state, bound to perhaps become smaller with the new tech in SP2 which doesn't need to rely on the LC.

TubeSmokeGuy the lightcache number of bounces under the expert mode LC rollout

[piotrus3333]

Difficult to assess.
We should test again once SP2 is out and the new tech is available.
For many lights, it's seriously substantial (in the order of how many times quicker it is, rather than percentage shavings) in the current state, bound to perhaps become smaller with the new tech in SP2 which doesn't need to rely on the LC.

I was rather referring to OP's expected speed gains.
many adaptive lights - do not need numbers here hehe - its enough to see it once in action.