Volume Rendering Particles as Liquid Volume

[~nature~]

Hey,everyone,

Nice day here^^

Rendering tons of particles have been such a hot topic in the visual effects industry, To my knowledge, I know the rendering is mainly based off tons of particles simulation whether via layered simulation(like delayed load in houdini or krakatoa in 3ds Max) or via run time particles interpolation based on somewhat low-res particle simulation(e.g. using renderman DSO), like the foam ball and splash effects in the film surf up and sandman in Spiderman.

-As tons of particles finally define the volume so I am wondering if it is possible to render the following splash volume directly via some volume shader(maybe pyro shader) from somewhat small amount of particles simulation ?

-And anyone knows about "modular shading strategy" in the digital water shading in the film Avatar ? I only came across this concept in the abstract of the talk in siggraph 2010.

Any ideas would be appreciate.

Best regards,

[lukeiamyourfather]

I'm not familiar with the "modular shading strategy" but a water spray shader for particles is pretty straightforward in most cases. Use a primitive node and set the particle render type to disk. Then make a Mantra shader builder and use a lighting model node set to isotropic volume. Use deep shadows to light it. The isotropic volume mode tells the lighting model to ignore normals and apply just the shadow. Additional noise and things can be added from there but that'll get the basics going. I would also be curious to know other ways of approaching this, maybe instanced volumes or sprites and other things could work too?

[Macha]

You can use the volume from attribute sop to create volumes from particles. It needs a bit of fiddling to get a smooth pleasant result but it is possible. You don't need that many particles to get a detailed look. I've done that with fire once and I added extra detail by using a ramp in the shader to get thin crispy lines.

It was fast and worked well enough but it isn't quite as straightforward as just particles. There were frames and angles where you could tell it was a low res particle system behind but I could get around it with clever angles and emission.

Edited June 2, 2011 by Macha

[Macha]

Here's a detail of it. I'd guess, uhh, 100 particles did this. The motion was good.

The second image shows what happens when it goes wrong. Not enough particles so the falloff is very fast.

I had to make my own volume shader for this because the default ones didn't work well. I found that very tricky to get right, especially the falloff because it doesn't seem to behave in a linear fashion but in some other, weird way.

Edited June 2, 2011 by Macha

[~nature~]

Luke, Macha thanks for your ideas.

I have tried, but it always resemble the smoke rather than the liquid feeling.

I am wondering what is the key featurse distinguishing between the smoke volume and liquid volume. fast fall off and the light scattering process?

Here is the pics from avatar digital water, it looks really cool, both from the rendering and simulation, and I am curious about the way they approach such volume scattering effects in the shading as what they called in the siggraph 2010 "modular shading strategy".

[lukeiamyourfather]

Luke, Macha thanks for your ideas.

I have tried, but it always resemble the smoke rather than the liquid feeling.

I am wondering what is the key featurse distinguishing between the smoke volume and liquid volume. fast fall off and the light scattering process?

Here is the pics from avatar digital water, it looks really cool, both from the rendering and simulation, and I am curious about the way they approach such volume scattering effects in the shading as what they called in the siggraph 2010 "modular shading strategy".

If there was a paper associated with that then I suggest checking that out. However I assure you the method I shared does work in a lot of situations. Is it what they used in Avatar? No, but who cares if it works.

[jackytop]

Here's a detail of it. I'd guess, uhh, 100 particles did this. The motion was good.

The second image shows what happens when it goes wrong. Not enough particles so the falloff is very fast.

I had to make my own volume shader for this because the default ones didn't work well. I found that very tricky to get right, especially the falloff because it doesn't seem to behave in a linear fashion but in some other, weird way.

That's nice Macha.

Making a volume from the point is very interesting. Would you give us a simple hip file that tells the process ?

[bhaveshpandey]

You can create a volume container using a volume sop and use volumefromattrib sop to fill in density data using a particular attribute from particles or any point cloud.

check the help docs for these sops they have examples for these.

hope this helps.