volumeGrid instability

[mattsmith]

Hi Guys,

We're rendering some FumeFX sims in Vray 3.0, Maya 2014sp3 windows. We're getting good results but encountering lots of instability...

For example a volumeGrid that looked good when rendered locally broke when rendered on the network...the volumeGrid renders as a solid cube. Opening the render file to examine the problem produces the same solid cube and no amount of adjusting opacity values fixes it, but creating a new volumeGrid and copying the settings from the broken grid produces the original, desired look.

Also getting random positional jumps of the grid back to scene 0,0,0.

I've read in another thread that there was a bug related to jitteriness that was fixed in a more recent build. We're using 3.00.01, I'm wondering if we should try a newer version? The instability is really hard to reproduce.

Thanks for any light you can shine my way.

Matt

[ivaylo.ivanov]

There are a lot of fixes and improvements in the nightlies. If they have the same issues, a scene that reproduces the issue will be useful.

[mattsmith]

Hi Ivaylo,

I've isolated the density mapping problem...take a look at the attached jpg. Upper image is a freshly created volumeGrid, lower image is the same grid after saving the file, exiting Maya, relaunching Maya, and reloading the file. The 0 flag of the opacity ramp is being lost.

This might be because I deleted the other flags to create a linear opacity response. Adding a new flag to position 0 fixes the problem. The new flag is kept through saving and reloading. Easy enough to work around now I know what's going on.

The caches snapping back to scene 0,0,0 is something I haven't been able to pinpoint, our sim artist deleted the older sim and replaced it...new version doesn't jump around.

I didn't want to invest time into isolating the problem if this is a known issue with 3.00.01 and could be fixed by grabbing a newer version. Rendering lots and lots of volumeGrids is pretty important for this job we've got so if there have been substantial improvements to the volumeGrid I'd love to hear about them!

-m

[ivaylo.ivanov]

Thanks for the info, will check this ASAP.

[ivaylo.ivanov]

This is not fixed. It looks like an insteresting Maya bug actually. What happens is that your first point is at 0, 0 with linear interpolation. This is actually the default value, and Maya generally doesn't save default values . You may guess what happens when you load the scene - this point was not written to the scene file at all and it's missing... A work-around is not use the 0,0,linear settings. I will fix this in the nightlies, by probably forcing Maya to save even default values. We should do this anyway, since sometimes we change default values in the volumge grid which may cause old scenes to render differently.

[mattsmith]

Good to know, thanks.
A follow-up to this, the Incan Ramp color also has the same behaviour, see attached images

The work-around is to key the first flag at 0,0.


probably unrelated, but maybe worth mentioning is that when i disconnected the vrayTemperature textures from the emRampColor (to see if that was causing any problems) I got this error:

disconnectAttr VRayTemperature2.outColor VRayVolumeGrid3.emRampColor[1].emRampColor_Color;disconnectAttr VRayTemperature1.outColor VRayVolumeGrid3.emRampColor[-1].emRampColor_Color; disconnectAttr VRayTemperature1.outColor VRayVolumeGrid3.emRampColor[-1].emRampColor_Color; disconnectAttr VRayTemperature1.outColor VRayVolumeGrid3.emRampColor[-1].emRampColor_Color;
// Error: line 1: The destination attribute 'VRayTemperature1.outColor' cannot be found. //
disconnectAttr VRayTemperature1.outColor VRayVolumeGrid3.emRampColor[0].emRampColor_Color;disconnectAttr VRayTemperature1.outColor VRayVolumeGrid3.emRampColor[-1].emRampColor_Color; disconnectAttr VRayTemperature1.outColor VRayVolumeGrid3.emRampColor[-1].emRampColor_Color; disconnectAttr VRayTemperature1.outColor VRayVolumeGrid3.emRampColor[-1].emRampColor_Color;
// Error: line 1: The destination attribute 'VRayTemperature1.outColor' cannot be found. //


I'll update this thread if I encounter any more issues...one thing we hit yesterday was the playback settings didn't seem to be hooked up....the cache playback was fixed to whatever it was simmed at, whether we used manual animation control or frame index...

Best Regards,

Matt

[ivaylo.ivanov]

Yes, the 0,0 bug affects all such ramps. This disconnecting error seems like a Maya issues also, happens with any ramp control. Will check this animation control issue.