2 Quick Questions. Lava and falling paper.

[mightcouldb1]

I am trying to create two different effects.

My question regarding the lava is:

I want to create a lava waterfall using viscous SPH, but I want to minimize texture swimming when using a procedural shader like the default lava shader. Can someone toss a couple ideas my way for a solution to this?

The question regarding the paper is:

How can I create multiple falling pieces of paper that move realistically instead of using instances? I want them to flow like a piece of paper in the air does, but I want to have about 50-100 of them.

Thanks in advance for any help.

[sam.h]

For the paper thing, I think you should use cloth and get some kind of wind resistance force.

I played around with that a bit, check it out here: http://ihoudini.blogspot.com/2009/05/cloth-and-wind-resistance.html

[mightcouldb1]

Hey Sam, thanks for the reply. I've been following your blog for a while now. I am definitely considering using cloth for the paper effect, but I still not sure how to go about making multiple pieces of paper fall that are all simulating simultaneously.

I was looking at this post: http://forums.odforce.net/index.php?/topic/8929-emit-rbd-objects-from-particles

This person is using the point velocity to create an initial velocity for the rbd objects to use in dops. To be honest, I am having a little bit of trouble breaking johner's scene file down. What do you suggest that I do to create multiple pieces of cloth that I could "emit" from some kind of source geo?

[sam.h]

It kinda depends on what you need, there are a bunch of different ways to approach the problem ...

1. simulate 1 piece of paper at a time.

good for stability, nice and modular etc.

wont interact with each other (maybe you could simulate a few at a time, if the viewer sees two pieces interacting then it would sell the effect)

2. lot of different pieces of paper in one sim.

pieces interact

you would have to resim if layout changes

I would say this would be slowwww.

You would have to start with all of the papers in the sim. Unless it is possible to add new geo to the object during the sim. The docs say that the SOP solver can be used to change topology, which I would assume means that new pieces of cloth could be added. I have tried doing this before and it didn't work. I emailed support about it and apparently it is a bug ... anybody got this to work?

3. lots of different dops cloth objects. - I have never played around with dynamically adding objects to a simulation in DOPs, maybe somebody else can help here?

If I ever get to go home from work I will throw together an example of the 1st option, I have found wedging simulations really useful for a lot of things.

[brianburke]

For falling paper in a student project (

), I ruled out DOPs pretty early on because of the scale of the simulation. Breaking the effect up into two layers, one in POPs and one in SOPs worked pretty ok.

The POP net is a VOP POP doing its best to simulate the effect of gravity on paper in the air. We shot a bunch of reference footage and found that the paper tended to float and then drop quickly, travelling laterally a lot while floating and very little when dropping. All of this behavior was done in a VOP POP, most of it driven by noise. The SOPs setup then analyzed the velocity of the paper and a some flags from the POP net which pointed out what "mode" the paper was in (falling, fluttering, sliding on the ground, in the vortex, etc) and assigned appropriate animation to a grid with a stamping. The animation was created with various deformers.

Regardless of weather you intend to do something like this with POPs and SOPs or not, I would highly recommend trying to break the effect into discrete layers rather than trying to accomplish it in one fell swoop. This will allow you to get the bulk motion and behavior, and add subtlety on top.

[mightcouldb1]

Thanks for the reply Sam and Brian.

Earlier this year I attended a behind the scenes presentation for the movie "Up" and I remember Gary Bruins talking about falling leaves. I believe that he was either using ODE or instances on particles and testing for when the normal vector was parallel or perpendicular to the y axis to speed up or slow down the geo. I'm going to try and figure this with VOPS using a similar method that Sam used to simulate the cloth wind resistance by finding the dot product of the normal vector in relation to the up vector of some geo(I'm assuming this is the way to go, right?). I'll post my progress as it develops. Thanks again guys!