Caustics bug

[Neilg]

This may not actually be a bug - it may have been a bug in 3.6 which I was abusing the functionality of, but it was great functionality and I used it often.


Often for caustics we'll render them as their own pass in direct visualization mode, then we'll project them back into the main scene under the appropriate geometry so that they show up in reflections and refractions.
When working with 10k stills it also allows us to use lower caustic subdivisions and stack renders using AE's wide time - meaning we can queue up 50 frames of an animation then stack into one totally noise free version in the morning. Results in beautifully soft & smooth caustics with very little to no messing around - if it's noisy, stack up more frames.

A key feature of this was that when you checked off 'cast shadows' in the object creating caustics it became invisible. Now in vray next checking off cast shadows also prevents the caustics from being cast. I've tried camera clipping, vray clipping planes, every combination of object and vray properties and as far as i can see, there's no way to make the object causing the caustics to be completely invisible during direct visualisation anymore.

Any chance we can bring this feature back, even if at the time it was an unintended bug? This was the only reliable way we've been able to use caustics in vray for years because doing it 'properly' requires so much tweaking and just isn't worth the time investment.

The expected result is the image attached. I dont think it's possible to achieve the same thing in next. The scene as is renders black in vray next, due to 'cast shadows' being turned off in the object settings.

Here's the max file - https://we.tl/t-C3ROecFtHS

[Neilg]

This was missed at the time, but we're knee deep in a project and again are finding that the only reliable method we had to render caustics has been removed.

Is there some way i should be changing our workflow in order to get caustics to render on black via direct visualization mode, and also have them visible behind glass?

[Neilg]

Here's a max file. sphere creating caustics, sphere has 'visible to camera' checked off, however it's still visible to camera.

https://we.tl/t-qLgNCt0Wog


What is the workflow to render caustics as a separate pass on black, through refractive objects? Is it possible, or has that functionality been completely removed?
Is there a way to switch off 'dont render final image', but have vray not render the lights in the scene and only the caustics pass?

[tanya_to]

Hello! Thank you for the scene. Could you try to disable "Direct visualization" and "Don't render final image" and then exclude plane object in V-Ray Sun's exclude list to see if this will work for you.
Best, Tanya

[Neilg]

Hello! Thank you for the scene. Could you try to disable "Direct visualization" and "Don't render final image" and then exclude plane object in V-Ray Sun's exclude list to see if this will work for you.
Best, Tanya

But i'm trying to use the direct visualization pass - the caustics interpretation in a render is pretty bad, doing a post production noise reduction on a number of direct visualization passes which are stacked is the only way i've figured out how to get good looking caustics. That way it's a fire and forget method which takes minutes to setup and about an hour to render for a clean 6k image.
I realise the previous post was misleading, it was a continuation of the first.

Trying to find the sweet spot in a single pass with the correct number of samples and interpretation settings takes WAY longer than an hour. After 2 hours of work for one shot I now have a 3gb caustics file and it's still not good enough. SO i guess i need to re-calculate the whole thing again?
being able to add frames to a sequence and stack is much easier. if it's noisy after 10, 10-minute frames, queue up another 10. etc. nothing is wasted.


edit: setting max photos to 1 gives me a render of the raw caustics samples, but then they're not visible through glass again - making it no different to using 'dont render final image' & 'direct visualization'. Changing the sun to include or exclude only makes a difference when there's interpretation.