VDB displacement MtoA doesn't work

[40082922]

So, first I wanted to thank Lee Griggs for all of his amazing work and inspiration that he's bought me and I'm sure a lot of other artists.

Now, on to the issue. The issue that I've been having has been with trying to displace an Arnold volume within Maya. I am unsure whether this issue is because I'm using a vbd file for the Arnold volume or whether that is ok and the issue is with the volume itself. The vbd file I'm using came from openvdb.org and I'm using the explosion vdb. Strangely, it seems as though the displacement works perfectly fine with standard shapes, very similar to the simplified scene given to us by Lee Griggs within his polymesh to volume tutorial. It seems that any displacement does not affect the volume at all whether that be using a camera projection or whether that be using a simple AINoise node. I'm wondering if there's something that you have to do that is different with an Arnold volume than there is to do with a mesh being used as a volume; if so would be lovely to have some feedback.

Thank you in advance!

[40082922]

@Lee Griggs

I've seen you've been incredibly responsive all over the forum and would love it if you could lend a hand here. I was trying to follow the Polymesh to Volume tutorial you posted when I ran into this problem.

ps. im happy to post any and all files as well as screenshots if needed.

pss. sorry for the "@" to get attention.

[lee_griggs]

Thanks Benjamin. I just tried the bunny scene from this tutorial and it works fine.

[40082922]

Thank you for your reply! So after some fiddling around with values and looking at the tutorial you linked, I've worked out it was actually working the whole time just with unnoticeable displacement as it was all too small. But this actually raises another issue. I'm using a camera projection to drive the displacement of the volume but I need to set the output max of a range to a crazy-high value like 80-100 before I can see a difference. This means that applying the same texture to both the Arnold volume and the polymesh I am rendering as a volume results in the mesh being invisible/flying way out of sight. I feel like there must be an issue here as you said about using a value of 8 where I am having to use 80 for similar results. Any thoughts on what's happening?

[lee_griggs]

What bounds padding value are you using? Can you share a simple scene?

[40082922]

I'm so sorry for the long reply, I didn't get a notification. I've got a scene here that demonstrates my problem quite well. I have an image going through two range nodes into identical standard volume shaders and have one assigned to the Arnold volume, using a VBD and I have the other assigned to a Sphere I am rendering as a Volume. Both have volume padding of 0.05 but you'll see that one requires over 10 times the amount of output max value from the Range node to get a similar amount of displacement. I'm stumped and I'm sure I'm doing something wrong here.

I dont know what you mean by bounds padding. Can you point me in the right direction?

scene-for-lee.zip

[lee_griggs · Accepted solution]

Sorry, I meant to say Volume Padding (which looks fine in your scene). I would make sure step_size and volume padding are the same for both the sphere and the volume.

There was no texture or .vdb in the zip file. I rendered it and saw a difference between the volume and a mesh. If you increase the Density in the Standard Volume it should be less noticeable.

I did notice that your Diffuse, Specular and Transmission samples were unnecessarily high for this scene. Lowering these should speed up your renders.

[40082922]

All awesome advice! Thank you! I have no idea why the .vbd wasn't in there, I must have to zip all of the files used in the scene as well I assume. I still don't understand where I went wrong in following your tutorial though. I can't seem to get the displacement right at all. Your artwork seems almost like liquid worlds and I guess a lot of that effect comes with playing with every setting and getting it all perfect. It just seemed so straight forward in the tutorial (Polymesh to Volume) but things like the camera projection and the final node structure are hiding a lot under the hood.

I know this is a lot to ask but I would love to see a version of this screenshot (below) but with the menus opened up so that I might be able to see the node graph in a little more detail? It's a lot to ask and it's absolutely fine if not.

[lee_griggs]

There is no hidden sauce in that screenshot. I think its more to do with the volume that you are using. Have you tried a different one?

[40082922]

Well, some of the other .vbd files from Openvbd, but all of them have similar effects. Generating my own is a little beyond me as my specialism is usually sculpture and solid texturing. I think I am getting some better results now though, from playing around more with the rendering and the subtlety of the effects. I see your texture fits the purpose really well so maybe ill find a new one thats a little less dense and use some form of gradient to mask out the parts of the mesh I want to retain shape. It'll probably just be a lot of experimentation from here on out to get some new results. I expect some colour and some better lighting will help a lot too. Before I mark this as answered, just really quick, you see how you used a texture projected through the camera? There is a render cam shape that goes into it and another node. What is this and where does it plug in? You don't mention this in the tutorial.

Anyway, thanks so much for the help, Lee. It's really nice of you to take the time.

[lee_griggs]

Yes, it does take a lot of fiddling to get something that works, unfortunately. Maya creates those nodes when you choose to project a texture. Choose perspective in the projection node and then choose your camera underneath. Good luck!