Long pre render times

What does vray do exactly from the time that I hit 'render' to the moment where the frame buffer and status window show activity ?

I have a scene in Rhino where, regardless of what vray settings I use (low or high quality), it always takes a long time to start the pre-passes. I tried turning off-the-camera objects but it doesn't seem to make any difference. I also happens with GI off.

However, when exporting only the objects seen by camera and rendering them as separate scene the process starts way faster.

This suggests to me that vray still considers the objects not seen' by the camera by turning off layers or by hiding the objects individually.

Thoughts ?

EDIT: I tried leaving ONLY one object vs. ALL objets (some 1,200 objects, file size is 30mb) and takes exactly the same time, about 4 minutes to see any activity. Also the framebuffer time stamp doesn't take this wait time into account ...

And by the way all vray windows become frozen so I cannot cancel. Is this normal ?

You may want to ask directly in Chaos group if you want an detailed answer. As far as I know, when you click render, the software has to compile or collect all geometry and textures, send it to their render engine and start calculations of Gi and what not. This means that if your textures are large or your geometry is large in number (triangles) it will take more time to collect. Here is when VRay check how much RAM you have also, so if it can't fit everything in RAM it start to divide your scene in priorities and the rest is loaded only when it is visible to the camera. This mean also reflections, shadows and GI; for example if you have elements outside of your camera but they are projecting shadows over the camera view, or they maybe visibles in reflections they are included too.

Remember that glossy materials also count reflections, if you are doing a soft glossy grass in your scene that grass also may include object outside of the camera view.

I am not sure how optimised is VRay for Rhino but each version of VRay has different performance, obviously because the different architecture of each software. but once everything is within V Ray code, performance should be pretty close.

Francisco,

Everything that you say is true and I'm well aware of that. RAM is not an issue, I have 32GB and looking at the task manager I still have 65% of RAM free. The model is relatively large but nothing out of the ordinary.

You are absolutely right that objects off camera still might cast shadows or contribute to reflections. The reason that I was posting this is because, as I explained earlier, even leaving only one small object and freezing/hiding layers for the rest, still gives me exactly the same delay. That's why my first question was whether vray ignores the fact that the layers or objects are off and it calculates all the geometry anyways which doen't make sense and I refused to believe unless there was something that I was missing...

Well, guess what ? I did some tests today and If I deleted everything in the scene and leave that single object as opposed to hiding or turning off layers and there is no delay, like I would expect. So I have to conclude that either Rhino or Vray don't care if you freeze layers or hide objects and still considers ALL THE GEOMETRY in the pre-rendering stage regardless of being visible or not. Why on earth would vray need to collect geometry that is turned off and for all purposes it doesn't exist !

I look forward to a logical explanation ...

Thanks for your input anyway

I am not a Rhino user, so it would be very interesting to get an answer for that for sure.

In Rhino you can 'hide' objects or turn off layers, or a combination of both. After doing more testing I should correct my previous posts by saying that the problem seems to be only when hiding objects where Vray still considered them as geometry in the scene, whereas turning off layers actually does the expected effect by vray not considering them as geometry.

I'm inclined to believe that it is a problem with the way that vray treats hidden objects. I've tried with a another two render engines and they respond properly to hidden objects with shorter wait time like one would expect.