VRayVolumeGrid offset

[Yannick]

Hi,
I have been importing vdb simulation in Maya with the VRayVolumeGrid node, which is really good.
I had to offset a sim by a few frame and I have to say the documentation is not very clear about which parameter to use. I had a few colleagues looking at the definition of the parameters and nobody was clear about what they do.
the main confusion is about the cache start and the play start.
It is quite confusing to offset a sim by a few frame. After a few trial and error, I manage to offset my cache by 6 frame earlier, by putting -6 in the cache start.
From the doc I didn't read the cache start to be like an offset.
In my case, i wanted to start the cache 6 frames earlier, I though I would need to place the new starting frame for my cache in play start by that didn't work.

Could the doc be clarified? Maybe with some examples?

Thanks,
Yannick

[yordan.madzhunkov]

Hi Yannick,
Before I answer you question I will suggest you to update your V-Ray for Maya to most recent nightly build. You will get a working VolumeGrid preview in Maya viewport. This will help you to set the animation parameters to match your desires without having to read our confusing documentation.
The 'cache start' animation parameter is the one you should use. It works in the following way:
'cache frame' = 'cache start' + 'maya frame'

'cache frame' - which frame you want to render/visualize
'maya frame' - which frame is display in maya timeline

As for our confusing documentation, I will try to update it as soon as possible.

[Yannick]

Hi Yannick,
Before I answer you question I will suggest you to update your V-Ray for Maya to most recent nightly build. You will get a working VolumeGrid preview in Maya viewport. This will help you to set the animation parameters to match your desires without having to read our confusing documentation.
The 'cache start' animation parameter is the one you should use. It works in the following way:
'cache frame' = 'cache start' + 'maya frame'

'cache frame' - which frame you want to render/visualize
'maya frame' - which frame is display in maya timeline

As for our confusing documentation, I will try to update it as soon as possible.

Hi Yordan,

thank you for your answer.
i will see if we can update to the latest nightly but I doubt it as we are right in the middle of production.
But is it is good to know that the volumegrid now support the fluid preview.

So from your answer, cache start is simply an offset?
In my case my scene works between frame 1001 and 1050, so in order to get my cached fluid to start 6 frames earlier, I would need to put -6 in the cache start?
If this is the case, why not simply call "cache start", offset, which is quite common in Maya.
The doc mention:
Cache Start - starting frame for the sequence to read. Can be used to skip cached frames at the beginning that should not be used.
It sounds like the option is use to skip frames, how does this work?

Also what is the difference with "play start"? from the doc:
Play Start - position on the timeline (in frames) where the sequence will be placed.
Sounds like an offset as well but where we enter the starting frame, like in my example it would be 995?

Thanks

Yannick

[Svetlin.Nikolov]

Hello Yannick,

We updated the docs - basically Play Start is the frame on the timeline where the cache file with index Cache Start is placed. This way, when you change the play speed, the cache sequence is stretched or contracted around this frame.

[Yannick]

Hello Yannick,

We updated the docs - basically Play Start is the frame on the timeline where the cache file with index Cache Start is placed. This way, when you change the play speed, the cache sequence is stretched or contracted around this frame.

Thanks Svetlin,
it make more sense now, but I would suggest to explicitly say that the play start is a frame offset, this will help non english speaker.

Cheers.