auto reflection depth prepass

[Neilg]

I would love this. So many times i've gone through a render making sure my reflection depths are all correct, but then there's one object that's seen through an extra layer of glass and it renders a completely different color than the rest of it.

If we could pick a material to calculate the pre pass with (just fully refractive glass, and it's only really refraction that is the issue, reflection is not so bad) and have vray raise the required reflection depths of any objects behind it so they do at least one bounce it would same so much time. It's an arduous enough process trying to work it out as it is and is incredibly easy to miss one.
optimizing reflection depths drastically changes render times - the difference between having everything on 10 and most things on 1-3 is pretty huge so it's a fairly important optimization step for us, but it's so difficult to nail it with the optimum result.

I have no idea how difficult this would be to make but it seems like it would be a fairly logical process. If it was resolution dependent then we could happily render it super low res with no aa and know that any details that it doesn't catch are going to be small enough to not matter.

[joconnell]

Hmm - would it be worth doing some kind of script to give most things that aren't glass a black colour, everything that is glass a normal glass material but set the exit colour to something obnoxious so you could diagnose quickly via a bad quality render?

[Neilg]

It's not the glass' refraction depth that's the issue - it's the reflection depth of the surfaces behind it. exit color would never show up.

setting the refraction depth to 20 on the glass doesnt do anything - i need to get the reflection depth of the walls above a certain amount because it counts travelling through the glass as one.

In this example the glass has 50/50 for reflection and refraction depth. the wall has 4, 3, and 2 as it's depth.
because it travels through double sided glass before it hits it, each surface it hits uses one up and it ends up set to 0 by the time it finally hits it. a reflection depth of 3 becomes the minimum to get anything to show up when it's behind a single pane of glass.
it's a major issue in the way depth tracing works in vray, trying to optimize them to be exactly what you need to get the surfaces to look right basically means you cant render the scene with any glass in.

edit: maybe the request should be for refraction traces to stop using up the reflection traces of objects behind them.