vray meshlight sloooooooow

[super gnu]

ive got a scvene where i need to use proper raytraced mesh lights ( curved lights, shining on vray fur) so no "store with irradiance map" or vraylightmtls for me..

however that part of the render takes longer than the rest put together - and the rest of the scene (mostly vrayfur) is lit by normal vraylights..


why is the meshlight so slow... ? i remember vlado saying that it has incorporated adaptive sampling, in another thread somewhere where someone was proposing a much faster vray light implementation using distance based adaptive sampling.


any tips to speed things up? cutoff? bias? mesh complexity / area? a load of small rectangular vraylights to approximate the curve?

id do a crapload of testing but im on an extremely tight deadline.

any help appreciated.

[tricky]

Could you occlude a simpler vrayplane light with some geometry to simulate the shape of the light?

[super gnu]

nice idea but unfortunately i cant see how to fit a large rectangular light into my space.... ended up with a string of 200 vraylights set to sphere, renders 11x faster than the mesh...

[vlado]

We are working on improved sampling for the mesh lights, but in V-Ray 2.x there's not much to do except to increase the subdivs of the light a lot.

Best regrds,
Vlado

[super gnu]

so, increasing subdivs might help speed things up..? man i love the dmc sampler. does polycount of source mesh affect rendertime? to be honest im using a simple curved spline, but i didnt check the subdivs, maybe its quite fine tesselation..

[henning]

Have you tried using a vraylight material not in direct light mode but with one pass of brute force GI? It will be slow, but last time I compared this and meshlight the vraylight material won. Although my situation was totally different...

[super gnu]

yes ive found this int he past, single bounce gi on a vraylightmtl is faster than a meshlight.. that suggests to me some serious optimising is needed on the meshlight system!

however in this case that would require me to either render the lights separately or render my whole scene with BF lighting.. which would be a killer. at the moment it renders nice and fast and looks good with imap.

[Neilg]

does polycount of source mesh affect rendertime?

From my experience, yeah - keep it as simple as possible. 6 sided circles with the top 4 deleted and very rough curves are the order the day. Use a vray light mtl with gi turned off if you see the object so you can have a much lower resolution one cast the light.

[AbeMata]

Better yet, you can have your meshlight or lightmtl only affect reflections/spec and have a seperate vrayplane light affect diffuse only. That is if you need the reflection to be a specific shape other than a plane or sphere.